SB2

The discovery of trans-Neptunian objects (TNOs) marked an important milestone in the understanding of the outer Solar System. Due to their environmental conditions, these objects could preserve the most pristine materials that were present on the protoplanetary disk. Studies focused on understanding TNOs physical and dynamical properties can be used to probe planetary formation processes and the subsequent solar system dynamical evolution that followed the formation era.

Nowadays, above 3,000 TNOs have been detected, including four large ones that receive the official designation of dwarf-planets. Analysis of TNOs revealed a compositionally and dynamically diverse population. However, despite all the progress in the last decades, much is still unknown about the composition of the TNOs.

The recently launched James Webb Space Telescope (launched on December 25, 2021) will provide a powerful tool to investigate the TNOs surface composition, where all prior instrumentation has fallen short. The NIRSpec instrument onboard JWST will provide high-quality data that will surpass the quality of the data available by orders of magnitude. DiSCo-TNOs, lead by the Florida Space Institute, is the only large program approved by JWST for the study of the Solar System. With it, we aim to assess the relative ratio of water ice, complex organics, silicates, and volatiles on the surface of a large sample of TNOs. This information is vital to improving models of the formation of our Solar System and other planetary systems. In this talk we present the scope of the DiSCo program, and the tools that are being developed to extract the maximal information from the data. We pay special attention to the compositional modeling technique that uses an implementation of a nested sampling algorithm for Bayesian inference of the abundances and grain sizes distribution of the materials present on TNOs surfaces.

How to cite: De Pra, M., Pinilla-Alonso, N., Souza Feliciano, A. C., Schambeau, C., Harvison, B., Emery, J., Cruikshank, D., Pendleton, Y., Holler, B., Stansberry, J., Lorenzi, V., Muller, T., Guilbert-Lepoutre, A., Peixinho, N., Bannister, M., and Brunetto, R.: Discovering the Surface Composition of TNOs (DiSCo-TNOs) with the James Webb Space Telescope, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1196, https://doi.org/10.5194/epsc2022-1196, 2022.

The stellar occultation technique is a very powerful tool to obtain the size and shape of Solar System bodies with high accuracy [6]. Size determination allows to obtain geometric albedos and, in the case of binary/multiple objects, even the mass density can be derived [3]. Satellites, atmospheres, and rings can also be detected and characterized [1,2,3]. The observation of stellar occultations produced by Kuiper Belt Objects (KBOs) and Centaurs with the James Webb Space Telescope (JWST) offers a unique possibility to extend our knowledge of these bodies [4] by providing key information on the body's ability to retain volatiles, surface thermal properties, roughness, porosity, etc.

We will present our Target of Opportunity (ToO) program [5] accepted within Heidi Hammel's JWST Guaranteed Time Observations (GTO), dedicated to observing stellar occultations by trans-Neptunian objects (TNO) and distant dwarf planets or particularly interesting centaurs (such as the ringed centaurs Chariklo [1] or Chiron [2]). Predictions of such events visible from JWST are challenging due to the chaotic motion of the space telescope around the Lagrange 2 (L2) point. Statistically, we expect there to be approximately a 50% chance of such an occultation of a star brighter than K=19 by a numbered TNO observable from JWST in Cycle 1. We will discuss the possible candidates for Cycle 1 occultations that we have identified so far. As JWST station-keeping maneuvers are executed, the list of possible occultations and their uncertainties will be revised. Very accurate relative astrometry will be performed using the latest releases of the Gaia catalog for particularly promising occultation events through established ground-based programs. Suppose a stellar occultation event is confirmed through such an astrometric revision to have a predicted impact parameter less than 3 times the estimated target radius and to have a 1 sigma uncertainty in prediction less than 2 times the target radius. In that case, the ToO observation will be triggered. JWST station-keeping and trajectory-prediction operations have been studied in the context of stellar occultations by solar system bodies [4]. The accuracy of the trajectory predictions is adequate to support this triggering mechanism up to roughly 30 days before an occultation event: the ToO response time is set to 14 days, the minimum value for a non-disruptive ToO.

The observations will be made with NIRCam and the F070W and F277W filters. These filters were chosen to maximize the flux from the star while minimizing the reflected flux from the TNO or Centaur. This filter combination could change based on the properties of the occulted star and the occulting TNO/Centaur. Other technical aspects and updates on this project will be provided during the presentation.

Acknowledgments. We acknowledge financial support from the Spanish grant AYA-RTI2018-098657-J-I00 “LEO-SBNAF” (MCIU/AEI/FEDER, UE) and from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). Funding from Spanish projects PID2020-112789GB-I00 from AEI and Proyecto de Excelencia de la Junta de Andalucía PY20-01309 is also acknowledged. Part of this work has received funding from the European Research Council under the European Community’s H2020 (2014-2020/ERC Grant Agreement no. 669416 “LUCKY STAR”). M.V-L. acknowledges funding from Spanish project AYA2017-89637-R (FEDER/MICINN).

References

[1] Braga-Ribas et al., Nature 508, 72 (2014)

[2] Ortiz et al., A&A 576, id.A18 (2015)

[3] Ortiz, Santos-Sanz et al., Nature 550, 219 (2017)

[4] Santos-Sanz et al., PASP 128, 959 (2016)

[5] Santos-Sanz, JWST Proposal. Cycle 1, ID. #1271

[6] Sicardy et al., Nature 439, 52 (2006)

How to cite: Santos-Sanz, P., Pinilla-Alonso, N., Stansberry, J., Holler, B. J., Gomes Junior, A. R., Morgado, B. E., Ortiz, J. L., Sicardy, B., Morales, N., Vara-Lubiano, M., Fernández-Valenzuela, E., Desmars, J., Kretlow, M., Souami, D., Braga-Ribas, F., Camargo, J., Benedetti-Rossi, G., Rommel, F. L., Duffard, R., and Assafin, M.: Unveiling the Kuiper belt from the JWST through stellar occultations, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-362, https://doi.org/10.5194/epsc2022-362, 2022.

Earlier reviews of trans-Neptunian light curves reported mean rotation periods of P = 7-8 h (Duffard et al., 2009), and it was also found that the binary trans-Neptunian population rotates slower (Thirouin & Sheppard, 2014), and objects in the cold classical population have larger variability and rotate slower than the non-cold classical TNOs (Benecchi et al., 2013,Thirouin & Sheppard, 2019). While ground-based observations have obvious limitations in detecting long-period light curves the K2 mission of the Kepler Space Telescope allowed long (up to ~80 days), uninterrupted observations of many Solar system objects, including main belt asteroids, Hildas, Jovian trojans, and also the irregular satellites of giant planets. Light curves were also published for a few, selected trans-Neptunian objects based on K2 observations (see Kiss et al., 2020, for a summary). A common outcome of the studies of larger samples, across all dynamical classes, was the identification of an increased number of targets with long rotation periods compared to previous ground-based studies. A similar trend is observed among the data of nearly 10 000 main belt asteroids obtained by the TESS Space Telescope (Pál et al., 2020), and asteroids with long rotation periods were identified in other surveys like the Asteroid Terrestrial-impact Last Alert System (ATLAS), the Zwicky Transient Facility (Erasmus et al., 2021) and the All-Sky Automated Survey for Supernovae (Hanus et al., 2021). 

We have collected the K2 trans-Neptunian object observations between Campaigns C03 (November 2014 -- February 2015) to C19 (August -- September, 2018), which includes 67 targets. Due to the faintness of our targets the detectability rate of a light curve period is ~57 %, notably lower than in the case of other small body populations, like Hildas or Jovian trojans. We managed to obtain light curve periods with an acceptable confidence for 36 targets; the majority of these cases are new identifications. We were able to give light curve amplitude upper limits for the other 31 targets. Several of the newly detected light curve periods are longer than ~24 h, in many cases close to ~100 h, i.e., slow rotators.

There is a very significant difference between the rotation rates of the LCDB and K2 TNO samples (Figs. 1 and 2). The mean LCD spin frequency is 2.71 c/d (8.8 h), while it is 0.87 c/d (27.6 h) in the K2 sample which is more similar to the K2 Hilda and Jovian Trojan spin frequency distrbutions. Thirouin & Sheppard (2019) obtained 9.48±1.53 h and  8.45±0.58 h mean rotation periods for the cold classical and the non-cold classical TNOs. Our mean values for the same dynamical groups (but using different targets) are notably longer: 1.21^+1.58_-0.63 c/d (19.83 h) and 0.83^+1.81_-0.23 c/d (P=28.91 h), respectively. The K2 mean frequency is higher than that of the K2 Jovian Trojans and Hildas, but we could not detect the very long period targets that were observed in these other K2 samples.  

Figure 1: frequency distribution of asteroids. The cyan, magenta, green and blue colours represent the TNOs in the LCDB and Jovian trojans, Hildas and TNOs from K2, respectively.

Figure 2: Frequency as a function of absolute magnitude. Big circles with error bars mark the median values standard deviations for the different samples. The horizontal dashed lines mark the spin frequencies of fast, slow, and very slow rotators (Pravec et al., 2002).  

While there are only three objects with D>500 km in our sample, there are a number of objects -- both with and without detected light curve periods -- that fall in the 300≤D≤500 km transitional zone where asphericity -- hence light curve amplitude -- is expected to drop assuming a single rotating body, assuming main belt composition. Main belt asteroids are already almost extinct in this size range, and so are Centaurs -- for these bodies irregular shapes are expected in most cases. 

While the general trend is that larger objects have smaller light curve amplitudes among TNOs -- a trend followed both by our sample and the LCDB TNOs -- there are a considerable number of TNOs with high asphericity in the 300≤D≤500 km size range. This contradiction could be resolved if TNOs had higher-than-expected compressive strength and become spherical for sizes larger than their main belt counterparts, and remain 'irregular' in the 300≤D≤500 km range. However, their general low density and high porosity point against this scenario. A notable fraction of contact or semi-contact binary systems in which the members themselves are in hydrostatical equlibrium could produce a population of high-amplitude light curves in this size range (Lacerda et al., 2006, 2014). As some authors pointed out, contact binaries may be very frequent, especially in the plutino population (Thirouin & Sheppard, 2018,2019). The long term stability of such systems against their tidal evolution, however, should be investigated to answer the reliability of this assumption. Finally, spherical (rotationally flattened) bodies with large albedo variegations could also explain the observed amplitudes. While the general expectation in most TNO light curve studies was a double peak light curve, in our sample most light curves were found to be single-peak, after comparing the single-peak and double-peak solutions.

Fgiure 3: Light curve amplitude versus the estimated size of the targets in our sample. The region between the vertical dashed lines mark the irregular-to-spherical transition size range in the main belt. Blue and red symbols mark the K2 targets and K2 upper limits, small grey symbols correspond to main belt asteroids. Large gray symbols represent the theoretical maximum light curve amplitudes the of large main belt objects if it was solely caused by the elongated shape of a body with homogeneous albedo.

How to cite: Kecskeméthy, V., Kiss, C., Szakáts, R., Pál, A., Szabó, G. M., Molnár, L., Sárneczky, K., Vinkó, J., Szabó, R., Marton, G., Farkas-Takács, A., Kalup, C., and Kiss, L. L.: Rotational properties of Kuiper belt objects as seen by the K2 mission, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-677, https://doi.org/10.5194/epsc2022-677, 2022.

Beyond the orbit of Neptune lies a sea of small icy bodies known as the Kuiper belt. The surfaces of these Kuiper Belt Objects (KBOs) have remained relatively unprocessed since their formation as a consequence of their distance from the Sun. This means that we can investigate their formation conditions in the early Solar System by studying their surfaces today. Generally, the small and most numerous KBOs are quite dim (r mag > 22), and so it is difficult to study their surfaces spectroscopically. Instead, we can use broadband photometry to take effectively very low-resolution spectra of their surfaces.

When studied spectroscopically, the surfaces of smaller KBOs have generally shown very flat and featureless spectra within certain wavelength ranges. This means that broadband photometry (within those wavelength ranges) can reveal enough information to characterise the optical and near-infrared spectral slopes of these planetesimals. The Colours of the Outer Solar System Origins Survey (Col-OSSOS) has obtained optical and near-infrared broadband photometry of a sample of 92 KBOs, at unprecedented precision (~ ±0.03 mag in optical wavelengths). These broadband surface colours allow small, dynamically excited KBOs to be characterised into a bimodal colour distribution (as with previous colour surveys), along with the identification of potentially outlying surface colours.

As a side effect of Col-OSSOS’s observing technique we have a sample of objects with repeated optical colours, and some repeated near-infrared colours. We also have taken additional optical photometry of a small sample of KBOs with outlying surface colours. This allows us to investigate the possibility of photometric variation across multiple epochs for this sample of objects. Col-OSSOS observed sequential broadband filters on timescales less than the typical periods of small KBOs. Therefore, we can simultaneously fit a linear lightcurve and photometric colours to our photometry and potentially rule out lightcurve effects causing photometric variations. This means that differing colours across multiple epochs implies either differing surface composition, or that our approximation of linear brightness variability across the observing sequence is invalidated. We will present this sample and discuss implications for the spectrovariable population within the Kuiper belt.

How to cite: Buchanan, L., Schwamb, M., Fraser, W., Bannister, M., Marsset, M., Pike, R., Kavelaars, J., Benecchi, S., Lehner, M., Wang, S.-Y., Peixinho, N., Volk, K., Alexandersen, M., Chen, Y.-T., Gladman, B., Gwyn, S., and Petit, J.-M.: Exploring Variability within the Col-OSSOS Sample, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-936, https://doi.org/10.5194/epsc2022-936, 2022.

We report a multi-opposition discovery of 17 Trans-Neptunian Objects (TNOs) with the Chilean node of the Korea Microlensing Telescope Network (KMTNet-CTIO) which has a 1.6 m wide-field optical telescope covering 2x2 square degree field of view. The first survey observations were made with 4 fields around (RA,DEC = 197.6°, -7.9°) every other day from April 5 to April 15, 2019, and recovery observations were carried out every year since then. More than half of the 17 objects were not initially observed in 2019 but were discovered in later years. The observed R magnitudes of discovered TNOs are from ~22 to ~24 and their H magnitudes are estimated to be from 6.6 to 8.5. Of the 17 TNOs, two objects, 2021 GU122 and 2022 GV6, have been found to be detached objects with perihelion distance greater than 40 AU. 2022 GV6 has an estimated semi-major axis of 110 AU and is currently passing near its perihelion. Most objects have current heliocentric distance around 40 AU but one object, 2022 FA7, is at ~ 50 AU. In addition to the 17 multi-opposition objects, 7 more single-opposition objects received their provisional designations by Minor Planet Center. This marked the first TNO discovery in South Korea although the telescope itself is located overseas.

How to cite: JeongAhn, Y., Moon, H.-K., Kim, M.-J., and Choi, Y.-J.: Trans-Neptunian Object discoveries at KMTNet-CTIO, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-338, https://doi.org/10.5194/epsc2022-338, 2022.

We have carried out a long term photometric analysis of time series images of the trans-Neptunian object (TNO) 2008 OG₁₉ with which we have refined its physical properties from its long-term variability.

Photometric Analysis

The first detailed analysis of 2008 OG₁₉ was carried out by [1] using rotational light-curves from 2014 and 2016 from which a volume-equivalent diameter, a rotation period (P), a triaxial ellispoidal shape model, and a density were estimated.

We have used 1,314 images covering a time-span of six years (2014-2021), obtained with the Sierra Nevada 1.5-m telescope and the Calar Alto 1.2-m telescope, both in Spain, in order to build yearly rotational light-curves for 2008 OG₁₉. To refine the rotation period estimation of 2008 OG₁₉, we have combined the whole set of data and applyed the lomb periodogram [2] and the Phase Dispersion Minimization techniques [3] resulting in P = 8.72565 +/- 0.0008 hr. The resulting rotational light-curve can be seen in Figure 1.

Long-term variability

By folding the light-curves with the refined period, we have been able to see an increase of the amplitude of the rotational light-curve. This increase is due to a change in the aspect angle, that allows to estimate the orientation of 2008 OG₁₉ rotational axis as seen in Figure 2. Using the largest rotational light-curve amplitude and assuming hydrostatic equilibrium we have updated its triaxial ellispoid model and its density.

Figure 1: 2008 OG₁₉ rotational light-curves folded to P = 8.72565 h. Observational data are represented by color points with each color indicating a different observational night. The black dashed line represent the Fourier series fit.

Figure 2: Model of the amplitude given by the fit to the observational data using b/a = 0.643 in blue (best fit). Other pole solutions are possible with different values of the b/a such as the red model. The gray line represents 2008 OG₁₉ aspect angle given by the best fit. The magenta points with error bars are the observational data from this work.

References
[1] E. d. M. Fernández-Valenzuela, Physical properties of transneptunian objects and centaurs; Ph.D. thesis, University of Granada, Spain, 2017.
[2] N. R. Lomb, Least-squares frequency analysis of unequally spaced data, Astrophysics and Space Science 39 (1976) 447–462. doi:10.1007/BF00648343.
[3] R. F. Stellingwerf, Period determination using phase dispersion minimization, ApJ 224 (1978) 953–960. doi:10.1086/156444.2

How to cite: Costa-Sitjà, M., Fernández-Valenzuela, E., Ortiz, J. L., Morales, N., Santos-Sanz, P., and Vara-Lubiano, M.: Long-term photometric analysis of the trans-Neptunian object 2008 OG19, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-610, https://doi.org/10.5194/epsc2022-610, 2022.

Hi’iaka is the largest satellite of the dwarf planet Haumea, with an estimated area-equivalent diameter of 300 km (Fernández-Valenzuela et al., 2021). It is the best studied satellite in the trans-Neptunian region. Its rotational light-curve was observed with Hubble, for which an approximate rotation period of 9.8 h was obtained (Hastings et al. 2016). The system is very peculiar because it stands out from all other TNO-binary systems. While all other known satellites are thought to be synchronous, Hi’iaka’s rotation period is fast compared to the 49 days that takes to complete an orbit around Haumea. Therefore, the study of Haumea-Hi’iaka system yields important information about the formation processes of the whole Haumea’s system, which includes another moon (Brown et al. 2006), a ring (Ortiz et al. 2017) and a family of objects (Brown et al. 2007).

Our group has been observing Haumea since its discovery, compiling a large database of images since around 20 years ago. Using this set of images we have obtained high accuracy astrometric measurements of the photocenter of the Haumea-Hi’iaka system. We have applied a similar procedure as in Ortiz et al. (2017) to disentangle the position of Haumea from the contribution of Hi'iaka, but for a much larger time span as mentioned above. Therefore, we have been able to determine more accurate orbits for Haumea and Hi'iaka.

Additionally, we have carried out two specific observational runs of several days in order to obtain the rotational phase of Hi’iaka at that moment of the two stellar occultations that occurred last year (in April 2021). We used the 1.23-m telescope at Calar Alto Observatory, the Artemis telescope at Teide Observatory and the 1.5-m telescope at Sierra Nevada Observatory to acquire images of the unresolved system. The resulting photometry of these images give rise two rotational light-curves of Haumea in 2021 and 2022. We fitted a fourth-order Fourier function, which represents Haumea’s body-shape contribution to the rotational light-curves. From this fit, we took the residuals of the observational data and searched for periodicities within them. We obtained a rotation period in agreement with the estimations in Hastings et al. (2016), but much more accurate. These residuals, when folded to the resulting period, provide Hi’iaka’s rotational light-curve. The amplitude obtained for Hi’iaka’s rotational light-curve is 0.015 mag, which agrees with the expected signal induced in Haumea’s rotational light-curve when accounting for a variable source as that produced by Hi’iaka, i.e., considering the rotational light-curve obtained in Hastings et al. (2016). We have not detected a change in the amplitude of Hi’iaka’s rotational light-curve when comparing our data, taken in 2021 and 2022, with those from Hastings et al. (2016), taken in 2010. This means that the obliquity of Hi’iaka must be close to 90º in its orbit around Haumea.

Brown et al. (2006), The Astrophysical Journal, Volume 639, Issue 1, pp. L43-L46.

Brown et al. (2007), Nature, Volume 446, Issue 7133, pp. 294-296.

Fernández-Valenzuela et al. (2021), AAS Division of Planetary Science meeting #53, id. 503.05. Bulletin of the American Astronomical Society, Vol. 53, No. 7 e-id 2021n7i503p05.

Hastings et al. (2016), The Astronomical Journal, Volume 152, Issue 6, article id. 195, 12 pp.

Ortiz et al. (2017), Nature, Volume 550, Issue 7675, pp. 219-223.

How to cite: Fernández-Valenzuela, E., Ortiz, J. L., Morales, N., Jehin, E., Burdanov, A., de Wit, J., Ferrais, M., Vara-Lubiano, M., Morales, R., Kretlow, M., Santos-Sanz, P., Alvarez-Candal, A., Duffard, R., Pál, A., Kiss, C., and Szakáts, R.: Hi’iaka’s physical and dynamical properties using long-term photometric data, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-406, https://doi.org/10.5194/epsc2022-406, 2022.

Centaurs and trans-Neptunian objects (TNOs) are considered to be among the most pristine members of our solar system and carry plenty of information on the physical and dynamical processes that shaped our solar system.

Here we report the occultation observation of the star Gaia EDR3 133768513079427328 (G: 11.7 mag, R: 11.3 mag) by the TNO (119951) 2002 TC302 on November 11, 2021. The shadow path was predicted to cross central Europe and USA. We received a total of 57 observations reports, with at least 19 positive detections and 25 miss reports (no event detected).

2002 TC302 is a high-inclination (i ~ 35°) TNO in a 2:5 resonance with Neptune, orbiting the Sun in an average distance of about 55 au. The radiometric diameter from Herschel and Spitzer thermal observations is 584.1 (+106.5, -88.0) km [1], while the analysis of a multi-chord stellar occultation observed on 28 January 2018, combined with light curve data, revealed an area-equivalent diameter of 499.6 ± 10.2 km [2]. From our preliminary elliptical profile fit of the 11 November 2021 occultation observations we derived a projected area-equivalent diameter of 500.3 ± 2.5 km, which is consistent with the above mentioned value from the previous stellar occultation in 2018. The 2018 and 2021 occultation diameters are significant (about 84 km) smaller than the radiometric diameter, which might be even larger (D ~ 643 km) after a reanalysis of the Herschel data [3]. This discrepancy might indicate the existence of an unresolved satellite, but other possibilities are being considered as well [see also 2,3].

Acknowledgments: We acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). Funding from Spanish projects PID2020-112789GB-I00 from AEI and Proyecto de Excelencia de la Junta de Andalucía PY20-01309 is acknowledged. Part of the research leading to these results has received funding from the European Research Council under the European Community’s H2020 (2014-2020/ERC Grant Agreement no. 669416 “LUCKY STAR”). M.V-L. acknowledges funding from Spanish project AYA2017-89637-R (FEDER/MICINN). P.S-S. acknowledges financial support by the Spanish grant AYA-RTI2018-098657-J-I00 “LEO-SBNAF”.

References
[1] S. Fornasier, E. Lellouch, T. Müller, et al., A&A, 555 (2013) A15.
[2] J. L. Ortiz, P. Santos-Sanz, B. Sicardy, et al., A&A, 639 (2020) A134.
[3] J. L. Ortiz, and the 20-coauthor team, EPSC2020-686, https://doi.org/10.5194/epsc2020-686, 2020.

How to cite: Kretlow, M., Ortiz, J. L., Sicardy, B., Braga-Ribas, F., Desmars, J., Fernández-Valenzuela, E., Morales, N., Santos-Sanz, P., Kilic, Y., Morgado, B., Benedetti-Rossi, G., Camargo, J., Rommel, F. L., Vara-Lubiano, M., Duffard, R., Assafin, M., Ramos Gomes Júnior, A., Souami, D., Vieira-Martins, R., and Álvarez-Candal, Á. and the 2002 TC302 occultation team: The 11 November 2021 multi-chord stellar occultation by trans-Neptunian object (119951) 2002 TC302, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-172, https://doi.org/10.5194/epsc2022-172, 2022.

The discovery of long period comet C/2014 UN271 (Bernardinelli-Bernstein) announced in June 2021 quickly suggested an inactive nucleus with an absolute magnitude of H_V = 7.8 mag [1], which implied a diameter between 130 and 260 km assuming geometric albedos between 2% and 8%. Immediate follow-up observations with our Las Cumbres Observatory (LCO) Outbursting Objects Key project (LOOK) [2] as well as with SkyGems Namibia [3] revealed that the comet was active at 20.18 au. Evidence was quickly found that C/2014 UN271 had been active since 2018 and possibly even active at the time it was first observed in 2014 (at 29 au) [4,5]. After the discovery announcement, follow-up observations with ALMA and HST determined that Bernardinelli-Bernstein has a cometary albedo (0.033 ± 0.009) and an effective diameter of 137 ± 17 km, distinguishing it as the largest observed Oort-cloud comet [6,7].

Prior to the observations of C/2014 UN271, the most distant comet discoveries were C/2010 U3 and C/2017 K2, which were made between 15 and 20 au, but for which pre-discovery images indicate activity beyond 20 au [8,9]. C/2014 UN271 was significantly brighter than those comets at the same distance, which provided an exceptional opportunity to characterize its very distant comet activity close to 20 au. In this presentation we will report the results of our observing program with FORS2 on ESO’s 8-meter VLT in July and August 2021. The VLT/FORS data are interpreted in combination with targeted observations with the 4.1-m SOAR and the long-term monitoring campaign with 1-m facilities within the LOOK Project [10,11]. 

The multi-facility long-term photometric monitoring of C/2014 UN271 enabled our team to identify three outbursts between June and September 2021, indicating that the comet's optical brightness was dominated by cometary outbursts during the VLT observing run. Our VLT/FORS2 multi-band imaging and spectroscopic observations allowed us therefore to characterize the comet’s outburst in terms of spectral slope and coma morphology, including arc-like features. We will also present our efforts to characterize the comet’s short-term variability and rotation period.  

References: [1] https://minorplanetcenter.net/mpec/K21/K21M53.html [2] Kokotanekova, R., et al. (2021), ATel, 14733 [3] https://minorplanetcenter.net/mpec/K21/K21M83.html [4] https://minorplanetcenter.net/mpec/K21/K21M83.html [5] Farnham, T. (2021), ATel, 14759 [6] Lellouch, E. et al. (2022) A&,659, L1, 8 [7] Hui, M.-T., et al. (2022) ApJL, 929, 1, L12, 7 [8] Hui, M.-T., et al. (2019) AJ 157 [9] Jewitt, D. et al. (2021) AJ 161, 188 [10] Lister et al., submitted [11] Kelley et al., submitted.

How to cite: Kokotanekova, R., Kelley, M. S. P., Holt, C. E., Opitom, C., Protopapa, S., Knight, M. M., Lister, T., Bannister, M. T., Snodgrass, C., and Fitzsimmons, A.: Observations during a 20-au outburst of the largest observed Oort-cloud comet C/2014 UN271 (Bernardinelli-Bernstein), Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-989, https://doi.org/10.5194/epsc2022-989, 2022.

Introduction

Comets are the leftovers from the formation of the Solar System. Understanding their composition allow us to investigate the physical and chemical processes occurring at the early stages of its formation. In this contribution we analyze high resolution spectra of comet C/2020 F3 (NEOWISE) obtained with the High Accuracy Radial Velocity Planet Searcher (HARPS-N) echelle spectrograph at the 3.6 m Telescopio Nazionale Galileo (TNG). C/2020 F3 was discovered on 27 March 2020 as a long-period comet, the brightest one observed in the northern hemisphere since the Hale-Bopp in 1997. Its remarkable brightness offered a unique opportunity to investigate its composition through high-resolution spectroscopy, which is otherwise challenging on these targets due to their usual faintness. Our observations already allowed the identification of 4488 cometary emission lines belonging to C2, C3, CN, CH, NH2, Na I and [OI] [1]. We here follow up the molecular identifications by characterizing the gaseous environment of C2020/F3 through the analysis of the molecules’ production rates.

Dataset and Methods

We analyze one HARPS-N spectra of C/2020 F3 obtained on 26 July, at a heliocentric distance of 0.72 AU, covering the wavelengths between 383-693 nm at a spectral resolving power of 115000. We reduced the spectrum by performing absolute calibration, sky subtraction and dust-continuum normalization using IRAF routines and observations of the spectrophotometric standard HR5501 and the solar analog Land 107-684. The calibrated spectra were used in combination with the identified line identification [1] to measure the fluxes of given bands of molecules CN (388.3 nm band), C₂ (516.5 nm band), C₃ (405.0 nm band), NH₂ (577.4 nm band) and OI (630.0 nm line). For each emission line or band, the flux was measured in IRAF through a fit of multiple gaussian profiles, centered at the catalog wavelengths. Cometary production rates are then estimated using a Haser model [2] which parameters were derived from literature studies (e.g., [3])

Results

We estimate production rates of Q[CN]=2.2*10²⁶ , Q[C₂]=2.28*10²⁶ , Q[C₃]=2.15*10²⁷ and finally Q[NH₂]=1.08*10²⁷ . We estimate a H₂O production rate of Q[H₂O]=2.89*10²⁹ , using the OI emission line at 630 nm, therefore assuming that all the flux of this line comes from dissociation of water. Our estimate is in agreement with independent estimates from the SOHO/SWAN instrument[4]. A detailed analysis of the production rate and their comparison with other comets will be presented at the conference.

References

[1] P.Cambianica, et al., 2021, A&A, 656, A160.

[2] Haser, L. 1957Bull. Soc. R. Sci. Liege, 43 (1957), pp. 740-750

[3] Langland-Shula, L., Smith, G. H.,2011, Icarus, Volume 213, Issue 1, 2011, 280-322, 0019-1035

[4] M. R. Combi et al 2021 ApJL 907 L38

How to cite: Munaretto, G., Cambianica, P., Cremonese, G., Fulle, M., Boschin, W., Di Fabrizio, L., Harutyunyan, A., Podio, L., and Codella, C.: Production rates of comet C2020/F3 (NEOWISE) from high resolution spectroscopy, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-360, https://doi.org/10.5194/epsc2022-360, 2022.

Comet NEOWISE (C/2020 F3) displayed a highly structured dust tail, exhibiting the most prominent dust tail features visible from Earth since Comet McNaught (C/2006 P1) in the Southern Hemisphere and Comet Hale-Bopp (C/1995 O1) in the Northern Hemisphere. Using images taken by the amateur astronomer community, this dust tail is analysed using the Finson-Probstein model. The comet’s position in the sky in amateur images is calculated using an open source algorithm [1], the position and exact time then calculated, and the dust tail is simulated. This modelled dust tail structure is then projected and overlaid onto the comet image to directly compare and identify similarities and discrepancies between the model and the image. Using the novel analysis method of mapping the image to a plot of dust grain beta against ejection time[2], tail structures can be more easily identified, analysed and tracked over time (where beta is the ratio of force due to solar radiation pressure and that due to the sun’s gravity).

Dust tail structures such as syndynic bands and striae (near-parallel linear features) have been identified and characterised in terms of dust ejection time and dust beta values. These structures are tracked over time, and compared to the analysis of similar structures seen in C/2006 P1 (McNaught) [2]. There are some clear differences between the two comets, particularly in the alignment and arrangement of their striae, most likely due to different heliospheric conditions during each comet’s perihelion passage.   

These results, all based on amateur observations, provide a thorough description of Comet NEOWISE’s dust tail to contribute to the collection of cometary dust tail profiles currently available. This will enable convenient comparison between comets in the future, and will eventually enable population studies on cometary dust tails and their features. Due to the comet’s very high activity, it also exhibited a rarely seen tail of neutral sodium atoms. This sodium tail has also been parameterised in this work, with an estimated ionization lifetime of the sodium atoms of 17 hours ± 2 hours.

[1] Lang, Dustin, David W. Hogg, Keir Mierle, Michael Blanton, and Sam Roweis. 2010.”Astrometry.net: Blind Astrometric Calibration of Arbitrary Astronomical Images”. The Astronomical Journal 139 (5): 1782-1800. doi:10.1088/0004-6256/139/5/1782.

[2] Price, Oliver, Geraint H. Jones, Jeff Morrill, Mathew Owens, Karl Battams, Huw Morgan, Miloslav Drückmuller, and Sebastian Deiries. 2019. "Fine-Scale Structure In Cometary Dust Tails I: Analysis Of Striae In Comet C/2006 P1 (Mcnaught) Through Temporal Mapping". Icarus 319: 540-557. doi:10.1016/j.icarus.2018.09.013.

How to cite: Afghan, Q., H. Jones, G., Price, O., and J. Coates, A.: Structural analysis of the dust tail of Comet NEOWISE (C/2020 F3), Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-895, https://doi.org/10.5194/epsc2022-895, 2022.

We will present our observations of the bright comet C/2021 A1 (Leonard) with the newly upgraded CRIRES+ high resolution IR spectrometer mounted on the ESO VLT in Paranal, Chile. C/2021 A1 is a long period comet that reached perihelion on January 3, 2022, at 0.62 AU from the Sun. It is one of the brightest comet of recent years, reaching a visual magnitude of 3 close to perihelion (Seiichi Yoshida's webpage).

Originating from the cold Oort Cloud were it spent most of its dynamical lifetime, C/2021 A1 has presumably experienced little transformation or activity, keeping a pristine memory of the chemistry of the protoplanetary disk at the place where it formed. The sublimation of the nucleus volatile ices during its close approach to the Sun was an unique opportunity to have a glimpse at C/2021 A1 composition through the fluorescence of the species in its coma. We observed the comet with CRIRES+ for three nights close to its perihelion at 0.62 AU between December 28, 2021, and January 3, 2022, and derived the production rates of several parent volatiles including H₂O, CH₄, C₂H₆, H₂CO and CH₃OH. During the period of observation, the proximity to the Sun triggered a series of outbursts in C/2021 A1 (Jehin et al, 2022), enhancing the release of material in the coma and ultimately leading to the disintegration of the comet. The observations were made nodding on sky to subtract telluric features in the spectra, and the spectra were later corrected for atmospheric absorption (dominant in the NIR region) and wavelength calibrated by an atmospheric transmittance model computed with the ESO MOLECFIT software (Smette 2015). A flux reference star was also observed to calibrate the target's flux. The chemical composition of the comet will be compared to other comets from the same and other dynamical groups. The ongoing effort to build a chemical taxonomy of comets (A’Hearn et al., 1995; Dello Russo et al., 2016; Lippi et al., 2021) and compare it to the established dynamical classification underlies the need to better constrain the chemical composition of an increasing number individual comets. 

The high resolution IR spectrometer CRIRES+ is an upgrade of the CRIRES spectrometer into a cross-dispersed spectrograph, increasing the simultaneously covered wavelength by a factor 10 (Dorn et al, 2020). It has been available at the VLT since October 2021, offering a resolving power up to 100000 with a 0.2'' slit between 1 and 5 µm. This first observation of a comet with CRIRES+ will also serve to demonstrate its capabilities to target such objects in the IR.

How to cite: Vander Donckt, M., Lippi, M., Faggi, S., and Jehin, E.: The NIR chemical composition of C/2021 A1(Leonard) at perihelion from CRIRES+ at the VLT, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-685, https://doi.org/10.5194/epsc2022-685, 2022.

As the solar wind encounters a comet, ionized gas released from the nucleus propagates away from the Sun with the wind, forming the ion tail of the comet that can stretch for multiple astronomical units. The transport of cometary material antisunward of the comet provides opportunities to measure the cometary composition and plasma interactions at a significant distance from a comet’s nucleus. Serendipitous crossings by spacecraft of comets’ ion tails is a surprisingly commonplace occurrence, but can go unnoticed, as any measured plasma fluctuations can be small.

Using the measured flow of the solar wind at the spacecraft, we can estimate the motion of the solar plasma upstream of the spacecraft, and compare this trajectory with the locations of known comets. This method can uncover previously unnoticed ion tail encounters and predict future encounters.

In December 2021, while comet C/2021 A1 (Leonard) traversed the ecliptic plane, sunward of the spacecraft Solar Orbiter, the spacecraft was immersed in the comet’s ion tail. This encounter was predicted using a range of estimated solar wind velocities to estimate the motion of solar wind plasma to the spacecraft. A wealth of data was collected during the encounter, including results from multiple instruments that support the prediction. We present data returned from the SWA and magnetometer instruments, providing information on the structure of the induced magnetotail. Additionally, images of comet Leonard’s ion tail from other spacecraft during the encounter provide a uniquely complete picture of the tail crossing.

Fig: Orbital configuration of comet Leonard and Solar Orbiter on 18th December 2021, during which Solar Orbiter was immersed in the ion tail of comet Leonard. 

How to cite: Grant, S., Jones, G., Owen, C., and Matteini, L.: The Prediction of, and Results from Solar Orbiter's encounter with Comet C/2021 A1 (Leonard)., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1106, https://doi.org/10.5194/epsc2022-1106, 2022.

1. Introduction

C/2016 R2 (PanSTARRS) was a surprising comet. Detected on September 7, 2016 by Pan-STARRS it showed an unusual composition when it became a bright comet at the end of 2017 and the beginning of 2018. It developed a coma at large (~6 au) heliocentric distance and observations showed that it had a highly unusual composition: no water molecules (or OH radical) could be detected, and the abundances of the usual radicals (CN, C₂, C₃) were unusually low, with a surprising coma composition dominated by CO, CO₂ and N₂ molecules with bright CO⁺ and N₂⁺ emission lines in the visible range. A high CO production rate of about 10²⁹ molecules s^-1 was measured (Biver et al. 2018; Wierzchos & Womack 2018) as well as a high CO₂ production rate (CO₂/CO=1.1 from Opitom et al. 2019), and a high ratio N₂/CO varying between 0.06 and 0.09 (Biver et al. 2018; Cochran & McKay 2018a,b; Opitom et al. 2019; Venkataramani et al. 2020).

The detection of such bright N₂⁺ emission lines in this comet highlighted the necessity of a good modeling of the N₂⁺ fluorescence spectrum in comets. The high-quality spectra published by Opitom et al. (2019) provided a good opportunity to test such a model. This model also permits to compute the fluorescence spectrum of the ¹⁴N¹⁵N⁺ species, leading to the possibility of future measurements of the ¹⁴N/¹⁵N isotopic ratio in the N₂ molecules, one of the main constituant of the solar nebula.

2. Observations

The spectra used for this work have been obtained with the UVES spectrograph mounted on the ESO 8.2 m UT2 telescope of the VLT. Three different observing nights have been used, corresponding to February 11, 13 and 14, 2018. One single exposure of 4800 s of integration time was obtained during each night and we used a 0.44” wide slit, providing a resolving power R~80,000. The slit length was 8” corresponding to about 14,500 km at the distance of the comet (geocentric distance of 2.4 au). The average heliocentric distance was 2.76 au. Opitom et al. (2019) describe in more details the data processing.

From the 2D spectra having a spatial extension of 30 rows, each of them corresponding to a different cometocentric distance, we extracted different 1D spectra for each night. These spectra were then averaged for similar cometocentric distances allowing a detailed comparison of these spectra at different cometocentric distances, the furthest one corresponding to 2x4 rows at the two extremities of the slit (i.e. at a cometocentric distance varying between 4800 and 6600 km).

3. Modeling the N₂⁺ fluorescence spectrum

We developed a new fluorescence model for modeling our observational spectra. The transition involved in this spectrum is the first negative group, i.e. the B²Σ_u⁺ → X²⁺Σ_g⁺ electronic transition with the (0,0) bandhead appearing near 3914 Å. We considered the first three vibrational levels (v = 0; 1; 2) for both X²⁺Σ_g⁺ and B²Σ_u⁺ state, each of them with all the rotational levels from N = 0 to 40.

N₂⁺ having no permanent dipole moment, the pure rotational and vibrational transitions are forbidden (or have a very low probability, through quadrupolar transitions, not taken into account in our model). For that reason it takes a long time for this species to reach its fluorescence equilibrium because it needs a few tens of absorption / emission cycles between the X²⁺Σ_g⁺ and B²Σ_u⁺ states to reach this equilibrium. A comparison of the spectrum obtained on the nucleus with the one obtained at the edges of the slit revealed clear differences due to different rotational relative populations. For that reason we decided to model the N₂⁺ fluorescence spectrum with a Monte-Carlo simulation. Such a computational method allows to compute a spectrum at different times from an initial relative population distribution. Our model starts with a Boltzmann relative population distribution of 80 K (representing an estimate of the kinetic temperature in the inner coma) and uses 10,000 s of evolution time.

We managed to explain satisfactorily the observed N₂⁺ emission spectrum. Fig. 1 presents a close up view around the (0,0) bandhead. This work, presented in more details in Rousselot et al. (2022) also allowed to compute accurate fluorescence efficiencies.

Figure 1: Comparison of the observed VLT UVES spectrum of comet C/2016 R2 (blue) obtained at the ends of the slit with our N₂⁺ model (red).

4. ¹⁴N¹⁵N⁺ fluorescence spectrum

Our modeling of the N₂⁺ fluorescence spectrum can be used to compute the ¹⁴N¹⁵N⁺ fluorescence spectrum, leading to the possibility of measuring the ¹⁴N/¹⁵N isotopic ratio in N₂ molecules. We will present such a spectrum as well as a search for this isotopologue in the C/2016 R2 spectra. Such comets are rare but future observations will reveal other comets similar in composition to C/2016 R2. With future observing facilities now under construction (such as the ESO ELT) ¹⁴N/¹⁵N measurements for N₂ molecules will probably become possible, leading to new constraints on this isotopic ratio.

References

Biver N., et al., 2018, A&A 619, A127

Cochran A. L. & McKay, A. J. 2018a, ApJ, 856, L10

Cochran A. L. & McKay A. J., 2018b, ApJ, 854, L20

Opitom C., et al. 2019, A&A, 624, A64

Rousselot P., et al., 2022, A&A, in press

Venkataramani K., et al., 2020, MNRAS, 495, 3559

Wierzchos K. & Womack M. 2018, AJ, 156, 134

How to cite: Rousselot, P., Anderson, S., Alijah, A., Noyelles, B., Jehin, E., Hutsemékers, D., Opitom, C., and Manfroid, J.: Modeling of N2+ and 14N15N+ fluorescence spectrum in comets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-596, https://doi.org/10.5194/epsc2022-596, 2022.

Introduction: Radio observations of long-period comet C/2016 R2 (PanSTARRS) revealed that it was remarkably depleted in water (Biver et al. 2018). The spectrum was instead dominated by bands of CO⁺ and N₂⁺, rarely seen in such abundance in comets before (Cochran & Mckay 2018). Understanding the nature of this comet would allow us to investigate key features in the timeline of planetesimal formation.

By measuring the observed emission fluxes of the observed N₂⁺ in C/2016 R2's spectrum, ionic ratios of N₂⁺/CO⁺ in the coma were estimated to be between 0.06 (Cochran & Mckay. 2018), Opitom et al. 2019) and 0.08 (Biver et al. 2018). This would be the same ratio for N₂/CO since ionization efficiencies of N₂ and CO are similar at 1 au for quiet Sun (Huebner et al. 1992).

C/2016 R2 provides a unique opportunity to set a baseline for identifying N₂ in cometary spectra. By using the Ultraviolet-Visual Echelle Spectrograph (UVES) mounted on the 8.2 m UT2 telescope of the European Southern Observatory Very Large Telescope (ESO VLT) observations, we can constrain the properties of N2 in the cometary coma and establish new Haser scalelengths in order to determine the N2 production rate, which we present here.

Observations: The observations of C/2016 R2 used in our work were collected on 2018 February 11, 13, and 14 with UVES. All observations were made when the comet was near its perihelion distance of 2.6 au, at 2.76 and 2.75 au. A full description of the observations and data reduction can be found in Opitom et al. (2019).

Methods: We aim to fit the observed flux with a Haser profile (Haser (1957)), providing an analytical solution to the column density of parent- and daughter-species in the coma along the line of sight. N₂⁺ being an ion, the Haser model will be restricted to an area near the coma. The UVES slit covers ~6500 km on either side of the nucleus, a narrow region in which ions should be undisturbed by the solar wind.

CN scalelengths and Production Rate: We first fit a Haser profile on the CN emissions to ensure scalelengths can properly be determined from our data. We created a synthetic CN model evaluated by interpolation from a spectrum calculated by Zucconi (1985). This model is then convolved by the response of our instrument, with an FWHM of 0.06 Å. For each night of 11, 13, and 14 Feb, the CN lines are identified and summed along the spectroscopic slit. The total flux measured for CN over the entire spectrograph and averaged over the three nights of observation was 2.1x10^-15 erg/s/cm2. The flux intensities are then averaged again over their cometocentric distances so as to allow for a proper fit of the Haser model.

By using a X² test, we estimate the best fit of the Haser model to the observed intensity profile and determine the scalelengths of both the parent- (HCN) and daughter- (CN) species in the coma of C/2016 R2. We found l_p = 1.3 x 10⁴ km and l_d = 2.8 x 10⁵ km (scaled to 1 au using an rh2 law) as shown on Fig. 1. With g = 3.52 x 10^-2 photons/s/molecule at 1 au (Schleicher et al. 2010), we estimate a production rate of Q(CN) = (9.8±0.5) x 10²⁴ mol/s.

N2+ scalelengths and Production Rate: The production rate was estimated via relative ratios with g =7 x 10^-2 photons/ion/s from Lutz et al. (1993) by Wierzchos (2018) as Q(N2) = (2.8 ±0.4) x 10²⁷ mol/s and by McKay (2019) as Q(N2) = (4.8 ± 1.1)x10²⁷ mol/s. It can be inferred from Biver et al. (2018) to be ~8.5 x 10²⁷ mol/s for a Q(CO) = 1.1 x 10²⁹ mol/s. These results are first re-calculated with the most recent g factor from Rousselot et al. 2022. With g =4.90 x 10^-3 photons/mol/s at 1 au, prior measurements of the N₂⁺ production rates become Q(N₂) = 4.6x10²⁷ mol/s (Wierzchos & M. Womack 2018), =8.0x10²⁷ mol/s (McKay et al. 2019), and 1.4x10²⁸  mol/s (Biver et al. 2018).

We limit the identification process to the 3885.5 Å to 3915.0 Å interval to further avoid contamination by the CN emission lines. We explore this interval with the X² test and find new scalelengths of l_p = 2.8 x 10⁶ km and l_d = 3.8 x 10⁶ km scaled to 1 au (see Fig. 1). These values are within the expected range estimated from the rate coefficients. However, at this scale, multiple pairs of scalelengths could be selected for N2+ with an equally good fit. We thus have a large uncertainty on the production rate.

Using g = 5.41 x 10^-3 photons/mol/s (at r_h) for the (0,0) band between 3885.5-3915.0 Å and FTOT = 1.0 x 10^-14 erg/s/cm², we find Q(N₂)=(8 ±1) x 10²⁷. With Q(CO) ~ 1.1 × 10²⁹ molecules.s^-1, N2/CO = 0.07, consistent with observed intensity ratios.

Figure 1: The best fit of the Haser model for CN (top, purple, compared to other fits using scalelengths from literature) and N2+ (bottom, blue).

References

A’Hearn et al., 1995) ICARUS 118, 223A

Biver N., et al., 2018, A&A 619, A127

Cochran A. L. & McKay, A. J. 2018a, ApJ, 856, L20

Cochran A. L. & McKay A. J., 2018b, ApJ, 854, L10

Haser L., 1957, BSRSL 43 740H

Huebner W.F., Keady J.J., & Lyon S.P., 1992, ApSS 195 1H

Lutz B.  et al., 1993, ApJ 03 402-411

McKay A. J., et al., 2019, AJ, 158, 128

Opitom C., et al. 2019, A&A, 624, A64

Raghuram S. et al. 2020, MNRAS 501 3 4035-4052

Rousselot P., et al., 2022, A&A, in press

Schliecher D.G., 2010, AJ 140 973S,

Venkataramani K., et al., 2020, MNRAS, 495, 3559

Wierzchos K. & Womack M. 2018, AJ, 156, 134

Wyckoff S. &  Wehinger P. A. 1976, ApJ 204 604W

Zucchoni J.M. & Festou M.C. 1985, AA 150 180Z

How to cite: Anderson, S., Rousselot, P., Noyelles, B., Opitom, C., Jehin, E., Hutsemékers, D., and Manfroid, J.: The N2 Production Rate in C/2016 R2 (PanSTARRS), Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-538, https://doi.org/10.5194/epsc2022-538, 2022.

I - Introduction

Main Belt Comets (MBCs) display comet-like dust-release while occupying asteroid-like orbits in the Main Asteroid Belt (2AU<a<2.5AU). Asteroids and comets have long been perceived as two very distinct populations, initially formed within and beyond the snowline respectively, then split into separate reservoirs. However, the recent discovery of icy objects in the Main Belt, as well as of other active asteroids and inactive comets, blurs the physical, dynamical and observational boundaries between comets andasteroids and indicates it is rather a continuum.

So far no direct detection of gas has been made due to the low gas production rates in MBCs, but dust features of various strengths have been observed. Several mechanisms unrelated to outgassing can lead to apparent activity in asteroids, such as impacts or rotational instability. Therefore, to be recognised as an MBC, an active asteroid must display recurring activity (a tail and/or coma) during multiple passages at perihelion.

Sonnett et al. (2011) previously estimated the MBC to asteroid ratio to be <1:400 in the Main Belt. So far 8 objects have shown recurring activity, and sublimation is a possible driver of activity for a few more candidates (approximately 20 objects in total) (Jewitt & Hsieh 2022). Hence it is challenging to study and characterize such a small population.

Focusing on the Outer Main Belt (a>2.82AU) where most MBCs are found, Kim et al. (2018) showed that the longitudes of perihelion ϖ of MBCs and MBC candidates known at the time were clustered around that of Jupiter (ϖ_J»15°). They concluded that, if this is a real feature of MBCs, these comets would more likely be discoverable in the northern fall night sky.

II - Methods

Using this hypothesis as a criterion, we conducted an imaging survey to search for new active asteroids and MBCs. We selected a sample of 530 Outer Main Belt asteroids with longitudes of perihelion 0°<ϖ<30, and the activity of which would likely be observable if they were MBCs (apparent magnitude, closeness to perihelion, etc.). These objects were observed between 2018 and 2020 using the Wide Field Camera on the Isaac Newton Telescope (La Palma, Spain) and a Sloan-r filter.

We developed an automated pipeline to reduce and analyse our data using tail and coma detection methods adapted from those developed by Sonnett et al. (2011). The tail detection method aims to detect an excess of brightness in one direction around the asteroid. An example is given in Figure 1. The coma detection method builds a frame-specific Point Spread Function (PSF) using neighbouring stars and an artificial coma-profile, then compares them to the asteroid to look for fuzziness. An example is given in Figure 2.

III – Results and perspectives

We reproduced the statistical study of Kim et al. (2018) taking into account more recent discoveries of active asteroids and MBCs (as summarised by Jewitt & Hsieh, 2022) and report that the clustering of longitudes of perihelion persists, which supports our approach a posteriori.

Out of our 549 observations (some asteroids having been observed multiple times), the pipeline was successfully applied to 291 asteroids that did not have any close neighbouring star biasing the analysis. For the remaining objects the pipeline performed the data reduction and produced deep images of the asteroids that we manually reviewed.

Among our targeted sample of objects, we report no detection of activity from the pipeline, nor from visual inspection of the remaining frames. For comparison, we applied the same procedure to random stars and random asteroids on our frames, and saw no difference in the distributions of activity detection levels. We will present our results and statistical conclusions on the MBC population. In the future, our research group intends to implement a similar pipeline to apply these methods to other data, in particular those from the Vera C. Rubin observatory.

Figures

Figure 1 - a: Asteroid 105073 observed on 10/11/2018. b: Illustration of the tail detection method developed by Sonnett et al. (2011). We compare the median brightness of each red segment to the local background flux (median in the cyan annulus). The top-right diagram represents the relative brightness of the segments. Here, the brightest segment is in the South-West direction. We then perform the same study on neighbouring stars to evaluate whether such brightness levels seem atypical given the quality of the frame. In this example, the asteroid happens to be crossing a background star. The star appears trailed as we stacked multiple exposures, giving it the aspect of a tail.

Figure 2 - Example of the coma detection method adapted from Sonnett et al. (2011), applied to asteroid 105073 observed on 10/11/2018. a: Thumbnail of the asteroid. b: PSF constructed from 12 neighbouring stars. c: Simulated coma profile built by convolving a 1/r profile with the PSF. We then fit a linear mix of the PSF and the coma profile to the image of the asteroid. In this case the best fit had a proportion of coma <10^-4. d: Residue of the fit (image a subtracted to the best fit result).

Acknowledgements

We acknowledge contributions from Alan Fitzsimmons (Queen’s University, Belfast, UK) and Henry Hsieh (Planetary Science Institute, Honolulu, US), as well as observers Richard Smith (Queen’s University, Belfast, UK), Daniel Gardener (Institute for Astronomy, Edinburgh, UK) and Hissa Medeiros (Instituto de Astrofísica de Canarias, Tenerife, Spain).

References

David Jewitt and Henry H. Hsieh. The Asteroid-Comet Continuum. arXiv e-prints, arXiv:2203.01397, March 2022.

Yoonyoung Kim, Youngmin JeongAhn, and Henry H. Hsieh. Orbital Alignment of Main-belt Comets. 50:201.04D, October 2018.

Sarah Sonnett, Jan Kleyna, Robert Jedicke, and Joseph Masiero. Limits on the size and orbit distribution of main belt comets. Icarus, 215:534–546, October 2011.

How to cite: Ferellec, L., Snodgrass, C., and Opitom, C.: A targeted search for Main Belt Comets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-925, https://doi.org/10.5194/epsc2022-925, 2022.

Main-belt comets are objects orbiting in the main belt, they have near-surface ice, supposed to be water ice, and it is surprising, because water ice is unstable against sublimation at the surface temperatures of asteroids at the distance of the main belt. This water content is important to better understand the thermal and compositional history of our Solar System, to place constraints on protosolar disk models, and to probe a potential primordial source of terrestrial water.

The main-belt asteroid 324P/La Sagra has been confirmed as main-belt comet by showing repeated dust emission activity during at least two subsequent perihelion passages. The nature of the dust emission in MBCs suggests that it is most likely driven by the sublimation of water ice.

We present photometric analysis of archival data of the main-belt comet 324P/La Sagra from different telescopes: Canada-France-Hawaii Telescope (CFHT), Very Large Telescope (VLT), Gemini North Telescope, Hubble Space Telescope (HST), New Technology Telescope (NTT), Discovery Channel Telescope (DCT).

We find the absolute R-band total magnitude and the estimated total dust mass of the object to be consistent with published results. We also confirm that the activity during the 2015 perihelion passage has significantly decreased compared to the previous perihelion passage in 2010 (Fig. 1). We analysed data in the period December 2011 - April 2019. We also study the recent activity of the main-belt comet 324P/La Sagra at the 2021 perihelion passage, to search for more changes that should provide insight into the evolution of MBC activity over time. Additionally, we measure the dust trail brightness profile of the main-belt comet 324P/La Sagra. From the debris trail brightness profile, we constrain the size of the largest particles that gas drag is able to lift, which is diagnostic of the sublimation rate. Understanding the ice content of outer main-belt asteroids is crucial to constrain the distribution of volatiles in the early solar system and the formation and subsequent evolution of planetesimals.

Figure 1: Absolute magnitudes measured in the central aperture of 324P as a function of orbital position. Circles refer to our analysis of archival data, while triangles are from the literature. After perihelion, the magnitude stabilises around a constant value (18.4 mag in R-band) near a true anomaly of 120°, indicating that dust production has ceased and that dust has left the immediate environment of the nucleus due to solar radiation pressure. An absolute magnitude of 19 measured at true anomaly of -150° indicates that the nucleus could be strongly elongated and be correspondingly faint during part of its rotational lightcurve.

How to cite: Mastropietro, M., Hsieh, H., Kim, Y., and Agarwal, J.: Activity of the Main-Belt Comet 324P/La Sagra, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-1211, https://doi.org/10.5194/epsc2022-1211, 2022.

How to cite: Kim, Y., Jewitt, D., Agarwal, J., Mutchler, M., Li, J., and Weaver, H.: Active Asteroid P/2020 O1: Constraining the Ice Line in the Main Asteroid Belt, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-28, https://doi.org/10.5194/epsc2022-28, 2022.

The binary main-belt comet 288P is peculiar both because of its comet-like activity and because of its unusual system properties, combining near-equal component sizes with a wide separation of about 100 times the primary radius. The system likely formed by rotational disruption after YORP spin-up and subsequently widened, possibly by radiative or outgassing torques.
We present Hubble Space Telescope data obtained in 2021 while 288P re-approached perihelion and activity re-kindled. The data show a developing dust tail. We constrain the time of activity onset and investigate whether one or both components were active, which is key to understanding whether the splitting was the cause of the activity.

How to cite: Agarwal, J., Kim, Y., Jewitt, D., Mutchler, M., Weaver, H., and Larson, S.: Re-activation of main-belt comet 288P in 2021, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-379, https://doi.org/10.5194/epsc2022-379, 2022.

1. INTRODUCTION

Active asteroids are small solar system bodies, having at the same time the orbital characteristics of asteroids but showing the physical characteristics of comets, including coma and tail-like appearance. A subpopulation of active asteroids that have sublimation as the main source of activity is known as main-belt comets (MBCs, [6]). The MBCs could be a key to tracing the origin and evolution of volatile materials in the asteroid belt and could help our understanding of the protoplanetary disk process and planetary formation. The number of known MBCs is, however, still relatively small. For this reason, the characterisation of new objects is of considerable importance.

This work analyses active asteroid (248370) 2005QN173, (aka 433P). Its activity was recently discovered by Fitzsimmons et al. [4] in the images collected by the Asteroid-Terrestrial-Impact Last Alert System (ATLAS;[11]). Based on the recurrent activity, Chandler et al. [3] suggested that activity is sublimation-driven, making asteroid 248370 a main-belt comet. Aiming to constrain possible activity mechanisms further, we performed photometric observations of 248370. Our primary goals are to quantify the activity level variation and determine the rotation period. The activity changes could help better understand what is driving the activity. Similarly, the rotation period provides a clue on a possible mass shedding due to rotational instabilities. Furthermore, we also analysed its dynamical stability in order to get insights into the past orbit evolution. Finally, we investigated its possible association with asteroid families.

2. OBSERVATIONS

Observations of the 248370 were collected on 2021 October 5/6 from the Astronomical station Vidojevica (C89), using a 1.4 m Milanković telescope. All images were made in standard Johnson-Cousin R-filter.

Figure 1: Field of view for one of the images of the active asteroid 248730.

3. ROTATIONAL PERIOD

Image processing, measurement, light curve construction and period analysis were done using procedures incorporated into the MPO Canopus2 [10]. In particular, the period analysis is performed using the Fourier analysis algorithm developed by Harris et al.[5].

Unfortunately, we were not able to find a unique rotational period solution. Instead, we derived two possible periods of 2.7±0.1 and 4.1±0.1 hours. The corresponding light-curve amplitudes computed after correcting for the effect of coma are 0.28 and 0.58 mag, respectively. An example of the obtained light-curve of 248370, along with a fit corresponding to the period solution of 2.7±0.1 h, is shown in Figure 2.

Figure 2:  The phased plot for the period of 2.7±0.1 h.

We also calculated the rotational fission critical limit for a strengthless triaxial ellipsoid [8] for the light-curve solutions. It turns out that both periods are shorter than the critical limit, suggesting that rotation mass shedding could be partly responsible for the observed activity.

4. ACTIVITY LEVEL

The activity level is constrained by estimating the length of the tail, Ad/An ratio, and Afρ parameter of 248370. The projection of the tail onto the sky, estimated from the composed image, extends approximately 4 arcmins from the nucleus. This length corresponds to a physical extension of about 264,000 km, about a factor 3 shorter than estimated by Hsieh et al. [7] from their observations made closer to the perihelion.

The estimated scattering cross-section of ejected near-nucleus particles and the underlying nucleus is Ad/An = 1.3. It also confirms that the activity level is fading as the object moves further from the perihelion but at a modest rate of only 0.006 mag/day.

Afρ is the ratio between the effective cross-section of comet grains in the field of view and the area of that field [1]. From our observations, we obtained a value of Afρ = 10.8. Compared to the values obtained by Hsieh et al. [7], the parameter has constantly decreased since the perihelion passage. All these findings are consistent with the sublimation-driven activity.

5. DYNAMICAL STABILITY AND ASSOCIATION WITH ASTEROID FAMILIES

The dynamical analysis has shown that 248370 is a dynamically unstable object, residing in 11/5 mean motion resonance with Jupiter. Its Lyapunov time is only about five kyr, further suggesting that the object is highly unstable. This implies that 248370 is not residing at its current orbit for a very long time but instead migrated into the resonance, probably due to the Yarkovsky effect, within the maximum last 100 Myr.

Despite the orbit instability, we found that 248370 likely belongs to the Themis asteroid family, making it possibly a fourth main-belt comet associated with this group. Moreover, 248370 is also within reach of a young sub-family of the Themis family, namely the 288P cluster, which is also associated with its namesake main-belt comet 288P [9].

6. CONCLUSIONS

The level of the activity trend is consistent with sublimation driven activity in active asteroid 248370. However, the most likely spin period solutions are both below the critical limit for rotational mass shedding. Therefore, this mechanism could also play a role in the object’s coma and tail production. This brings some similarities between 248370 and binary MBC 228P [2]. The situation is especially intriguing as the two objects are close in the orbital space and might both originate from the same collisionally disrupted parent body.

REFERENCES

[1] A’Hearn M. F., Schleicher D. G., Millis R. L., Feldman P. D.,Thompson D. T., 1984, AJ, 89, 579

[2] Agarwal J., Kim Y., Jewitt D., Mutchler M., Weaver H., Larson S., 2020, A&A, 643, A152

[3] Chandler C. O., Trujillo C. A., Hsieh H. H., 2021, ApJ, 922, L8

[4] Fitzsimmons A., Erasmus N., Thirouin A., Hsieh H. H., Green D., 2021, Central Bureau Electronic Telegrams

[5] Harris A. W., et al., 1989, Icarus, 77, 171

[6] Hsieh H. H., Jewitt D., 2006, Science, 312, 561

[7] Hsieh H. H., et al., 2021, ApJ, 922, L9

[8] Jewitt D., Weaver H., Mutchler M., Li J., Agarwal J., Larson S., 2018, AJ, 155, 231

[9] Novaković B., Hsieh H. H., Cellino A., 2012, MNRAS, 424, 1432

[10] Warner B., 2021, BDW Publishing

[11] Tonry J. L., et al., 2018, PASP, 130, 064505

How to cite: Novakovic, B., Pavela, D., Hsieh, H., and Marceta, D.: Characterisation of active asteroid (248370) 2005QN173, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-83, https://doi.org/10.5194/epsc2022-83, 2022.

Introduction: Results from the Dawn mission showed us an aqueously altered cryovolcanic world of Ceres, maybe a relict Ocean World [1, 2]. Geological studies suggested brine-driven features, including the cryovolcanic dome Ahuna Mons [3] and the Cerealia and Vinalia Faculae, which are carbonate- and chloride-rich evaporites [4] formed from brine extrusion with evidence of recent activity [5]. In addition, the Haulani crater is among the youngest impact features on Ceres [6], potentially excavating relatively fresh, volatile-rich subsurface materials with distinctly bright and blue spectral characteristics [7]. In this study, we focus on the spectrophotometric properties of the geologically young features, aiming to characterize Ceres’s regolith evolution and better understand the cryovolcanic processes. Here we report the preliminary results of the Haulani crater (latitude  -3º to 14º, longitude 0º to 20º) and Ahuna Mons regions (latitude -17º to -3º, longitude 308º - 322º).

Data: We used the multiband images of Ceres collected by the Dawn Framing Camera with pixel scales <150 m/pixel and calibrated them to radiance factor (RADF) following [8, 9], including infield straylight removal for all color images. The scattering backplanes were calculated with the USGS ISIS software using the high-resolution digital terrain models from the Planetary Data System [10].  The alignment between the backplanes and the corresponding images was checked and adjusted. For each region, we defined four regions of interest (ROIs; Fig. 1) based on the geological context. Our photometric modeling was performed independently for each ROI in each of the seven color filters.

Figure 1. ROI of the Haulani crater region (left) and the Ahuna Mons region (right).

Photometric Modeling: We adopted the five-parameter version of the Hapke model as used by [11]. Without data at phase angles <20º, we assumed an amplitude parameter B0=1.6 and a width parameter h=0.06 for the shadow-hiding opposition effect [12]. The other three parameters, including the single-scattering albedo (SSA), asymmetry factor, g, of the single-term Henyey-Greenstein function for the single-particle phase function, and the roughness parameter are free for fitting. The best-fit model parameters were retrieved in a least-χ² sense following [11]. Fig. 2 shows the spectra of the best-fit parameters. Overall the relative root-mean-squared, which is defined as rel.RMS=√[Σ(r_measure-r_model)²/N]/<r_measure>, with r_measure and r_model being the measured and modeled reflectance, respectively, N being the number of data points, and <r_measure> being the average measured reflectance, is 4-9%, compared to 4-6% of the global model [11], suggesting a reasonably good fit. The similar results for the background ROIs in all bands in the two regions indicate consistent model fitting across all ROIs. However, the 0º roughness parameter retrieved for the Ahuna Mons ROI in some bands is probably problematic, as also indicated by the relatively high model RMS for this ROI.

Figure 2. Modeled Hapke parameters for all ROIs in the Haulani crater region (a) and the Ahuna Mons region (b).

A comparison of all ROIs suggests that: 1) The photometric properties in the Haulani crater region are more diverse than those in the Ahuna Mons region. 2) The albedo spectra of all ROIs show a spectral feature centered in the 750 nm filter with varying characteristics. The nature of this feature is unclear. We further calculated the spectral slopes of the SSA and the g-parameter (excluding 440 nm) to quantify the color and phase reddening of all ROIs.

Conclusion and Discussion: Our results suggest that these ROIs likely form a trend, with the Haulani crater floor and Ahuna Mons as exceptions (Fig. 3). The apparent trendline of roughness vs. SSA is opposite of what was usually observed in asteroids caused by multiple scattering into shadows. What this trend means to Ceres’s regolith is still under investigation. On the other hand, the Haulani crater floor material is clearly below the trendline. Ahuna Mons is below the trendline, but the fitted 0º roughness is dubious. Fig. 3b shows that the trendline is primarily formed by the ROIs in the Haulani crater region. The points of the Ahuna Mons region ROIs cluster near the background. The Haulani crater floor and Ahuna Mons are clearly out of the trendline. Given the much younger geological age of the Haulani crater region of ~2 Ma [6] than that of the Ahuna Mons region (~200 Ma for Ahuna Mons [3], ~600 Ma for Yalode ejecta [13]), if the trendline represents an evolutionary sequence, then the corresponding timescale is around several Ma.

Figure 3. Roughness parameter vs. SSA for all ROIs at all bands (a) and the spectral slope of the g-parameter vs. that of the SSA (b). The dashed lines represent eye-balled trendlines.

We note that our results presented here are preliminary. The statistical significance of the trendline needs to be further accessed from the model uncertainties. But overall, such an evolutionary trend is in line with the previous results about the regolith evolution caused by the devolatilization of ice-rich materials near young craters [14, 15].

Acknowledgments: This research is supported by NASA Grant #80NSSC21K1017 and partially by the SSERVI16 Cooperative Agreement (#NNH16ZDA001N), SSERVI-TREX.

References: [1] Hendrix, A.R., et al., 2019, Astrobiology 19, 1; [2] De Sanctis, M.C., et al. 2020a, SSR 216, 60; [3] Ruesch, O., et al., 2016, Science 353, 1005; [4] Raponi, A., et al., 2019. Icarus 320, 83; [5] De Sanctis, M.C., et al. 2020b, Nature Astron. 4, 786; [6] Krohn, K., et al., 2018, Icarus 316, 84; [7] Schröder, S.E., et al., 2017, Icarus 288, 201; [8] Schröder, S.E., et al., 2013, Icarus 226, 1304; [9] Schröder, S.E., et al., 2014, Icarus 234, 99; [10] Roatsch et al. 2017, DAWN-A-FC2-5- CERESLAMODTMSPG-V1.0, NASA Planetary Data System; [11] Li, J.-Y., et al., 2019, Icarus 322, 144; [12] Helfenstein, P., Veverka, J., 1989, In: Asteroids II, 557; [13] Crown, D.A. et al. 2018, Icarus 316, 167; [14] Stephan, K., et al., 2017, GRL 44, 1660; [15] Schröder, S.E., et al., 2021, Nature Comm. 12, 274.

How to cite: Li, J.-Y., Zou, X.-D., Mest, S. C., Schröder, S. E., Mottola, S., and Kargel, J. S.: Spectrophotometric Properties of Geologically Young Regions on Ceres, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-96, https://doi.org/10.5194/epsc2022-96, 2022.

The COmetary Secondary Ion Mass Analyser (COSIMA) instrument on board ESA's Rosetta mission to comet 67P/Churyumov–Gerasimenko has collected and analysed dust particles in the inner coma from August 2014 to September 2016 between 1.25 and 3.8 AU solar distance and 4 to 1000 km off the comet nucleus. The dust particles were identified with optical microscopy and analysed with secondary ion mass spectrometry (SIMS). The elemental composition of the dust particles collected and analysed with SIMS is heterogeneous for the mineral forming elements within a factor of 2. The potential relation between optical properties and dust particle elemental ratio of carbon and silicon has been studied. 

How to cite: Hilchenbach, M., Stenzel, O., and Fischer, H.: Elemental Composition and Optical Properties of Cometary Dust Particles in the Coma of Comet 67P, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-482, https://doi.org/10.5194/epsc2022-482, 2022.

During the visit of the European Space Agency’s Rosetta mission to comet 67P/Churyumov-Gerasimenko, the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) on the spacecraft took several image sequences of 67P’s nucleus that highlight its activity against the dark backdrop of space. Especially during the later phase of the mission when 67P was outbound from perihelion and its activity ceasing, Rosetta was able to record sequences from less than 100 km away, which resulted in m-sized resolutions at the distance of the nucleus. At this distance, thousands of point-source-like particles can be distinguished from the diffuse coma.

Following Agarwal et al. (2016), who successfully tracked such particles manually, we developed a fully automated tracking algorithm (Pfeifer et al. 2021) which we have now applied to several datasets and performed an in-depth analysis of the results.

We for example selected sub-sets of particles and extrapolated their 2D-trajectories in the image plane back in time to relatively confined areas on the nucleus. Assuming that the particles originated from the identified location and that they have not moved too far away from it, we can estimate their distance to the spacecraft and thus their (projected) dynamics and size distributions.

In particular, we can compare the measured accelerations to a (simplified) version of the particle’s equation of motion:

where ⃗a is the particle acceleration, m_p, the particle mass, ⃗ F_G the nucleus gravity, ⃗ F_D the gas drag, G the gravitational constant, M the nucleus mass, d the particle-nucleus distance, ⃗n_G the gravity unit vector, C_D the drag coefficient, m_g the mass of a water molecule, n_g the gas number density, ρ_p the particle density, ⃗v_g the gas and ⃗v_p the particle velocity, and r the particle radius. By fitting this equation to our data we try to constrain the parameters that go into it.

We present our latest results from tracking mostly dm-sized particles that were recorded by OSIRIS near the surface of comet 67P in December 2015 and January 2016. While the particle dynamics themselves already present new information, the properties that we can derive from them also help us to better understand the gas flow and other circumstances at the time of the observed activity.

Acknowledgements

We acknowledge the operation and calibration team at MPS and the Principal Investigator Holger Sierks on behalf of the OSIRIS Team for providing the OSIRIS images and related datasets. OSIRIS was built by a consortium of the Max-Planck-Institut für Sonnensystemforschung, Göttingen, Germany; the CISAS University of Padova, Italy; the Laboratoire d’Astrophysique de Marseille, France; the Instituto de Astrofísica de Andalucia, CSIC, Granada, Spain; the Research and Scientific Support Department of the European Space Agency, Noordwijk, The Nether- lands; the Instituto Nacional de Técnica Aeroespacial, Madrid, Spain; the Universidad Politéchnica de Madrid, Spain; the Department of Physics and Astronomy of Uppsala University, Sweden; and the Institut für Datentechnik und Kommunikationsnetze der Technischen Universität Braunschweig, Germany. The support of the national funding agencies of Germany (DLR), France (CNES), Italy (ASI), Spain (MEC), Sweden (SNSB), and the ESA Technical Directorate is gratefully acknowledged. We thank the Rosetta Science Ground Segment at ESAC, the Rosetta Missions Operations Centre at ESOC and the Rosetta Project at ESTEC for their outstanding work enabling the science return of the Rosetta Mission.
MP and JA acknowledge funding by the ERC Starting Grant No. 757390 Comet and Asteroid Re-Shaping through Activity (CAstRA). JA acknowledges funding by the Volkswagen Foundation.

References

Agarwal, J., A’Hearn, M. F., Vincent, J.-B., et al. 2016, MNRAS, 462, S78
Pfeifer, Marius, Agarwal, Jessica, & Schröter, Matthias. 2022, A&A, 659, A171

How to cite: Pfeifer, M., Agarwal, J., and Marschall, R.: Dynamics of dm-sized Particles in the Coma of Comet 67P/Churyumov–Gerasimenko, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-814, https://doi.org/10.5194/epsc2022-814, 2022.

Comets are thought to have preserved dust particles from the very beginning of Solar System formation, providing a unique insight into intricate processes like dust growth mechanisms. The Rosetta mission offered the best opportunity to investigate nearly pristine cometary dust particles of comet 67P/Churyumov–Gerasimenko. In particular, among the three in-situ dust instruments, the MIDAS (Micro-Imaging Dust Analysis System) atomic force microscope collected cometary dust particles with sizes from hundreds of nanometres to tens of micrometres on dedicated targets and recorded their 3D topographic information and related parameters (Bentley et al. 2016a). However, the straightforward dust collection strategy, i.e., simply hitting the collection targets, leads to an unknown degree of collection alteration (Mannel et al. 2016; Bentley et al. 2016b).

We aim to understand dust alteration during collection and determine which structural properties of the MIDAS dust particle remained pristine. An exhaustive dust particle catalogue for MIDAS is created, containing 3494 dust particles with (meta)data. Among these particles, we carefully select 1082 particles that are eligible for a more extensive structural investigation. First, we generate sophisticated dust maps showing the distribution of the selected dust particles on the collection targets and investigate dust clustering, i.e., determination of which of the particles stem from a single parent particle that fragmented upon the collection impact. Additionally, in the collaboration with Longobardo et al. in preparation, we use an algorithm to determine from which cometary source regions which MIDAS particles were stemming (Longobardo et al. 2020). Next, we develop MIDAS particle shape descriptors such as aspect ratio (i.e., height of the particle divided by the square root of area; Lasue et al. 2019), elongation, circularity, convexity, and particle surface/volume distribution. Furthermore, we compare the structure of the MIDAS dust particles and the clusters to those found in the laboratory experiments (Ellerborek et al. 2017) and by COSIMA/Rosetta (Langevin et al. 2016). Finally, we combine our findings to calculate a pristinity score for MIDAS particles and determine the most pristine particles and their properties.

Fig 1. 3D dust coverage map of target 13

We find there is only a weak trend between shape descriptors and cometary source regions, cluster morphology, and particle characteristics such as size and particle morphology. For example, particles ejected from smooth or rough terrain are similar in their investigated shape properties, which implies dust particle activity such as dust ejection, partial dry out, and recycled dust material are not responsible for the structure of particles at the micrometre scale. Furthermore, the aspect ratio distributions suggest that the subunits of different cluster types are similar in their shape and composition. Thus, the different cluster morphologies detected by MIDAS are not created by a change in subunit properties, but rather by different impact velocities, a result in good agreement with the finding of laboratory experiments (Ellerbroek et al. 2017) and simulations (Lasue et al. 2019). Next, the types of clusters found in MIDAS show good agreement (Ellerbroek et al. 2017), however, there are some differences to those found by COSIMA (Lasue et al. 2019). Furthermore, our pristinity score shows that almost half of MIDAS particles suffered severe alteration by impact, which indicates dust alteration was inevitable with the given dust collection strategy. Consequently, only ~ 20 particles were rated 'moderately pristine' particles, i.e., they are not substantially flattened by impact, not fragmented, and/or not part of a fragmentation cluster. The microphysical properties of pristine cometary materials are established in this study and can be translated into properties of laboratory analogue materials for future study to understand comets and early Solar System processes.

How to cite: Kim, M., Mannel, T., Lasue, J., Longobardo, A., Bentely, M., and Moissl, R.: Primitiveness of cometary dust collected by MIDAS on-boardRosetta, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-3, https://doi.org/10.5194/epsc2022-3, 2022.

The Rosetta mission to comet 67P/C-G provided a detailed view of the near nucleus environment of an active Jupiter family comet. The continuous monitoring of the gas pressure with the ROSINA experiment at the location of the Rosetta spacecraft in combination with the images of the dust environment acquired by the OSIRIS cameras allows one to test different hypotheses about the origin of the dust and gas emissions. In addition the orbital elements and the rotation axis and spin rate of the nucleus are affected by the gas release.

The dust and gas emission around the nucleus of comet 67P/C-G displays a very repetitive pattern in time and space [1,2], with additional short-lived (< 30 min) localized outbursts of activity, in particular around perihelion [3].

We present an overall assessment of the gas emission of comet 67P/C-G based on (i) connecting the ROSINA gas measurements to surface activity and (ii) based on the observed changes in the orbital and rotational state vector [4,5], including the 2021/22 MPEC data set for the astrometry.

One important tool is our use of a detailed shape-based model to constrain the gas and dust emission. We describe two limiting cases for which analytic solutions of the gas field are obtainable: (1) a rarefied gas emission with non-interacting gas flows and (2) an incompressible flow field. We discuss their implications for the dust lift-off from the surface of the nucleus. We estimate the velocity of the dust propelled by the gas from the Coriolis deflection. The deflection and dust velocity is accessible from the OSIRIS data by looking at the curvature of the observed dust streams.

We systematically discuss uncertainties in the data analysis and point out open questions regarding the choice of boundary and initial conditions for the modeling of the coma around the nucleus. The surface composition of the nucleus in terms of 14 volatiles for 67P/C-G is shown as surface distribution maps [6,7], which provides a baseline for the comparison with other comets and active gas and dust emitting objects.

References:

1. Kramer, T. & Noack, M. On the Origin of Inner Coma Structures Observed by Rosetta during a Diurnal Rotation of Comet 67P/Churyumov–Gerasimenko. ApJL 823, L11 (2016).

2. Kramer, T., Noack, M., Baum, D., Hege, H.-C. & Heller, E. J. Dust and gas emission from cometary nuclei: the case of comet 67P/Churyumov–Gerasimenko. Advances in Physics: X 3, 1404436 (2018).

3. Vincent, J.-B. et al. Summer fireworks on comet 67P. Monthly Notices of the Royal Astronomical Society 462, S184–S194 (2016).1. Kramer, T. & Noack, M. On the Origin of Inner Coma Structures Observed by Rosetta during a Diurnal Rotation of Comet 67P/Churyumov–Gerasimenko. ApJL 823, L11 (2016).

4. Kramer, T. et al. Comet 67P/Churyumov-Gerasimenko rotation changes derived from sublimation-induced torques. Astronomy & Astrophysics 630, A3 (2019).

5. Kramer, T. & Läuter, M. Outgassing-induced acceleration of comet 67P/Churyumov-Gerasimenko. Astronomy & Astrophysics 630, A4 (2019).

6. Kramer, T., Läuter, M., Rubin, M. & Altwegg, K. Seasonal changes of the volatile density in the coma and on the surface of comet 67P/Churyumov–Gerasimenko. Monthly Notices of the Royal Astronomical Society 469, S20–S28 (2017).

7. Läuter, M., Kramer, T., Rubin, M. & Altwegg, K. The Ice Composition Close to the Surface of Comet 67P/Churyumov-Gerasimenko. ACS Earth Space Chem. acsearthspacechem.1c00378 (2022) doi:10.1021/acsearthspacechem.1c00378.

How to cite: Kramer, T. and Läuter, M.: The near nucleus gas and dust environment around comet 67P/Churyumov-Gerasimenko, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-281, https://doi.org/10.5194/epsc2022-281, 2022.

We present the most extensive catalog of exposures of volatiles on the nucleus of  comet 67P/Churyumov-Gerasimenko from observations acquired with the OSIRIS imaging system on board the Rosetta mission.  We have analyzed medium and high-resolution images acquired with the Narrow Angle Camera (NAC) of OSIRIS at different wavelength in the 250-1000 nm range, investigating images from 109 different color sequences taken between August 2014 and September 2016, and covering spatial resolution from a few m/px to 0.1 m/px.

Exposure of volatiles are usually brighter than the comet dark terrain, and characterized by a neutral to moderate spectral slope in the visible range, which has been proven to be associated with a local enrichment in water ice thanks to joint observations carried out with the OSIRIS cameras and the VIRTIS visible and near infrared imaging spectrometer [2]. We applied the following methodology to identified exposure of volatiles on the 67P nucleus: bright spots exposing volatiles should both be brighter (at least 50%) than the comet dark terrain, and should have a neutral to moderate spectral slope values in the visible range (535 -882 nm) range. The spectral slope values has been chosen lower than 12%/(100 nm), but usually bright spots have spectral slope much lower than 8%/(100 nm).

Our analysis considerably expands by a factor of 10 the catalogue of bright spots previously identified (about 70  [1, 2, 3, 4, 5, 6]) on the comet, and produces the most extensive catalogue with more than 700 entries of exposure of  volatiles on 67P nucleus. For each bright spot we compute its surface, its precise location of the nucleus, its spectral slope, and its lifetime, and for some the estimated water ice abundance using geographical mixtures of the comet dark terrain and water ice. This lifetime of bright spots was estimated as the time in which a bright spot remains visible in different observing sequences. This estimation is of course biased by the observing frequency-conditions, thus the real lifetime is usually longer than the one reported. Volatiles may survive exposed to the surface for a period varying from a few days, to several months. Longer durations are usually found for water ice exposed after cliff collapse or formation of new scarps, exposing the underlying water-rich material.

Bright spots could be found isolated on the nucleus surface or grouped in a cluster, usually at the feet of cliffs. Isolated bright spots are observed in different type of morphological terrains, including smooth surface, on the top of boulders or close to irregular structures. Several of them are clearly correlated with the cometary activity, being the sources of jets or appearing after an activity event [7]. Even if numerous bright spots are detected, the total surface of exposed water ice is about 84000 m², that is 0.16% of the total 67P nucleus surface. This confirms that the surface of comet 67P is dominated by refractory dark terrains, while ice only occupies a tiny fraction

We also noticed an evolution of the spectral slope values, with the presence of several bright spots having negative slope only in the post-perihelion images, while during and pre-perihelion slopes values were close to zero or moderately positive. There is also a clear difference in the areal distribution of the bright spots pre- and post-perihelion. While bright spots have a larger median surface of about 5 m² in the pre-perihelion images, most of them have surfaces lower than 1-2 m² post-perihelion, clearly indicating that high spatial resolution is mandatory to identify exposure of volatiles on cometary surfaces. Our results on the bright spots area support the findings of Ciarniello et al. [8] and Fulle et al. [9] who deduced that the bright spots on comets are exposure of the primordial water-ice-enriched blocks (WEB) forming, together with the refractory matrix, cometary nuclei, and whose dominant size is of the order of 0.5-1 m. WEBs should be formed of water ice rich pebbles mixed with drier material, and exposed to the nucleus surface when the cometary activity erodes the dust mantle.

The fact that the majority of the bright spots are sub-meter sized is thus in agreement with

these predictions and with the radar measurements the 67P comet provided by CONSERT, which indicate that the nucleus is homogeneous up to scales of a few meters [10].

References:

 [1] Pommerol et al., 2015, A&A 583:A25; [2] Barucci et al., 2016, A&A 595, id.A102; [3] Deshapriya et al., 2016, MNRAS 462, S274  [4] Fornasier et al., 2016, Science 354, 1566; [5] Deshapriya et al. 2018, A&A 613, id.A36; [6] Oklay et al., 2017, MNRAS 469, S582, [7] Fornasier et al., 2019, A&A 630, A13; [8]  Ciarniello et al., 2022, Nat. Astron. https://doi.org/10.1038/s41550-022-01625-y: [9] Fulle et al., 2020, MNRAS 493, 4039; [10] Ciarletti et al., MNRAS 469, S805

How to cite: Fornasier, S., Hoang, V. H., and Quirico, E.: Extensive catalogue of exposures of volatiles on 67P/Churyumov-Gerasimenko comet nucleus revealed from the OSIRIS cameras onboard the Rosetta mission, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-109, https://doi.org/10.5194/epsc2022-109, 2022.

Introduction

The ESA Rosetta mission orbited the 67P/Churyumov-Gerasimenko comet (hereafter 67P) for two years and its results are providing important clues to understand activity processes on comets.

The goal of the ISSI International Team “Characterization of 67P cometary activity” is two-fold:

• Retrieval of the activity of different regions of 67P’s surface during different time periods.
• Identification of the main drivers and the effects of cometary activity, via revealing the link between cometary activity and illumination/local time, dust morphology and composition, and surface geomorphology.

Goal #1 has been reached by tracing the motion of dust particles detected in the coma back to the nucleus surface.

Goal #2 accomplishment is in progress by means of data fusion of different instruments onboard the Rosetta spacecraft.

Traceback

The Grain Impact Analyser and Dust Accumulator (GIADA) [1] measured speed and momentum of fluffy and compact dust particles. We assumed radial motion, constant dust acceleration up to a 11 km altitude and constant speed above that height, to retrieve the source region of each dust particle detected in the coma [2]. We obtained that fluffy and compact dust distributions correlate on the surface, but not in the coma due to the different speeds of the two dust categories. Dust ejection is also correlated with solar illumination. Fluffy particles are more abundant in rough terrains [3], according to models which predict that they are embedded within pebbles [4].

Traceback is under study also with a different approach, based on retrieving ejection probability maps of detected dust particles [5].

Data Fusion

GIADA vs VIRTIS. We related dust ejection rates of different surface regions, as retrieved by GIADA, and spectral indicators of water ice exposure measured by the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS) of Rosetta, such as the shortward shift of the 3.2 mm absorption band center and infrared spectral slope flattening [2]. The observed correlation between these parameters (Figure 1) indicates that ejection of dust comes from water ice-rich regions.

Figure 1. Observed correlation between number of fluffy particles ejected from each 67P surface region and observed infrared slope flattening. Each symbol identifies a different geomorphological region of 67P.

GIADA vs MIDAS. The Micro-Imaging Dust Analysis System (MIDAS) detected and measured physical properties of micron-sized particles. In principle, it provides complementary information with respect to GIADA, which detected mm-sized particles.

We retrieved the number of parent particles hitting the MIDAS targets by applying two different methods [7,8]. Independently of the used approach, we obtained that the dust flux ratio between the two instruments is temporally constant. This suggests that the small particles detected by MIDAS are fragments of larger particles, as those detected by GIADA.

The combination of MIDAS data and our traceback algorithm revealed that the physical properties (size, density, flatness) of compact dust are homogeneous across 67P’s surface (Figure 2). Indicators of dust pristinity were defined [8] and suggested that pristinity is correlated with size (being small particles more pristine) but not with the ejecting region evolution degree.

Figure 2. Flatness distribution of dust particles detected on different MIDAS target (each target corresponds to a defined exposition period). Distributions are very similar.

GIADA vs ROSINA. ROSINA-COPS (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis - COmetary Pressure Sensor) detected icy particles as pressure peaks [9]. The GIADA-ROSINA data fusion allows us to associate icy and dust particles and to retrieve the icy particle source regions.

Currently, a moderate correlation between icy and dust fluffy dust particles was found. The work is in progress.

Conclusions and future perspectives

. We found that fluffy dust particles are more abundant on rough terrains, in agreement with their lower evolution degree and to comet formation models. Physical properties of compact dust are similar across the comet surface. The relation between dust and icy particles is under study.

Future activities include:

• Analysis of the COSIMA mass spectrometer data [10], which observed dust composition variations. COSIMA-GIADA data fusion will allow understanding if they are related to different surface terrains.
• Analysis of OSIRIS images, which show bright patches on the comet surface, corresponding to frost enrichments and having different composition and morphology [11]. OSIRIS images combined with GIADA and ROSINA data will help in characterizing these peculiar regions.
• Laboratory activity aimed at simulating and interpreting the different photometric behavior of rough and smooth terrains [12] at the dust scale

References

[1] Della Corte, V. et al. (2014), Journal of Astronomical Instrumentation, 3, 1, 1350011-110; [2] Longobardo, A. et al. (2019), MNRAS, 483, 2, 2165-2176; [3] Longobardo, A. et al. (2020), MNRAS, 496, 1, 125-137; [4] Fulle, M. and Blum, J. (2017), MNRAS, 492, 2, S39-S44; [5] Ivanovski, S.L. et al. (2017), EPSC, 708; [6] Bentley, M.S. et al. (2016), Nature, 537, 7618, 73-75; [7] Longobardo, A. et al. (2020), EPSC, 1044; [8] Kim, M. et al. (2022), EGU abstract; [9] Pestoni, B. et al. (2022), EPSC, this session; [10] Hilchenback, M. et al. (2019), EPSC, 900; [11] Dehapriya, J.D.P. et al. (2018), EPSC, 1166; [12] Longobardo, A. et al. (2017), MNRAS, 469, 2, S346-S356.

Acknowledgements

This research was supported by the Italian Space Agency (ASI) within the ASI-INAF agreement I/032/05/0 and by the International Space Science Institute (ISSI) through the ISSI International Team “Characterization of cometary activity of 67P/Churyumov-Gerasimenko comet”.

M.K. and T.M. acknowledge funding by ESA project "Primitiveness of cometary dust collected by MIDAS on-board Rosetta" (Contract No. 4000129476).

How to cite: Longobardo, A., Kim, M., Pestoni, B., Cottin, H., Guttler, C., Ivanovski, S., Mannel, T., Merouane, S., Rinaldi, G., Rubin, M., Tubiana, C., Zakharov, V., Deshapriya, P., Dirri, F., Ciarniello, M., Della Corte, V., Fulle, M., Palomba, E., and Rotundi, A.: Characterization of 67P/Churyumov-Gerasimenko cometary activity, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-459, https://doi.org/10.5194/epsc2022-459, 2022.

Comets, thought to be amongst the most primordial of Solar System objects, are distinguished by their activity, i.e. the insolation driven ejection of gas and dust from their surfaces. The exact mechanisms of the outgassing and dust ejection remain an important open question in planetary science, relating as it does to the structure, composition, and thermophysical properties of the surface material. Various thermophysical models (see e.g. [1,2,3]) have been proposed to explain the activity seen by Rosetta at 67P/Churyumov-Gerasimenko, with these often compared to the total outgassing rate. Another directly observable effect of the activity, however, is the resultant non-gravitational force and torque on the cometary nucleus, which can alter its trajectory and rotation state. Understanding the effect of non-gravitational forces on the dynamics of a particular comet therefore gives us a powerful additional tool to investigate its activity and surface properties.

Here we present the latest work in an ongoing project, testing various activity distributions in an effort to fit the combined Rosetta outgassing, trajectory, and rotation data. We test a number of different activity distributions over the surface of the comet by varying the Effective Active Fraction (EAF) of facets on a shape model, relative to a pure water-ice emission. We investigate different spatial patterns in EAF, and attempt to correlate them to physical features on the cometary surface. In addition to the changes in rotation period examined in [4], we also compute changes in the rotation axis, using a method based on [5] in order to compare with the observations. This provides an additional constraint on the spatial distribution of activity. Trajectory information, in the form of Earth-to-comet range, is also compared with a recent re-analysis of Rosetta radio-tracking data [6].

We are able to achieve a reasonable fit to the combined Rosetta data by parameterising EAF in terms of the different geological unit types on 67P (Fig. 1). This will have important implications for understanding how activity works on the different types of surface observed on cometary nuclei, including ‘rough’, ‘smooth’, ‘dusty’ and ‘rocky’ surface morphologies. The objective here is to constrain the shape of the activity curve on these various surfaces that a more detailed thermal model must produce in order to fit the data. We are in the process of implementing these more advanced thermal models [1,3] in our code, and will present results of an analysis of the non-gravitational forces and torques generated by [1].

Fig. 1. Peak Effective Active Fraction over the surface of 67P for a model fit to geological unit types.

References

• How comets work. Fulle, M. Blum, J., Rotundi, A., 2019. ApJ Letters, 879:L8 (3pp).
• Near-perihelion activity of comet 67P/Churyumov–Gerasimenko. A first attempt of non-static analysis. Yu. Skorov, H. U. Keller, S. Mottola and P. Hartogh. Monthly Notices of the Royal Astronomical Society, Volume 494, Issue 3, May 2020, Pages 3310–3316
• On the activity of comets: understanding the gas and dust emission from comet 67/Churyumov-Gerasimenko’s south-pole region during perihelion. B. Gundlach, M. Fulle, J. Blum. Monthly Notices of the Royal Astronomical Society, Volume 493, Issue 3, April 2020, Pages 3690–3715
• Constraining models of activity on comet 67P/Churyumov-Gerasimenko with Rosetta trajectory, rotation, and water production measurements. N. Attree, L. Jorda, O. Groussin, S. Mottola, N. Thomas, Y. Brouet, E. Kührt. Astronomy & Astrophysics 630, A18
• Kramer, T., Laeuter, M., Hviid, S., et al. 2019. A&A, Volume 630, id.A3, 11 pp.
• Lasagni Manghi R., Zannoni M., Tortora P., Kueppers M., O'Rourke L., Martin P., Mottola S., et al., 2020, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19173

How to cite: Attree, N., Argawal, J., Jorda, L., Groussin, O., Marschall, R., Lasagni Manghi, R., Tortora, P., and Zannoni, M.: Constraints on comet thermal models from Rosetta at 67P/Churyumov-Gerasimenko, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-5, https://doi.org/10.5194/epsc2022-5, 2022.

Remote sensing data of comets 9P/Tempel 1 and 67P/Churyumov-Gerasimenko (67P hereafter) indicate the occurrence of water-ice-rich spots on the surface of cometary nuclei [1-5]. These spots are up to tens of metres in size and appear brighter and bluer than the average surface at visible wavelengths.

In addition, the extensive observation campaign performed by the Visible and InfraRed Thermal Imaging Spectrometer (VIRTIS, [6]) and the Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS, [7]) during the Rosetta escort phase at 67P revealed a seasonal cycle of the nucleus colour. This is characterised by blueing of the surface while approaching perihelion followed by progressive reddening and restoral of the original colour along the outbound orbit. The temporal evolution of the colour has been interpreted in previous studies as the result of increasing exposure of water ice at smaller heliocentric distances [8, 9], however, an explanation of such seasonal cycle in the context of a quantitative cometary activity model was not yet been provided.

Recently, in [10] we showed that the seasonal colour cycle observed on comet 67P is determined by the occurrence of the above-mentioned water-ice-rich spots (referred to as Blue Patches – BPs –, given their colour). This can be explained in the context of activity models [11, 12] of pebble-made cometary nuclei [13], i.e. in terms of nucleus surface erosion induced by H₂O and CO₂ ices sublimation, driving the cometary activity.

According to the scenario proposed in [10] (Fig. 1), the presence of the BPs is due to the exposure of subsurface sub-metre-sized Water-ice-Enriched Blocks (WEBs) thanks to surface erosion triggered by CO₂ sublimation ejecting decimetre-sized chunks [12]. The WEBs are composed of ice-rich pebbles (dust-to-ice mass ratio δ=2, [14]), embedded in a matrix of drier pebbles (δ>>5) forming most of the nucleus. Once exposed to illumination as BPs, the WEBs are eroded by water-ice sublimation ejecting sub-cm dust [11]. By means of dedicated spectral and thermophysical modelling, we match the nucleus colour temporal evolution measured by the VIRTIS Mapping channel in the 0.55-0.8 µm spectral range. In doing this, we take into account the competing effects of CO₂- and H₂O-driven erosion that expose and remove the BPs, respectively, and are seasonally modulated by the insolation conditions, primarily depending on the heliocentric distance.

The new nucleus model proposed in [10], implying an uneven distribution of water ice in cometary nuclei, reconciles the compositional dishomogeneities observed on comets (the BPs) at macroscopic (up to tens of metres) scale, with a structurally homogeneous pebble-made nucleus at small (centimetre) scale, and with the processes determining the cometary activity at microscopic (sub-pebble) scales.

Figure 1. 67P surface gets bluer approaching perihelion as a consequence of the progressive exposure to sunlight of subsurface WEBs (from Figure 4 in Ciarniello et al., 2022, Nature Astronomy, https://doi.org/10.1038/s41550-022-01625-y). The comet nucleus is made of two types of pebbles, both including refractories and CO₂ ice, with different water ice content: pebbles with high content of H₂O ice form the WEBs, while H₂O-ice-poor pebbles represent the rest of the nucleus. CO₂ ice is stable beneath the CO₂ sublimation front at depths >0.1 m [12]. Approaching perihelion, the CO₂ ice sublimation rate increases, eroding the surface by chunk ejection and exposing the WEBs. Once exposed, WEBs lose CO₂ and are observable as BPs. Water-ice sublimation erodes the BPs ejecting sub-cm dust from their surface and preventing the formation of a dry crust [11]. The BPs survive until their water-ice fraction is sublimated, producing the observed surface blueing. Please refer to ref. [10] for complete details.

References

[1] Sunshine, J. M. et al. (2006) Science 311, 1453–1455.

[2] Filacchione, G. et al. (2016) Nature 529, 368–372.

[3] Raponi, A. et al. (2016) Mon. Not. R. Astron. Soc. 462, S476-S490.

[4] Barucci, M. A. et al. (2016) Astron. Astrophys. 595, A102.

[5] Oklay, N. et al. (2017) Mon. Not. R. Astron. Soc. 469, S582–S597.

[6] Coradini, A. et al. (2007) Space Sci. Rev. 128, 529–559.

[7] Keller, H. U. et al. (2007) Space Sci. Rev. 128, 433–506.

[8] Fornasier, S. et al. (2016) Science 354, 1566–1570.

[9] Filacchione, G. et al. (2020) Nature 578, 49-52.

[10] Ciarniello, M. et al. (2022) Nat. Astron. doi:10.1038/s41550-022-01625-y.

[11] Fulle, M. et al. (2020) Mon. Not. R. Astron. Soc. 493, 4039–4044.

[12] Gundlach, B. et al (2020). Mon. Not. R. Astron. Soc. 493, 3690–3715.

[13] Blum, J. et al. (2017) Mon. Not. R. Astron. Soc. 469, S755–S77.

[14] O’Rourke, L. et al. (2020) Nature 586, 697–701. 

Acknowledgements

We thank the Italian Space Agency (ASI, Italy; ASI-INAF agreements I/032/05/0 and I/024/12/0), Centre National d’Etudes Spatiales (CNES, France), and Deutsches Zentrum für Luft-und Raumfahrt (DLR, Germany) for supporting this work. VIRTIS was built by a consortium from Italy, France and Germany, under the scientific responsibility of IAPS, Istituto di Astrofisica e Planetologia Spaziali of INAF, Rome, which also led the scientific operations. The VIRTIS instrument development for ESA has been funded and managed by ASI (Italy), with contributions from Observatoire de Meudon (France) financed by CNES and from DLR (Germany). The VIRTIS instrument industrial prime contractor was former Officine Galileo, now Leonardo Company, in Campi Bisenzio, Florence, Italy. Part of this research was supported by the ESA Express Procurement (EXPRO) RFP for IPL-PSS/JD/190.2016. D.K. acknowledges DFG-grant KA 3757/2-1. This work was supported by the International Space Science Institute (ISSI) through the ISSI International Team "Characterization of cometary activity of 67P/Churyumov-Gerasimenko comet". This research has made use of NASA’s Astrophysics Data System.

How to cite: Ciarniello, M., Fulle, M., Raponi, A., Filacchione, G., Capaccioni, F., Rotundi, A., Rinaldi, G., Formisano, M., Magni, G., Tosi, F., De Sanctis, M. C., Capria, M. T., Longobardo, A., Beck, P., Fornasier, S., Kappel, D., Mennella, V., Mottola, S., Rousseau, B., and Arnold, G.: Seasonal evolution unveils the internal structure of cometary nuclei, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-105, https://doi.org/10.5194/epsc2022-105, 2022.

Vincent et al. (2016) studied a 3-month period surrounding comet 67P’s perihelion passage in August 2015. They detected and characterized 34 different dust outbursts with the Rosetta cameras. The sudden and brief release of dust of such transient events is characterized by a short lifetime. In their study, Vincent et al. (2016) estimated the source location of the observed outbursts. They were almost entirely on the Southern hemisphere and mostly located close to morphological boundaries of 67P. Thus, a link between morphology and the outbursts is assumed. In addition, these authors also approximated the local time since sunrise on the surface for each outburst event. Their result suggests that outbursts either appeared when the local surface is at its maximum daily temperature and subsurface volatiles produce an outburst, or when the Sun just began to shine onto the surface, thus inducing large temperature gradients and thermal cracking of the surface. In addition, Vincent et al. (2016) proposed that collapsing cliffs are the third mechanism triggering such events. However, the in-situ composition of the dust or gas released by the outbursts has not been studied yet, even though this might largely improve the knowledge about the underlying mechanisms generating such events.

In this work, knowing the source locations of the outbursts observed in Vincent et al. (2016), the gas composition in the coma after such events is studied by analysing ROSINA/DFMS mass spectrometry data and possible release mechanisms are discussed. A correlation in terms of angular separation of the sub-spacecraft latitude and longitude and the source location of the dust outburst is needed, as the gas speed is much faster than the observed dust outburst. Furthermore, Rosetta was mostly not directly above the source region during the actual camera observations. Only later or before, as the comet rotated, did Rosetta overfly the source location. Due to this time difference between the observation and the measurement of these dust events and thus the spread of the ejected gas, a distinct field of view needs to be defined in order decide whether the measured gas originated from the outburst source location or not. Consequently, it is possible that several outburst locations overlap with the same peaks in the gas ratios, making it difficult to differentiate a detection. In addition, as the outbursts were very short-lived appearances and thus mostly only detected in one image, the flow direction could not be determined making it impossible to partly decrease the field of view. Thus, a careful evaluation of each peak and its measurement configuration is necessary.

Figure 1 shows gas abundance ratios for CO₂, CO, CH₄, C₂H₆, CH₃OH, and C₃H₈ compared to H₂O for the outburst from 2015-07-26 20:22:42. For all depicted ratios, several peaks were measured at the time Rosetta flew over the outburst source location. This indicates that a larger amount of CO₂, CO, and different organic species compared to H₂O has been released by the outburst. It is possible that pockets of these species were buried just below the comet’s surface. Our findings show, that some features are already seen before the observed outburst itself, indicating a possible leakage of such gases creating such an event. Still, it is yet unknown whether these gases were responsible for the outbursts to appear or whether they were just released by the outburst as a by-product.

References:

Vincent, J.-B. et al., 2016, MNRAS, 462, S184–S194, https://doi.org/10.1093/mnras/stw2409

How to cite: Müller, D., Altwegg, K., Berthelier, J.-J., Combi, M., De Keyser, J., Fuselier, S., Pestoni, B., Rubin, M., and Wampfler, S.: Rosetta/ROSINA DFMS view of the summer fireworks on comet 67P, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-517, https://doi.org/10.5194/epsc2022-517, 2022.

Comets are the primitive building blocks of the Solar System. In order to understand the extent of the pristine nature of comets, we must understand the mechanisms that affect their surfaces and comae – their activity.

Activity can be tracked in a variety of ways, such as observing dust production in the coma and tail. We can study the activity in a quantitative way through photometry of the reflected sunlight, as flux is proportional to the reflecting area of the dust lifted off the comet by its activity. Activity varies from comet to comet so we must try to distinguish whether these differences in activity are because of ageing or reflect primordial differences. Ageing refers to effects that have chemically or physically altered the nucleus since its formation and may cause a change in the activity. The most obvious of which is the production of comae and tails, caused by escaping gas and dust lifted off the surface of the comet. Other signs of activity include outbursts, where material is suddenly ejected into the coma, causing an immediate and rapid brightening in telescopic observation.

All processes that physically and chemically alter a cometary nucleus can be regarded as ageing. The ageing processes are too slow and irregular to become detectable during a single observation. When comets are observed over a number of Solar System returns some changes can be detected (Meech & Svoren 2004). As such, that evolution of comets is best studied on a statistical basis.

Distinguishing the effects of ageing from primordial differences is important since the wide range of formation scenarios should imply significantly different observational qualities. Once the differences are established, it will allow us to use the comets as time capsules of the chemical and physical conditions in the early Solar System.

67P/Churyumov-Gerasimenko is a Jupiter-family comet that was the target of the Rosetta mission, the first mission to successfully orbit and land a probe on a comet. This mission was accompanied by a large ground-based observing campaign, the photometry from the campaign had been calibrated approximately by Snodgrass et al. (2017) but we present a more rigorous and accurate calibration.

We have developed a pipeline to calibrate and measure photometry of comet 67P during its 2016 perihelion passage, making use of all visible wavelength imaging collected across a wide range of facilities. The pipeline calibrates the brightness to a common photometric system (Pan-STARRS 1) using background stars in the field via the calviacat program (Kelley & Lister 2019).

The pipeline has been successfully applied to our entire data set of 67P imaging. The compiled light curve of the r-band observations are presented in Figure 1. The results follow predictions based on observations in previous orbits (Snodgrass et al. 2013) and show no obvious deviations, indicating that 67P doesn’t show significant changes due to ageing from orbit-to-orbit.

We will present results of a search for small-scale variation in activity that could be related to outbursts measured in situ by the spacecraft (Vincent et al. 2016). From manual inspection of the light curve we have identified one significant outburst, shown in Figure 2. This corresponds to an outburst seen in the comet coma morphology on the morning of 22 August 2015 by Boehnhardt et al. (2016). The date and time of this event corresponds to an outburst seen by the NavCam instrument onboard Rosetta (Vincent et al. 2016). However morphological differences and descrepancies between the estimates of the origin location make it difficult to draw a definitive connection between these two events. But it also unlikely that these outubursts are completely unconnected to this larger morphological change, perhaps these small outbursts were contributing to some unseen larger activity event.

We have placed constraints on these small-scale outbursts and their detectability from Earth-based observations and we constrain how well global activity measures relate to local changes on the comet nucleus. The lessons learned from Rosetta can be applied to the wider comet population, many of which will never be visited directly and only ever observed from the ground.

Figure 1: The r-band light curve of 67P/Churyumov-Gerasimenko measured within a 10,000 km aperture.

Figure 2: Light curve of signs of an outburst with the underlying trend removed. A sudden increase in brightness with a fall off typical of outburst is seen on and after the night of 22 August 2015, marked by the dot-dashed line. This corresponds to a morphological change in the coma seen by Boehnhart et al. (2016).

References
Boehnhardt H. et al., 2016, MNRAS, 462, S376
Kelley M., Lister T., 2019, mkelley/calviacat, doi:10.5281/zenodo.2635840
Meech K. J., Svoren J., 2004, in Comets II. Univ. of Arizona, Tuscon, pp 317–335
Snodgrass, C. et al., 2013, A&A, 557, A33
Snodgrass, C. et al., 2017, Phil. Trans. R. Soc. A, 375, 2016024
Vincent, J.-B. et al., 2016, MNRAS, 462, S184

How to cite: Gardener, D. and Snodgrass, C.: Searching for Outbursts in the Ground-Based Photometry of 67P/Churyumov-Gerasimenko, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-591, https://doi.org/10.5194/epsc2022-591, 2022.

Context

Circular depressions and alcoves were observed on the surface of some JFCs visited by spacecrafts: 81P/Wild 2 (Brownlee et al., 2004), 9P/Tempel 1 (Belton et al., 2013), 103P/Hartley 2 (Syal et al., 2013), and 67P/Churyumov- Gerasimenko (Vincent et al., 2015). These features are characterized by different shapes and sizes ranging from few tens to few hundreds of meters (Ip et al., 2016). Several studies investigated the thermal processing in relation to their formation and evolution (Guilbert-Lepoutre et al., 2016), and found that recent thermal activity in the inner solar system orbits is not sufficient to carve them. Ip et al. (2016) found that the size frequency distribution of the depressions on 67P, 81P and 9P has the same power law distribution, implying that they might have the same origin and formation mechanism. Dynamical simulations show that the thermal history of 81P and 9P is likely shorter than 67P’s and 103P’s, suggesting a younger surface. In this work, we investigate the thermally-induced evolution of depressions at the surface of 81P, 9P, 103P, and 67P under each of their current illumination conditions.

Methods

For these four nuclei, we select more than 10 surface features (i.e. depressions or alcoves). From their shape models, we select multiple facets on different sides of each feature (plateaux, bottom and walls) and consider the complete thermal environment for each facet, including self-heating and shadowing, either by neighboring facets or due to the complex global morphology of the nucleus. We compute the energy input for each facet during a full recent orbit, with a time step of ∼ 8 min. The total energy received at the surface is used as an input of a 1D thermal evolution model, which accounts for heat diffusion, phase transitions (sublimation of various ices and crystallization of amorphous water ice), gas diffusion, erosion, and dust mantling (Lasue et al., 2008). The thermal behaviour of each surface feature is investigated in detail.

Results

• We find that self-heating can be important in deep pits and steep cliffs of 67P and 81P (~65% and ~30% of the total energy input, respectively). In comparison, it is very low for 9P and 103P’s (<10%), where surface features are shallower.
  • Plateaux tend to erode more than the shadowed bottoms of sharp features, found on 67P and 81P: i.e. circular depressions become shallower with time. On 9P and 103P, erosion is more uniform since depressions are already shallower (as in the southern hemisphere of 67P). Overall, sharp depressions are likely erased by cometary activity.
  • Erosion sustained after the multiple perihelion passages is not able to carve depressions with the observed size and shape. It is therefore very unlikely that current illumination conditions were able to carve them.
  • We have, however, performed our simulations with a uniform set of thermo-physical parameters for all facets. Therefore, we cannot exclude that local or regional heterogeneities may yield different erosion rates.
  • A comparison between simulation outcomes for all nuclei allows to consider 103P as having the most altered surface. 9P could be an intermediate state. 81P would thus represent the least altered, or best preserved surface of these nuclei. Finally, 67P display a variety of surface ages, with areas as preserved as 81P, and a southern hemisphere as altered as 9P.

Acknowledgements

This study is part of a project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 802699). We gratefully acknowledge support from the PSMN (Pôle Scientifique de Modélisation Numérique) of the ENS de Lyon for the computing resources. We thank the European Space Research and Technology Centre (ESAC) and the European Space Astronomy Centre faculty council for supporting this research.

References

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Guilbert-Lepoutre, A., Rosenberg, E. D., Prialnik, D., & Besse, S. 2016, Monthly Notices of the Royal Astronomical Society, 462, S146
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How to cite: Benseguane, S., Guilbert-Lepoutre, A., Lasue, J., Besse, S., Beth, A., Grieger, B., and Teresa Capria, M.: Evolution of circular depressions at the surface of JFCs, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-256, https://doi.org/10.5194/epsc2022-256, 2022.

The phase curve of a small Solar System object shows the change in the object’s reflectance at different Sun-object-observer (phase) angles, and the shape of the phase curve is determined by the physical properties of the object’s surface. Analysing phase curves of small Solar System objects such as Kuiper belt objects (KBOs), Centaurs, and inert Jupiter-family comets (JFCs) can also probe the composition and regolith structure of their surfaces, and by comparing these across populations of objects, can reveal possible evolutionary connections between them.

The phase curve of an object can be significantly altered from its nominal shape if the object has undergone epochs of cometary activity during the time across which observations were taken. Furthermore, Centaur activity takes the form of outgassing in between long periods of quiescence, differing significantly from the activity exhibited by JFCs, which is more continuous and strongly coupled to heliocentric distance. As a result, Centaur activity may be difficult to identify from their phase curves if there are large time-intervals between observations. However, if observations are taken at sufficiently high cadence to isolate these outbursts, phase curves can be used to detect and analyse cometary activity out to distances where any coma may not be visible to Earth-based observations. This technique can help shed light on the mechanism responsible for the activity exhibited by Centaurs, which is presently not fully understood, and which is also an important step in understanding cometary evolution in the Solar System.

Obtaining such high cadence observations over multiple apparitions for phase curve analysis is difficult to achieve due to limited availability of telescope observation time, the large baseline of observations required, and the challenges of ground-based observing (poor weather and the limited observability of targets throughout the year). To circumvent these difficulties, many previous studies of phase curves augment their datasets by collating photometry obtained from different sources (Alvarez-Candal et al., 2016; Ayala-Loera et al., 2018; Alvarez-Candal et al., 2019). These additional data are often obtained with heterogeneous methods of image processing and data analysis, which might introduce systematic errors in the resulting phase curve. The Asteroid Terrestrial-impact Last Alert System (ATLAS) survey (Tonry et al., 2018a,b) has accumulated serendipitous observations of several bright KBOs, Centaurs, and JFCs, having observed the visible sky over a 2-day cadence, to a limiting magnitude of ~19.5 in two wide-band filters since it first began observations in 2015. ATLAS offers an opportunity to study the phase curves of these objects populated with large datasets and thus use them to search for epochs of cometary activity.

Using data from the Haleakalā and Mauna Loa telescopes of the ATLAS 4-telescope survey, we analyse the phase curves of the bright KBOs, Centaurs, and JFCs visible to ATLAS with datasets large enough that we do not need to include additional data from potentially heterogeneous sources, thereby reducing potential systematic errors. Our sample of 18 bright KBOs, JFCs and Centaurs visible to ATLAS span semimajor axes of 5.7 au ≤ a ≤ 67.9 au, absolute magnitudes of −1.1 < H_V < 13.3. Each object has on average 181 (c-filter) and 463 (o-filter) data points, exceeding the values of previous studies (Rabinowitz et al., 2007; Schaefer et al., 2009; Alvarez-Candal et al., 2016; Ayala-Loera et al., 2018; Alvarez-Candal et al., 2019), and which sample most of the phase angle range observable from Earth.

Figure 1: From Dobson et al. (2021), ATLAS Phase Curves of (2060) Chiron in c-filter (upper plot) and o-filter (lower plot), with data from most recent apparition indicated as black triangles. Black lines represent linear best fits to data.

We present our findings on using ATLAS phase curves with their advantage of unprecedentedly large datasets to search for instances of cometary activity exhibited by our sample of KBOs, JFCs and Centaurs since 2015. Notably, we discover a recent brightening of the Centaur (2060) Chiron (Dobson et al. 2021), as seen in Figure 1, which despite the lack of detected coma, is indicative of either an outburst or enhanced activity.

Acknowledgements

We made use of the ATLAS Forced Photometry Server to obtain our Centaur and KBO photometry. https://fallingstar-data.com/forcedphot/

This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (AT- LAS) project. ATLAS is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen’s University Belfast, the Space Telescope Science Institute, the South African Astronomical Observatory (SAAO), and the Millennium Institute of Astrophysics (MAS), Chile.

References

Alvarez-Candal, A., Ayala-Loera, C., Gil-Hutton, R., et al. 2019, MNRAS, 488, 3035, doi: http://doi.org/10.1093/mnras/stz188010.1093/mnras/stz1880

Alvarez-Candal, A., Pinilla-Alonso, N., Ortiz, J. L., et al. 2016, A&A, 586, A155, doi: http://doi.org/10.1051/0004-6361/20152716110.1051/0004-6361/201527161

Ayala-Loera, C., Alvarez-Candal, A., Ortiz, J. L., et al. 2018, MNRAS, 481, 1848, doi: http://doi.org/10.1093/mnras/sty236310.1093/mnras/sty2363

Dobson, M. M., Schwamb, M. E., Fitzsimmons, A., et al. 2021,
Research Notes of the AAS, 5, 9, doi: http://doi.org/10.3847/2515-5172/ac26c9

Rabinowitz, D. L., Schaefer, B. E., & Tourtellotte, S. W. 2007, AJ, 133, 26, doi: http://doi.org/10.1086/50893110.1086/508931

Schaefer, B. E., Rabinowitz, D. L., & Tourtellotte, S. W. 2009, AJ, 137, 129, doi: http://doi.org/10.1088/0004-6256/137/1/12910.1088/0004-6256/137/1/129

Tonry, J. L., Denneau, L., Heinze, A. N., et al. 2018a, , 130, 064505, doi: http://doi.org/10.1088/1538-3873/aabadf10.1088/1538-3873/aabadf

Tonry, J. L., Denneau, L., Flewelling, H., et al. 2018b, ApJ, 867, 105, doi: http://doi.org/10.3847/1538-4357/aae38610.3847/1538-4357/aae386

How to cite: Dobson, M. M., Schwamb, M. E., Benecchi, S. D., Verbiscer, A. J., Fitzsimmons, A., Shingles, L. J., Denneau, L., Heinze, A. N., Smith, K. W., Tonry, J. L., Weiland, H., and Young, D. R.: Using Phase Curves from ATLAS to Search for Cometary Activity in the Solar System, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-878, https://doi.org/10.5194/epsc2022-878, 2022.

Context

Jupiter-family Comets (JFCs) is a cometary population with a rich evolutionary history. Originating from the Kuiper Belt and the scattered disk, they evolve in the giant-planet region, where they spent a considerable amount of time as Centaurs, before reaching Jupiter-crossing orbits through a series of close encounters with the giant planets [1]. The recent observations of long-distant cometary activity (e.g. [2]), alongside with the existence of active Centaurs [3] suggest the possibility of thermal processing during their journey towards their current positions in the inner solar system. In this study we seek to investigate this potential thermal processing from the moment a comet leaves its reservoir and throughout its evolution in the giant-planet region, until its ejection from the solar system.

Methods

We use a sample of 276 simulated JFCs successfully representing the orbital distribution of JFCs, taken from a N-body simulation tracking the orbital evolution of the giant planets and a large number of small bodies of the outer planetesimal disk [4]. We apply a 1D thermal evolution model [5] on every simulated JFC in order to resolve the heat diffusion equation and obtain the temperature distribution in their interiors. Simplifications are adopted in order to overcome the complexity imposed by the different timescales of the thermal and dynamical processes involved. Special consideration is given to the thermal conductivity, key parameter of the thermal evolution model, to assess its influence in the simulation's results.

Results

The stochastic nature of the trajectories towards the inner solar system results in a pattern of long-lasting periods of heating, randomly spread out over the simulated JFCs lifetimes. As a consequence significant subsurface layers are heated, providing the conditions for substantial alterations to take place. Free condensed hypervolatile species are mostly concerned, as temperatures allowing their sublimation can be found down to the innermost parts of the nucleus in the majority of the objects in our sample. Layers extending several tenths of meters below the surface are also liable to lose primordial condensed moderately-volatile material, while the front of amorphous water-ice is expected to withdraw by a few meters as well.

Perspectives

This study suggests that for any typically observed JFCs, activity is very likely triggered from already processed subsurface layers, indicating the necessity to account for the entire evolutionary history in order to interpret current observations in a broader context.

Acknowledgements

This study is part of a project that has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (Grant agreement No. 802699). We gratefully acknowledge support from the PSMN (Pôle Scientifique de Modélisation Numérique) of the ENS de Lyon for the computing resources.

Example of the temperature distribution for the first 200m below the surface for a simulated JFC, after leaving the Kuiper Belt (panel (a): orbital evolution given by an averaged semimajor axis), for three different values of the thermal conductivity (panels (b) to (d): 5.4 10^-3, 5.4 10^-4 and 5.410^-5 Wm^-1K^-1) respectively.

How to cite: Gkotsinas, A., Guilbert-Lepoutre, A., Raymond, S., and Nesvorny, D.: On the thermal processing of Jupiter-family Comets, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-201, https://doi.org/10.5194/epsc2022-201, 2022.

A stellar occultation occurs when an object (an asteroid, trans-Neptunian object, Centaur) passes in front of a distant star, blocking its light momentarily. The occultation technique allows deriving accurate positions, sizes, and shapes of small solar system objects. The accuracy of the predicted path of the occultation shadow has improved significantly in the last decade, increasing the number of viable targets for study via stellar occultations. The improvement is due mainly to the availability of an accurate astrometric catalog provided by the Gaia mission. In practice, the primary source of uncertainty in the predictions is the uncertainty in the occulting object ephemerides.

The analysis of stellar occultation measurements can be challenging in cases where there is photometry with a low signal-to-noise ratio, a short duration of the event, low temporal or spatial sampling, or a combination of those. Also, we need to account for cases with multiple occulting objects, and multiple occulted stars or combined detection of the same objects at different epochs. In these cases, we can have model parameters with significantly correlated uncertainties and where it is not trivial to discriminate between different models, requiring a rigorous quantitative approach. Last but not less, we need to account for the influence of the model a priori assumptions on the derived parameter values and uncertainties.

Bayesian statistics allow for analysis of these challenging cases, providing posterior probabilities for the object(s) size, shape, and orientation parameters and quantitative comparison of different possible models.

I have adopted a Bayesian approach for analyzing occultations measurements, including multi-epoch detections, single and multi-station detections, single and double objects, and occulting single and double stars.

I will present the application of the approach to the analysis of stellar occultation by Trans-Neptunian objects and Centaurs, exemplified by interesting cases from different projects and collaborations, both published or in the process of publication, including the ringed Centaur (10199) Chariklo, the extreme TNO (541132) Leleākūhonua, the small Centaurs 2014 YY49 and (591376) 2013 NL24, the binary TNO (523764) 2014 WC510, and the retrograde Centaur (342842) 2008 YB3 [1, 2, 3, 4].

References:

1. Strauss, Leiva, Buie et al. 2021. PSJ, 2, 1, 22.

2. Leiva, Buie, Keller et al. 2020. PSJ, 1, 2.

3. Buie, Leiva, Keller et al. 2020. AJ 159, 5.

4. Leiva, Sicardy, Camargo et al. 2017. AJ 154, 4.

How to cite: Leiva, R.: On the Bayesian analysis of stellar occultation by small solar system bodies, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-669, https://doi.org/10.5194/epsc2022-669, 2022.

Introduction

GAIA mission astrometric data for stars in Solar System neighbourhood allow us to find a probable past and future stellar flybys at distance lower than 3000 au (for example HD 7977 flyby 2.5 million years ago). However the distance and geometry of such flybys have large relative uncertainties and it is possible that flybys at a distance of several hundreds of astronomical units have happened in recent past. We performed the numerical analysis of very close stellar flyby investigating different flyby geometries and distances. In the analysis we simulated the dynamics of planets and Kuiper Belt minor bodies during the passage of a Sun-like star using the Rebound n-body simulator software. Using the past flyby of HD 7977 star as a reference we assumed the star with mass close to the mass of the Sun and relative velocity of tens of km/s.

Before analysing the effect of star passage on minor bodies we decided to check the impact on the orbits of giant planets. We discovered that flybys at distance greater than 300 au change the eccentricity of giant planets by less than 0.01 and the semimajor axis by less than 0.1 au. This allows us to ensure that such close flyby can have small effect on planets and not disturb the stability of Solar System and therefore they could happened in the past. The probability of significant disturbance of planetary orbits grows when the minimal star-Sun distance is smaller, but even for extremely close distances (about 100 au) in most cases it is possible to find specific geometry of flyby where planetary orbits are not heavily changed.

Kuiper Belt and scattered disc simulation

In order to investigate the effect of stellar flyby on Kuiper Belt objects, we simulated the synthetic, randomly generated population of minor bodies with semimajor axis greater than 30 au. We checked the statistical properties properties of orbital elements of this population after the close flyby. The results shows that flyby at 3000 au will not create significant change in the orbital parameters of this objects. However the closer passages do affect the population and may create various statistical effects on the population.

Last years the analysis of the orbital parameter of most distant Solar System objects shows the significant perihelion direction clustering. This leads to the formulation of the Planet Nine hypothesis by Batygin et al. In this model, the orbital characteristic of distant objects is explained by the existence of an undiscovered massive planet that orbits the Sun at a distance of about 1000 au. Our simulations also included scattered disc objects including distant bodies with the semimajor axis equal to several hundreds of astronomical units. We want to show if the very close star passage can be used as an alternative explanation of the orbital properties of distant bodies. We also checked what would be the possible effect of a star flyby on hypothetical Planet’s Nine orbit.

Conclusion

Our simulation shows that there is possibility of a close stellar flyby which do not disturb the planetary system affecting its stability, but such flyby can affect the minor body population, especially the distant part of the Kuiper Belt. This possibility should be taken into account in modelling the outer Solar System minor body population.

How to cite: Langner, K. and Bartczak, P.: The effect of close stellar flybys on the distant minor body population., Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-401, https://doi.org/10.5194/epsc2022-401, 2022.

In the past, it has been controversially discussed how pristine or primordial the comets of the Solar Systems are. Here we present an overview of our understanding of their formation and evolution from dust and ice grains in the solar nebula towards the small bodies we observe today. The first phase is given by the agglomeration of dust and ice grains in the protoplanetary disk until mm- to cm-sized aggregates (“pebbles”) form, which cannot grow further due to the bouncing barrier. The formation of planetesimals is then caused by the gentle gravitational collapse of a concentrated pebble cloud. The formed planetesimals undergo different evolutionary phases, in which they can be altered by radiogenic heating and by mutual collisions. Radiogenic heating can lead to differentiated planetesimals, in which the volatiles are redistributed inside the bodies. Differentiation can be avoided if the planetesimals are relatively small or were formed late. Concerning collisional evolution, we define three types of impacts: sub-catastrophic, catastrophic, and super-catastrophic collisions, which differ in the degree of thermal and mechanical alteration of the bodies. After these phases of our model, the evolution ends with five types of small bodies, and we further discuss which of them can be regarded as comets, using their observed physical properties. Comparing these results with empirical data from comets, in particular from the Rosetta mission to comet 67P/Churyumov-Gerasimenko, conclusions about comet formation and evolution are drawn and open questions are highlighted. This work shall also shed light on possible observation methods that could be used to further constrain comet formation.

How to cite: Bischoff, D., Gundlach, B., and Blum, J.: The formation and evolution of planetesimals towards comets – an overview, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-18, https://doi.org/10.5194/epsc2022-18, 2022.

The initial process of planetesimal formation is the coagulation of micrometer-sized solid particles. In the inner regions of a protoplanetary disk, silicate dust is the dominant material. Further out beyond the corresponding snow lines, various other volatile compounds condense and serve as additional building material for planetesimals. The most frequent compounds are H₂O, CO₂ and CO.

Since the coagulation behavior largely depends on the properties of the building material, an understanding of these properties is essential to comprehend the first steps in planetesimal formation. To provide a systematic analysis on this, we conducted experiments on the collision behavior and the mechanical properties of CO₂-ice agglomerates, consisting of micrometer-sized particles.

Collisions of agglomerates with sizes of 10 µm to 150 µm are analyzed to investigate the collision behavior. The coagulation is studied at temperatures around 100 K and a pressure of 1 mbar with impact velocities of up to 3.4 m/s. The collisional outcome is analyzed regarding the events of sticking, bouncing or fragmentation. Below impact velocities of 0.1 m/s sticking is observed. Above 0.1 m/s the particles bounce inelastically, with a maximum coefficient of restitution of 0.5 only. For velocities higher than 1 m/s fragmentation of the agglomerates sets in. The three velocity ranges are shown in fig. 1. The experiments indicate that the collision behavior of CO₂-ice agglomerates is similar to that of silicate agglomerates with a comparable grain size distribution [Fritscher M., Teiser J., 2021, ApJ, 923, 134].

Fig. 1: Coefficient of restitution ϵ for sticking (lighter blue dots) and bouncing events (darker blue dots) and fragmentation strength μ (red triangles) depending on the impact velocity [Fritscher M., Teiser J., 2021, ApJ, 923, 134].

To examine the mechanical properties of CO₂ ice, the well-established method of the Brazilian test is used. For varying volume fillings between 0.35 and 0.54, the splitting tensile strength is determined. As can be seen in fig. 2 it follows a power law, with values between 2·10⁴ Pa and 10⁵ Pa. The effective surface energy is derived from the measured splitting tensile strength as 0.060±0.022 J/m². The surface energy depending on the volume filling is shown in fig. 3 [Fritscher M., Teiser J., 2022, MNRAS, 512, 3754].

Fig. 2: Tensile strength σ depending on the volume filling Φ [Fritscher M., Teiser J., 2022, MNRAS, 512, 3754].

Fig. 3: Surface energy γ depending on the volume filling Φ [Fritscher M., Teiser J., 2022, MNRAS, 512, 3754].

For silicates simulation methods and models exist, describing aggregate collisions and the evolution of dust in protoplanetary disks. The collision experiments show that these models can also be applied to collisions of CO₂-ice agglomerates, when scaled properly with the surface energy. Therefore, we conclude that the growth processes known for silicate dust also apply for CO₂ ice, including growth barriers as the bouncing barrier or the fragmentation barrier.

References

Fritscher, M. and Teiser, J. (2021). The Astrophysical Journal, Volume 923, Issue 2, id. 134, 9 pp. DOI: 10.3847/1538-4357/ac2df4

Fritscher, M. and Teiser, J. (2022). Monthly Notices of the Royal Astronomical Society, Volume 512, Issue 3, pp. 3754-3759. DOI: 10.1093/mnras/stac676

How to cite: Fritscher, M. and Teiser, J.: Particle growth beyond the CO2 snowline – dynamic and mechanical properties of CO2 ice, Europlanet Science Congress 2022, Granada, Spain, 18–23 Sep 2022, EPSC2022-231, https://doi.org/10.5194/epsc2022-231, 2022.