Comet 12P/Pons-Brooks is a great Halley-family comet with an orbital period of
71 years, that was first seen in 1385, and possibly earlier. It returned
to perihelion on 21 April 2024 at 0.78 au from the Sun (Fig.1)
Its peak outgassing rate exceeded Q_H2O=10³⁰ molec.s^-1, with a
total visual magnitude of 4 in April and the comet was the focus of a
worldwide observing campaign.
We report observations of the comet with IRAM-30m and NOEMA facilities
on 20 January, 17, 20 March, and 22-28 April 2024. A frequency survey at
3, 2 and 1 mm wavelengths, covering 8, 24 and 63 GHz respectively, was undertaken in April
under average weather conditions.
Several molecules and isotopologues were detected. We have derived expansion
velocity, gas temperature and production rates or upper limits on molecular
abundances. Around perihelion we measured an expansion velocity around 1.1 km/s
and a gas temperature of around 105 K.
Lines of HCN, HNC, HC₃N, CH₃CN, HNCO, NH₂CHO, CH₃OH, H₂CO, CO, HCO⁺, CS,
H₂S, OCS, SO, C³⁴S and possibly (CH₂OH)₂ have been detected (Fig.2) and the molecular
abundances will be presented. This is the most detailed chemical
inventory of a Halley-family comet obtained so far. The composition of 12P
will be compared to previously investigated long- and short-period
comets.

Figure 1: Comet 12P/Pons-Brooks on 6.83 March 2024 UT. Visible image obtained with a 40.7-cm telescope, Field of view is 40x40 arcmin. (c) N. Biver

Figure 2: Sample average spectra of lines observed with IRAM-30m in April 2024.
The vertical scale in main beam brightness temperature (in K) is preliminary.
Horizontal axis is Doppler velocity in the rest frame of the comet.

Acknowledgements:

This work is based on observations carried out under projects number W23AA001 and 066-23 with the IRAM NOEMA Interferometer and 30m telescopes.
IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004).

How to cite: Biver, N., Boissier, J., Bockelée-Morvan, D., Crovisier, J., Moreno, R., Cordiner, M., Lis, D. C., Roth, N., Bonev, B., Milam, S., Drozdovskaya, M., and Opitom, C.: Investigating the composition of  Halley-family comet 12P/Pons-Brooks with IRAM radio telescopes, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-371, https://doi.org/10.5194/epsc2024-371, 2024.

I–Introduction 

Comet 12P/Pons-Brooks is a Halley-type comet discovered in 1812. Returning every 71 years from just beyond the orbit of Neptune, outbursts were reported during each of its apparitions since. On its way to its most recent perihelion passage (21/04/2024) the comet exhibited large outbursts, such as on 20/07/2023 (magnitude ∼17 to∼12) or 14/11/2023 (magnitude ∼14 to∼9), with several smaller outbursts in between.

Outbursts can be linked to mechanical processes (e.g fragmentation), external phenomena (e.g collisions) or internal physico-chemical processes (e.g. crystallisation of ice)[1]. Regular outbursts on 12P might indicate that its structure or make-up are to blame. The 2024 return of the comet presented a perfect opportunity to study its composition and behaviour.

II–Methods 

         Long slit spectra of 12P were acquired with the Isaac Newton Telescope(INT) IDS on 23/08/2023, 17-18/11/2023, and with the Nordic Optical telescope(NOT) ALFOSC on 17/12/2023. They cover the spectral range 304-640nm for INT-IDS and 350-535nm for NOT-ALFOSC, probing emission regions of common radicals such as CN, C₂, C₃, etc. We calculated molecular production rates Q and upper limits of OH, NH, CN, C₂ and C₃ by comparing the integrated flux within a 10000km distance from the nucleus to a standard Haser model. We used a gas velocity of v=1km/s as well as commonly used scale-lengths and fluorescence factors. We also produced column density profiles of CN, C₂ and C₃ along the spectrograph slit (aligned with the parallactic angle). These can help searching for features, studying the release mechanisms of species by comparing them to models, etc.

III–Results 

Based on our observations (e.g. Fig. 1), the composition of 12P (Table 1) seems typical, although slightly carbon-depleted (average Q(C₂)/Q(CN)=0.913±0.053) and slightly low in OH compared to other radicals. Abundance ratios do not seem to vary significantly from November to December and seem in agreement with preliminary production rates from the TRAPPIST telescopes (e.g. [2]). Paired with these measurements, our observations from November show a decline of the 14/11/2023 outburst gas release within a few days.

         In November, we measure slightly asymmetrical profiles for C₂, C₃ and CN. In December, the asymmetry is even stronger (Fig. 2). This is consistent with multiple reports of a complex coma morphology (e.g [3]). A faint feature is visible in the CN profile on 17/11/2023, which could be a minor outburst amidst the large 14/11/2023 outburst. While C₂ and C₃ would be expected to have similar release mechanisms, the C₂ profiles look particularly “flat” while C₃ and CN look more “peaked”, perhaps indicating a separate origin.

         As illustrated by Fig. 3, the expected Haser model with empirical scale-lengths fails to reproduce the observed profiles. For all profiles, adjusting the model with variable scale-lengths and Q values returns parent and daughter scale-lengths that are close to equal. These parameters translate into profile shapes in log-scale that are more angular (flat then sharply decreasing) than expected with the Haser model and usual parameters. Such shapes can also be obtained by more complex Haser models such as three-generation or grain-halo models[4]. This could suggest the presence of extended sources in the coma, especially for C₂ which seems to behave unusually. With the Q values found by adjusting the Haser model parameters to the profiles, the comet does not seem carbon-depleted anymore. While the adjusted profiles still do not exactly match the observations (especially for C₂), this highlights the complexity of composition measurements and classification for “unusual” comets for which the standard model may not apply.

Figure 1 – Average INT-IDS optical spectrum of comet 12P on 17/11/2023, integrated within 10000km from the nucleus, showing detection of emission lines from several species.

 Table 1  –  Molecular production rates and abundance ratios calculated from INT-IDS (2” slit-width) and NOT-ALFOSC (1” slit-width) spectra of 12P (e.g. Fig 1) using a standard Haser model (v=1km/s) in a 20000km wide aperture.

Figure 2 – Column density profiles of CN, C₂, C₃ along the spectrograph slit on 17/11/2023 and 17/12/2023 (added y-offsets for C₂ and C₃). Solid black lines show the average binned data, dotted gray lines show these binned profiles reversed along the x-axis. A bump is visible 50000km away from the nucleus on 17/11/2023 which could be a minor outburst. Unlike CN and C₃, the C₂ profiles appear almost linear with the radial distance.

Figure 3 – Column density profiles of CN, C₂, C₃ along the spectrograph slit (one side only) on 17/11/2023, with expected Haser model profiles and best Haser model fits. The models use v=1km/s. Expected models use literature scale-lengths and Q values from Table 1 (vertical grey lines indicate our 10000km aperture).

Acknowledgements

         We acknowledge contributions from J.P.U. Fynbo and U.G. Jorgensen for the 12/2023 NOT data as well as A. Donaldson and R. Kokotanekova for the 08/2023 INT data.

References

[1] Hughes, D.W. (1990). Cometary outbursts - A review. QJRAS, vol. 31, pp. 69–94.

[2] Jehin, E. et al., (2023). TRAPPIST bright comets[…]. ATel, 16338.

[3] Knight, M.M. et al., (2024). Rotation period[…]. ATel, 16508.

[4] Combi, M.R., & Fink, U. (1997). A Critical Study[…]. AJ, 484(2), 879.

How to cite: Ferellec, L. and Opitom, C.: Coma composition and profiles of 12P/Pons-Brooks from long-slit spectroscopy, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-313, https://doi.org/10.5194/epsc2024-313, 2024.

We present pre-perihelion photometric and spectroscopic observations of comet 12P/Pons-Brooks (hereafter 12P) during its 2024 passage. 12P is a comet on a Halley-type orbit with a period of 71 years that showed during its recent approach several impressive outbursts[1], with an interesting double horn shaped dust coma which earned it the nickname of "devil comet". The comet, discovered in 1812, had already experienced outbursts during previous passages [2]. We observed the comet over 125 nights with the TRAPPIST-North telescope [3] from May 6, 2023 (rh = 4.62 au), to March 16, 2024 (rh = 1.02 au), when it was too close to the Sun to be observed. We collected images with broad-band Johnson–Cousins filters (BVRI) as well as narrow-band HB filters [4] (OH, CN, C₂, C₃ and NH for gas species and BC, GC and BC for the dust continuum) to compute the comet lightcurve in BVRI, the gas activity using the Haser model [5], and the dust activity proxy af(0)rho [6]. From the lightcurve and images we detect at least 6 major outbursts with an increase up to 4 magnitudes (see Fig. 1 and [1]) along with gas and dust increase; OH production rate reaching values as high as 10²⁹ molecules/s and af(0)rho as high as 10⁵ cm. Interestingly, most of the outbursts where observed at a heliocentric distance higher than 3 au, where supervolatiles such as CO₂ and CO probably drives cometary activity. It indicates that the outburst mechanism might be similar to other far away comets such as the centaur 29P/Schwassmann–Wachmann 1 that shows regular outbursts at an heliocentric distance of ~ 6 au [7]. The outbursts and their subsequent fall-off were observed with narrow-band filters allowing the study of the gas and dust ratios behavior during those events. The analysis of the images in the various filters shows the evolution of the peculiar 12P coma shape with the activity.

To complement the TRAPPIST photometric dataset, long-slit low resolution spectra were obtained at the Observatoire de Haute Provence with the MISTRAL instrument [8] (5.5’x1.9’’ slit, R∼700@6000 Å) on the night of March 23, 2024, when the comet was at a heliocentric distance of 0.94 au (Fig. 2). Spectra was extracted from the observed data and calibrated to analyse the emissions from the different molecular bands. While the usual emission bands from the neutral molecular species, C₂ , NH₂ , CN, are observed, additionally, a tentative detection of H₂O⁺ has also been made.

Fig. 1: 12P/Pons-Brooks magnitude in the R band from the TRAPPIST survey. Several outbursts with a 1 to 4 magnitude increase can be observed. The lightcurve covers observations from May 6, 2023 (rh = 4.62 au), to February 25, 2024 (rh = 1.27 au)

Fig. 2: 120s spectra of 12P taken with MISTRAL at Observatoire de Haute Provence with a 1,9’’ wide slit, dust subtracted and extracted on the photocenter. Different emission bands are visible, including tentative detections of H₂O⁺.

References

[1] ATel#16194, ATel#16202, ATel#16223, ATel#16229, ATel#16254, ATel#16270, ATel#16282, ATel#16315, ATel#16338, ATel#16343, ATel#16408, ATel#16498

[2] Gary W Kronk, Cometography: a catalog of comets. Vol. 4, 1933-1959, Cambridge University Press (2009)

[3] Jehin, E. et al. TRAPPIST: TRAnsiting Planets and PlanetesImals Small Telescope. The Messenger 145, (2011).

[4] Farnham, T. The HB Narrowband Comet Filters: Standard Stars and Calibrations. Icarus 147, 180–204 (2000).

[5] Haser, L. Distribution d’intensité dans la tête d’une comète. Bulletins de l'Académie Royale de Belgique 43 pp. 740-750 (1957)

[6] A'Hearn et al., Comet Bowell 1980b, The Astronomical Journal 89-4, 579-591 (1984)

[7] see the MISSION 29P campain: https://britastro.org/section_information_/comet-section-overview/mission-29p-2

[8] Schmitt, J. et al. Multi-purpose InSTRument for Astronomy at Low-resolution: MISTRAL@OHP. Preprint at http://arxiv.org/abs/2404.03705 (2024).

Acknowledgments

TRAPPIST is a project funded by the Belgian Fonds (National) de la Recherche Scientifique (F.R.S.-FNRS) under grant T.0120.21. This work is supported by the BIPASS program from the International Division of Department of Science and Technology (DST; Govt. of India) and the Belgian Federal Science Policy Office (BELSPO; Govt. of Belgium). M.V.D. acknowledges support from the French-speaking Community of Belgium through its FRIA grant

How to cite: Vander Donckt, M., Jehin, E., Krishnakumar, A., Adami, C., Hmiddouch, S., Ganesh, S., Benkhaldoun, Z., Delsanti, A., and Jabiri, A.: Pre-perihelion TRAPPIST monitoring of the outbursting Halley-type comet 12P/Pons-Brooks, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-951, https://doi.org/10.5194/epsc2024-951, 2024.

It is believed that small celestial bodies contain primordial material from the Solar System formation epoch. Long-period comets that due to their dynamical characteristics spend mostly of time far from the Sun consist of mater barely differentiated by the Solar radiation. Moreover, comets that coming into the inner part of the Solar System at the first time are the most prominent objects for study from this point of view. Comet C/2022 E3 (ZTF) is a hyperbolic comet was discovered on March 2, 2022, with the 48-inch Schmidt-type telescope of the Zwicky Transient Facility (ZTF), as an object of approximately 17.3^m at a heliocentric distance of r_h = 4.3 au (Bolin et al. 2022). C/2022 E3 (ZTF) reached a perihelion distance of 1.112 au on January 12, 2023. We present the results of observations obtained after the perihelion passage using broad- and narrowband photometrical, and long-slit spectral methods. Such complex analysis allows us to study more precisely the dust and gas components of the comet.

Observations. The observations of comet C/2022 E3 (ZTF) were carried out from January 23 to February 20, 2023, right after the perihelion passage when the heliocentric and geocentric distances of the comet changed from 1.127 to 1.276 au and from 0.402 to 0.684 au, respectively. It worth be noted that during our observation the comet made its closest approach to the Earth on January 31, 2023.

Photometrical observations were performed at 61-cm telescope of Skalnaté Pleso observatory (Slovakia). We used the CCD chip SBIG ST-10 Dual with 1092px×736 px after applying 2×2 binning. The pixel’s size was 13.6×13.6 μm corresponding to 1.07ʺ/px on the sky plane after binning. We used broadband B, V, R Johnson-Causins filter and narrowband cometray filters BC, C₂, RC.

We provided spectral observations of the comet on 40ʺ Zeiss telescope of Vainu Bappu Observatory (Kavalur, India) and 2.0-m Himalyan Chandra Telescope of the Indian Astronomical Observatory. The long-slit spectra were obtained using several grisms as a disperser. The slit size was 2ʺ ×11ʹ was placed on the nucleus position in the sky. The obtained spectra covered the wavelength range 4000–7800 Å.

Results. Photometry. We estimated the dust productivity using the Afρ parameter. It was about 2500 cm in red domain. The comet also demonstrated typical red colour, based on V-R and BC-RC calculated values. To reveal the low-contrast structures in the dust coma, we constructed an intensity map of comet C/2022 E3 (ZTF) using digital filters. Based on the distribution map of intensity, we derived the radial profiles of the surface brightness for observed structures to describe the dust brightness as a function of the distance from the optocenter. The profiles demonstrate slopes differed from the value -1, which corresponds to the case of a steady and isotropic emission of long-lived grains.

Spectroscopy. We analyzed cometary spectra in the wavelength region of 4000–7800 Å. Significant gas emission lines were detected in the spectra. The strongest features belong to molecules of C₂, C₃, and NH₂. Gas production ratios were calculated for all detected molecules using the Haser model [2]. Also, we estimated the gas contribution in wavelength regions corresponding to broadband filters used for photometric studies. To compare with photometrical results, we also computed a colour slope value based on the spectral data. The results from both methods are in good agreement.

Acknowledgments. The research is supported by the Government Office of the Slovak Republic within NextGenerationEU programme under project No. 09I03-03-V01-00001, the Slovak Academy of Sciences (grant Vega 2/0059/22), the Slovak Research and Development Agency under the Contract no. APVV-19-0072, the DST, Government of India, under the Women Scientist Scheme (PH) project reference number SR/WOS-A/PM-17/2019.

References

[1] Bolin, B. T., Masci, F. J., Ip, W.-H., et al. (2022), MPEC (USA: IAU), 2022-F13

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

How to cite: Shubina, O., Ivanova, O., Husárik, M., Safonova, M., Venkataramana, A., Selvakumar, G., and Narang, M.: Post-perihelion activity of comet C/2022 E3 (ZTF), Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-352, https://doi.org/10.5194/epsc2024-352, 2024.

The composition of comets provides key insights into the physical, chemical, and evolutionary processes that shaped our and other planetary systems [1]. Furthermore, it can reveal whether the material in our Solar System was primarily inherited from the proto-solar nebula or reprocessed during its formation [2,3].

Ground-based high-resolution infrared spectroscopy (∼2 to 5 μm) reveals a complex chemical heterogeneity in comets [4,5], which may be consistent with the numerous processes that may have occurred in our protoplanetary disc during their formation [2,3,6], as well as the dynamical models that predict their dispersion into current reservoirs after formation [7]. This makes it difficult to chemically categorize comets and link the observed differences to their specific formation site. Nevertheless, with improved global observing facilities and instrumentation, the amount of available data has increased, allowing for a more accurate statistical approach.

Here, we present the statistical analysis of molecular abundances of a few species in 35 comets as measured by infrared high-resolution spectroscopy [8]. Our research aims to: (i) explore for significant differences across dynamical families (e.g., Jupiter-family/short-period vs. Oort-Cloud/long-period comets) that could be linked to disk processes and/or comet material evolution after storage; (ii) search and possibly compensate for observational biases in the data; (iii) find potential taxonomical classes for comets, and (iv) compare  the molecular abundance ratios measured in comets with those retrieved in planet-forming systems. Our database also includes recent results relative to comets observed with CRIRES⁺ at VLT/ESO (among them C/2023 A1 (Leonard) [9] and C/2023 H2 (Lemmon) [10]), which will be displayed individually to demonstrate this instrument capabilities.

Among other findings, we will show the existence of significant biases correlated to the observing conditions for specific molecular species (e.g., the excess of H₂CO in comets observed within 1 au from the Sun), and how these biases may influence our understanding of the comet chemistry in the context of planet formation. We will compare the database’s averaged molecular abundances to those obtained by the ESA-Rosetta mission [11], revealing significant differences between 67P/Churyumov-Gerasimenko and other comets. Finally, we will illustrate how the overall results can be generalized to planet formation by comparing molecular abundance ratios (such as [CH₃OH]/[H₂CO]) in comets and planet-forming systems.

References: [1] Mumma, M.J., Charnley, S.B., 2011, ARAA, 49, 471; [2] Eistrup, C., C. Walsh, & E. F. van Dishoeck, 2019, A&A, 629, A84; [3] Ceccarelli, C., Caselli, P., Bockelée-Morvan, D., et al., 2014, Protostars and Planets VI, ed. H. Beuther, R. S.719 Klessen, C. P. Dullemond, & T. Henning, 859–882; [4] Lippi, M., et al., 2021, AJ, 162, 74; [5] Dello Russo, N., et al., 2016, Icarus, 278, 301; [6] Walsh, C. et al., 2014, A&A, 563, 33; [7] Morbidelli, A. & H. Rickman, 2015, A&A, 583, A43; [8] Lippi et al. 2024, submitted to ApJL , currently under review; [9] Lippi, M., et al. (2023), A&A, 676, A105; [10] Lippi et al 2024, submitted to A&A, currently under review; [11] Läuter M., et al., 2020, MNRAS 498, 3995–4004.

How to cite: Lippi, M., Podio, L., Codella, C., Faggi, S., De Simone, M., Villanueva, G. L., Mumma, M. J., and Ceccarelli, C.: Unveiling the Chemical Origins of the Solar System through Ground-Based Infrared Spectroscopy of Comets, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-350, https://doi.org/10.5194/epsc2024-350, 2024.

Comets are relatively-pristine remnants of the original planetesimals that were ejected from the planetary region in the late stages of planetary formation. The Oort cloud comet C/2014 UN271, hereafter UN271, is ~140 km in diameter, large enough that it could be an intact example of a planetesimal that formed in the protoplanetary disk before being ejected into the Oort cloud. UN271 is currently beyond 17 au from the Sun as it moves to a perihelion distance of 11 au in 2031. Given its large heliocentric distance, the temperatures on and below its surface are too low for efficient sublimation of water ice. It is likely that its activity is driven by hypervolatiles such as CO or CO2 and not H2O. It is dynamically new on its first inbound trip to the Solar System's planetary region providing the rare opportunity to study the volatile content of one of the original planetesimals in a pristine state. We present JWST/NIRSpec prism IFU observations of UN271 with R~100 covering the spectral range where we can detect emission features from the vibrational bands of the gas-phase all the main volatiles found in comets (such as CO2, CO and C2H6). Moreover, this range also includes absorption bands of solid-phase water-ice grains. Our observations, taken on December 22, 2022, when the comet was at 18.6 au from the Sun, provide constraints on the comet's CO and CO2 production rates, the activity driving mechanism, the presence and nature of water-ice grains in its coma and can be compared with similar spectra of Kuiper Belt bodies. We will discuss the implications for the timing of the formation of the original planetesimals as well as UN271's formation environment within the primordial Kuiper Belt.

How to cite: Bolin, B.: The volatile content of giant Oort cloud comet C/2014 UN271 during its return to the planetary region., Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-38, https://doi.org/10.5194/epsc2024-38, 2024.

How to cite: Kim, Y., Bauer, J., Masiero, J. R., Mainzer, A. K., and Gicquel, A.: CO+CO2 Production in Comet C/2020 F3 (NEOWISE) using NEOWISE detections., Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-594, https://doi.org/10.5194/epsc2024-594, 2024.

In terrestrial, carbon-based biochemistry, heteroelements such as oxygen, nitrogen, sulfur, and phosphorus play crucial roles as they introduce specific chemical functionalities in organic (hydrocarbon-based) molecules. The debate about the origin and evolution of life on Earth and possibly elsewhere requires a detailed understanding of (1) where and how organic chemical complexity emerges in space and (2) what exogenous materials may have been delivered to the early Earth through impacts, see, e.g., Rubin et al. (2019). Comet studies enable investigation of both aspects as these small bodies possess an organic-rich material record dating back to the earliest history of our Solar System and were an exogeneous contributor of volatile species to Earth (Marty et al. 2017).

ESA’s Rosetta mission visited and accompanied comet 67P/Churyumov-Gerasimenko (hereafter 67P) for two years and during a large part of the comet’s orbit around the Sun. Rosetta analyzed the comet’s chemical composition in unprecedented detail. A key instrument was the high-resolution Double Focusing Mass Spectrometer (DFMS) – part of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA; Balsiger et al. 2007). It unveiled a surprising organic chemical complexity: Relying on reference spectra, either calibrated or from the database of the National Institute of Standards and Technology, Hänni et al. (2022) showed how the extremely complex cometary mass spectrum is fully deconvolved. After detailed investigation of the pure hydrocarbon species (Hänni et al. 2022) and the O-bearing organic molecules (Hänni et al. 2023), our current work focuses on the N-bearing compounds. The heteroelement N is common in biomolecules such as amino acids and nucleobases and responsible for their characteristic biochemical functionality. To date, only a few N-bearing complex organic molecules have been identified in comets, one of them being the simplest amino acid glycine (C₂H₅NO₂), which was reported by Altwegg et al. (2016) after a targeted search. Here, we present a non-targeted, full analysis of the N- and NO-bearing complex organics and compare them to N-bearing molecules in meteorites, other comets, and the interstellar medium.

Rubin et al. ACS Earth Space Chem. (2019) 3, 1792−1811.

Marti et al. Science (2017) 356, 6342, 1069-1072.

Balsiger et al. Space Sci. Rev. (2007) 128, 745-801.

Hänni et al. Nat. Commun. (2022) 13, 3639.

Hänni et al. Astron. Astroph. (2023) 678, A22.

Altwegg et al. Science adv. (2016) 2, e1600285.

How to cite: Hänni, N., Altwegg, K., Baklouti, D., Combi, M., Fuselier, S., De Keyser, J., Müller, D., Rubin, M., and Wampfler, S.: N-bearing complex organic molecules in comet 67P, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-722, https://doi.org/10.5194/epsc2024-722, 2024.

How to cite: Doriot, A. C., Altwegg, K., Berthelier, J.-J., Bonny, R., Combi, M., Hänni, N., De Keyser, J., Müller, D., Fuselier, S., Rubin, M., and Wampfler, S.: Measuring the 34S/32S isotopic ratio in CS2 at comet 67P/Churyumov–Gerasimenko, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-421, https://doi.org/10.5194/epsc2024-421, 2024.

In 2014, the Rosetta space probe delivered its lander module Philae to the nucleus of comet 67P/Churyumov-Gerasimenko. After a non-nominal landing, instruments onboard Philae had very limited time and energy to operate. After the initial touchdown (supposed to be the only one) on the surface of the comet, COSAC, a Gas Chromatograph coupled to a Mass Spectrometer (GC-MS) embarked on Philae, took an automated mass spectrometric measurement. This data was produced during the bounce, and revealed a clear signal with intensity and diversity far greater than what was seen in the several blanks taken until this point. This signal was shown to come from excavated material from the surface which, at the moment of impact, entered the mass spectrometer’s chamber through its exhaust port located underneath Philae’s body. This data therefore represents the first ever sampling of a cometary nucleus. The core of this limited dataset is a single mass spectrum containing a mixture of unknown volatile molecules coming from the nucleus of the comet. The COSAC team published a deconvolution of this mass spectrum in 2015, identifying 16 organic molecules [1]. We revisited this dataset and applied a newly developed deconvolution method tailored for this specific and unusual problem [2]. We reduce the “clearly identified” pool of molecules to 12, including 3 new molecules never detected before on a comet (Figure 1 and 2).

Once at rest on the comet, using the very last of Philae’s available power, a drilling sequence was launched in the hope of feeding material from the surface of the comet to the analytical laboratory onboard the lander. COSAC was given priority for its analysis as it was the only instrument capable of chiral separation. A full GC-MS science sequence was launched on the COSAC instrument in the hope of obtaining a precise chemical composition of the nucleus of 67P. Unfortunately, due to the awkward position of Philae on the surface, the drill of the SD2 instrument did not penetrate the ground and very little to no material is believed to have been provided to COSAC. Here we show that although the landing and sampling were not nominal, the COSAC instrument worked as expected and produced a 17-minute gas chromatogram comprised of 421 individual mass spectra. We present an in-depth analysis of this previously unpublished gas chromatogram, the first and only one of its kind acquired on a comet for the foreseeable future [3]. We put forward the possibility of a small signal coming from ethylene glycol, a molecule also detected in the deconvolved COSAC mass spectrum (Figure 2, molecule highlighted in blue).

Figure 1. Individual color-coded contributions of the 12 molecules found in this research to the COSAC mass spectrum.

Figure 2. Comet 67P/Churyumov-Gerasimenko and a 3D visualization of the 12 organic molecules identified by this research: water, methane, carbon monoxide, hydrogen cyanide, methylamine, acetaldehyde, acetone, formamide and ethylene glycol are all confirmations from the original analysis of the mass spectral data. Additionally, 3 new molecules were found (in yellow): 2 methoxy compounds and cyclopentanol, all of which were not detected before on a comet. Image of the comet: ESA/Rosetta/MPS for OSIRIS Team PS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA

[1] Goesmann, F. et al. Organic compounds on comet 67P/Churyumov-Gerasimenko revealed by COSAC mass spectrometry. Science 349, aab0689 (2015).
[2] Leseigneur, G. et al. ESA’s Cometary Mission Rosetta—Re-Characterization of the COSAC Mass Spectrometry Results. Angewandte Chemie International Edition 61, e202201925 (2022).
[3] Leseigneur, G. et al. COSAC’s Only Gas Chromatogram Taken on Comet 67P/Churyumov-Gerasimenko. ChemPlusChem 87, e202200116 (2022).

How to cite: Leseigneur, G. and Meierhenrich, U.: New analysis of COSAC data from the Rosetta mission, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1075, https://doi.org/10.5194/epsc2024-1075, 2024.

Abstract:

Comet 67P/Churyumov-Gerasimenko, hereafter referred to as 67P, reached perihelion at 1.21 au on 12 November 2021. We observed  it over 15 observational epochs pre- and post-perihelion, using the Multi-Unit Spectroscopic Explorer (MUSE) integral field unit spectrograph, mounted at the Very Large Telescope (VLT). These observations captured the evolving gas-dust coma in sub-arcsecond detail, across a wide field of view, roughly 55''x55'', at 0.2''/pixel (~60-360km/pixel) sampling. We probed the inner, middle, and outer coma (ρ=10³-10⁵ km) from 2.25 au on the first observation in May 2021, to 1.28 au near-perihelion in late September 2021, and to 1.9 au post-perihelion by March 2022. Here, we present a full morphological and spectroscopic analysis of the gas-dust coma, including dust colour maps, molecular coma species maps, and gas production pathways, with clear detections of strong emissions from C₂, NH₂, and CN gas species. 

Introduction:

Visited by the ROSETTA orbiter, comet 67P is among the most well-characterized small-bodies in the Solar System and is a prime target for long-term evolutionary monitoring. The nucleus is bilobate in structure, joined by a thick neck about which the comet rotates at a 58° obliquity, which causes strong seasonal variability (Motolla et al. 2014). The two lobes, and neck, host a diverse range of morphological features and units, likely created by prolonged activity. As shown by Sierks et al. (2015), the smooth northern region of the neck, designated Hapi, is responsible for the majority of activity on the comet, however, smaller active regions are also seen throughout the northern hemisphere. Seasonal and diurnal effects further influence this activity. As 67P approaches perihelion, the subsolar point migrates to the southern sky after equinox. It illuminates previously shaded reservoirs of icy grains and material, which instigates more energetic activity and new volatile sublimation trends, not unlike like the twin outbursts recorded on 29 October and 17 November 2021 (Sharma et al. 2021) and enhanced CN coma (Opitom et al. 2019). Diurnal changes in insolation primarily influence volatile sublimation due to thermal lag into the subsurface reservoirs. Water ice is most strongly affected by thermal lag, as deposits can be as shallow as a few mm (Marboeuf et al. 2014), while more volatile species, like CO₂ and CO, are more heavily insulated by their greater depth (Hässig et al. 2015). With this context, we aim to analyse our MUSE dataset by isolating the dust, C₂, NH₂, [OI], and CN spectral features in our datacubes, from which we can probe the majority of the coma, its trends, and relations to the nucleus around 67P's 2021 perihelion.

Observing:

We observed 67P with the MUSE integral field unit (IFU) spectrograph, which collects three-dimensional datacubes, comprising two spatial and one spectral dimension (x,y,λ). These ground-based MUSE observations were collected over almost a year, from 15 May 2021 to 09 March 2022, as a part of ESO programmes 105.2086.001 and 108.223B.001. We utilised MUSE in the wide field mode (WFM) without adaptive optics, covering 4800 to 9300Å with an average resolving power of 3000 (Bacon et al. 2010). We exposed MUSE for 600 seconds using non-sidereal tracking and ensured comprehensive coverage through dithering and rotating observations by 90° from North to East between exposures, to minimize detector artefacts. The sky observations were positioned 5 to 10 arcminutes away from the system to ensure no contamination from the diffuse coma. We also conducted standard star observations for flux calibrations. The complete dataset (67P, sky, standard star) was reduced with the ESO MUSE Pipeline (Wielbacher et al. 2020) and ESO Molecfit Package (Smette et al. 2015).

Analysis:

To understand the dynamics of the gas and dust in the coma, we first reduced all datacubes and corrected for telluric absorption on a nightly basis, which significantly improved our detections of the C₂ (0,0) Swan band (~5100Å), NH₂ bands (~6000-7400Å), and the CN (1,0) Red band (~9100-9300Å). We ensured a satisfactory fit, and proceeded with the isolation of gas species via a dust and solar continuum removal technique described in Opitom et al. (2019). We utilized a reference 67P MUSE spectrum in which no gas species were detected to fit and subtract the dust continuum from each spectrum in our datacubes, iteratively. We used these dust-free cubes to isolate C₂, NH₂, and CN emissions and create maps of the molecular coma for all dates, sampled in Figure 1. We employ azimuthal median enhancement to our maps to enhance the substructure of each gas component. 

Fig. 1: Top panels: continuum-subtracted spectrum from 40'' circular aperture around 67P, on 30 September 2021. Dashed-red line is ideal continuum subtraction, solid black line is gas emission, solid red region is flux used to create maps. Lower panels: species maps of 67P coma. Red X is comet optocenter, red arrow is comet rotation axis and North pole direction, yellow arrow is sun angle, green arrow is velocity angle. 

Throughout the campaign, we saw strong C₂ coma emissions, primarily pre-perihelion, and sometimes filling the entire FoV (ρ>5x10⁴km). NH₂ coma emissions were equally prominent and persisted after perihelion, and only began to weaken by our last observations in March 2022. Additionally, NH₂ emissions did not always share the same morphology and orientation as the C₂ and dust coma, perhaps hinting at the existence of extended sources via ammoniated icy grains - to be tested by Haser models. CN was not robustly detected before August 2021, which is congruent with the expected sublimation after the southern vernal equinox passage the month prior. Post-equinox, we saw the expansion of the CN coma, which lasted until a few months after perihelion. Finally, dust colour largely followed expected sorting trends, becoming bluer at larger cometocentric distances. Further modelling to derive species scale lengths, production rates, and relations to the nucleus are underway.

How to cite: Murphy, B., Opitom, C., Snodgrass, C., Knight, M., and Yang, B.: Gas-Dust Coma Dynamics of Comet 67P/Churyumov-Gerasimenko during its 2021 Perihelion via VLT/MUSE, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-628, https://doi.org/10.5194/epsc2024-628, 2024.

Introduction

Comets are pristine relics of the early Solar System, formed from the agglomeration of icy grains and dust particles, offering insights into the evolution of the protosolar nebula (PSN). Despite their usual water-ice richness, the blue comet C/2016 R2 (PanSTARRS) exhibited atypical abundance ratios, with an H2O/CO upper limit of less than 0.32% [1], weak CN lines [2], and an exceptionally high N2/CO ratio of 0.09 [3], suggesting unique formation conditions. Our study revisits historical observations of a historical blue comet, C/1908 R1 (Morehouse), utilizing high-precision scanning technology from the New Astrometric Reduction of Old Observations (NAROO) project [4], combined with numerical integration techniques, to reevaluate its dynamical history and spectroscopic data in order to determine the extent of its similarities with C/2016 R2.

Dynamical history

Using two independent dynamical models, MERCURY and REBOUND, we investigated the past trajectory of comet C/1908 R1 by simulating 1000 clones derived from its orbital covariance matrix. Both models revealed that C/1908 R1 has no close encounters with the giant planets, and had likely been stored in the Oort cloud at about 100,000 au, supporting its classification as a dynamically new comet. Despite a hyperbolic orbit with an average eccentricity of 1.16 ± 0.27, the calculated excess velocity v∞ of 0.83 km/s is much lower than those of known interstellar objects, reinforcing its Solar System origin. We compared this to C/2016 R2's dynamical history [5], but while C/1908 R1 remained dynamically isolated, C/2016 R2 experienced significant gravitational interactions with Jupiter, resulting in a chaotic and unpredictable orbit, though likely an Oort cloud origin.

Spectroscopic analysis

We were able to obtain access to historical photographic plates of Comet C/1908 R1 preserved at the Meudon Observatory, covering observations from October 16 to November 29, 1908, including early spectroscopic data by A. de la Baume Pluvinel [6,7] and A. Bernard [8] from the Juvisy and Meudon observatories, respectively. These were digitized using the NAROO center's high-precision scanner (Fig.1). Despite the historical nature of the data and inherent challenges such as lack of historical information, potential atmospheric extinction misestimation due to lack of standard star identification in some cases, non-linear response of the photographic plates, and optical aberration from the objective prism, we were able to produce high-quality FITS files for detailed analysis and modeling. Spectral extraction involved calibrating wavelength using lines from the comet or reference stars and conducting flux calibration with standard stars such as Vega and Capella. We determined the N2+/CO+ ratios for the combined nights of October 31 and November 1, achieving a fit with a ratio of 7.7%, and on November 28, a slightly lower ratio of 7.2%, indicating consistency in our spectral analysis despite variations in observational conditions and the quality of the plates. Moreover, the analysis confirmed the presence of weak CN bands and subdued dust emissions, traits shared with Comet C/2016 R2, suggesting a low dust-to-gas ratio and a unique evolutionary path for these bodies. These findings, coupled with the identification of previously unrecognized C3 emissions in historical spectra, underscore remarkable compositional similarities between C/1908 R1 and C/2016 R2, hinting at their classification within a rare comet type. However, the question about the exact water ice composition of C/1908 R1 remains open, due to observational limitations of the time.

Tail Morphology

Observations using early photographic methods documented rapid morphological changes in the comet’s tail, exhibiting cycles of brightening, mass ejection, and detachment (TDEs) [9]. We find a recurring interval of approximately 15 days, suggesting influences beyond mere nucleus rotation. These changes correlate with solar activity, as evidenced by concurrent auroral displays, highlighting the tail's sensitivity to solar wind due to its volatile and ionic composition.

Conclusions

Comet C/1908 R1 (Morehouse) presents a compelling study of a dynamically new object, preserved in a pristine state since its origins at the outer edge of the Oort cloud, highlighted by both dynamical models and spectral analysis. Dynamical simulations show no close encounters with giant planets, affirming its status as an untouched relic from the Solar System's early days, while spectral analysis uncovers a unique composition, rich in N2+ and CO+, similar to that observed in Comet C/2016 R2. Despite significant insights, the absence of definitive water ice data leaves its complete classification tentative. With the rarity of blue comets, these findings underscore the importance of integrating historical data with modern scientific techniques.

Figure 1: The 1908 spectral plate obtained on October 31 and November 1, 1908, when the comet was 1.07 au from the Sun (left) and the resulting modeling of the extracted spectrum (right), corresponding to the tail region. 

How to cite: Anderson, S., Rousselot, P., Jehin, E., Noyelles, B., Manfroid, J., Hardy, P., and Robert, V.: Comet C/1908 R1 (Morehouse) as a C/2016 R2 (PanSTARRS)-like comet, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-59, https://doi.org/10.5194/epsc2024-59, 2024.

INTRODUCTION

We present the results of our recent work investigating possible correlations between cometary composition and nucleus size, as detailed in Robinson et al. 2024. This work follows on from laboratory experiments and numerical modelling of comet nuclei thermal evolution by Malamud et al. 2022, who considered a pebble pile internal structure with a low thermal conductivity for the nucleus. In this scenario heat from radionuclide decay can build up within the nucleus and form a thermal gradient. This then drives the outward migration of volatile species until they reach a region where they condense out, are entrapped in an amorphous ice, or they are depleted from the nucleus altogether. Radiogenic heating is stronger for larger comet nuclei, as such one would expect the effects of internal differentiation to be stronger for larger comets. Therefore in this work we conduct an analysis of literature data for the presence of any correlations between cometary volatile abundance and nucleus size which may be explained by the predictions of Malamud et al. 2022.

METHODS

For this study we have gathered together a significant number of measurements of comet composition and nucleus size from the available literature. Comet composition can be estimated from spectroscopic and/or narrowband photometric observations which measure the strength of emission features in the coma which are associated with various volatile species. We focus on measurements in which the production rate of a given species is measured contemporaneously with that of the most abundant cometary volatile, H₂O. We therefore analyse the abundance ratio of a given volatile relative to H₂O, which helps to reduce the effects of changing levels of cometary activity. It is difficult to remotely measure the size of a comet nucleus, which is generally small in size (often km scale) and low albedo. Furthermore when the observing geometry is favourable the comet is generally approaching the warmer inner Solar System and so the nucleus is obscured by the coma. When the nucleus is inactive size can be estimated from photometric observations and an albedo, similar to asteroid size measurements. Likewise thermal observations can be combined with a thermal model to estimate nucleus size. The most accurate size estimates are made using radar observations and imaging from spacecraft flyby/rendezvous, but opportunities to obtain such measurements are rare and/or costly.

As such we searched the literature and gathered published measurements of volatile species abundance and nucleus size from surveys, compilations and targeted observations of single objects. For both properties we often found multiple measurements from different sources. In our analysis we selected a single source for each measurement. We did this to avoid biases from the combination of measurements obtained using a variety of techniques, however, this method ignores the possible variations in the property (e.g. changes in volatile abundance as a function of time/measurement technique). Regardless, in Robinson et al. 2024 we outline our selection criteria and the full dataset is available to enable indenopendent investigations by the community.

This dataset was used to search for possible correlations between the abundance of the main cometary volatiles and the size of the nucleus, as would be expected from the predictions of Malamud et al. 2022. The correlation of the data (in log-log space) was assessed using the Pearson correlation coefficient. We attempted to account for possible observational biases, such as heliocentric distance of the abundance measurement, when assessing the strength of each correlation.

RESULTS AND SUMMARY

In our analysis we found a statistically significant correlation between cometary CO/H₂O abundance and nucleus size. This trend remains when only compositional measurements within 2 au are considered. Furthermore, bootstrap/jack-knife statistical resampling tests indicate that this trend is not overly dominated by a particular comet. We show that the CO/H₂O trend is compatible with a simple adaptation of the Malamud et al. 2022 theoretical model, whereby CO enrichment occurs via outward migration of CO gas followed by entrapment in an outer amorphous ice layer. For some volatile species we found only weak correlations that are not robust for the given data, for others there was no indication of correlation at all.

This work highlights the need for more measurements of the physical properties of comets, namely composition and size. More accurate measurements for more objects, ideally obtained in a homogeneous and consistent manner, would enable future studies to probe these initial findings in greater detail. The literature data is particularly lacking measurements for larger comets. With more data one could more accurately account for biases in observation and/or comet population (regarding dynamical evolution and thermal history for example). It is hoped that continuing community effort and future state of the art facilities will greatly increase the size and quality of measurements of cometary physical properties.

The full database of comet composition and nucleus size measurements compiled in this work is available online for the use of the community (see Robinson et al. 2024 and https://doi.org/10.7488/ds/7723).

Figure 1: Log scale plot of cometary CO/H₂O abundance against nucleus size. Only composition measurements taken within a heliocentric distance of 2 au are considered here, in an attempt to reduce observational bias. Marker colour denotes heliocentric distance of the composition measurement and marker shape indicates dynamical class (square - ecliptic comets, triangular - nearly isotropic comets). The presence of a correlation is indicated by a linear fit to the data (in log-log space) for the whole dataset (solid line).

Figure 2: The CO/H₂O abundance versus nucleus size from figure 1 is replotted (circular markers). The curves indicate the predictions of the adapted Malamud et al. 2022 model, where each curve indicates a different formation time. The other parameters used in this thermal model are: mineral fraction = 1, pebble radius = 0.1 cm, and permeability = 1.

REFERENCES

Malamud, Uri, Wolf A Landeck, et al.. ‘Are There Any Pristine Comets? Constraints from Pebble Structure’. MNRAS 514, no. 3 (23 June 2022): 3366–94. https://doi.org/10.1093/mnras/stac1535.

Robinson, James E, Uri Malamud, et al.. ‘A Link between the Size and Composition of Comets’. MNRAS, 28 March 2024, stae881. https://doi.org/10.1093/mnras/stae881.

How to cite: Robinson, J., Malamud, U., Opitom, C., Perets, H., and Blum, J.: A link between the size and composition of comets, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-415, https://doi.org/10.5194/epsc2024-415, 2024.

Introduction:

Roughly a hundred comets approach perihelion annually, yet only a fraction undergo thorough study due to the scarcity of observation time on larger and fewer available telescopes. However, comets are known to exhibit unpredictable variations for diverse reasons. Consequently, observing them on a restricted number of nights may yield a biased understanding of their evolution and composition. Acquiring homogeneous physical data from a broad sample is crucial for comprehending the distribution of their physical and chemical properties.

In this work, we present results from long-term photometric monitoring and some epochs from spectroscopic observations of four long-period comets (LPCs) and four dynamically new comets (DNCs) obtained between 2013 and 2024. These comets include C/2017 T2 (PanSTARRS), disintegrated comet C/2019 Y4 (ATLAS), the very bright comet C/2020 F3 (NEOWISE), C/2020 M3 (Atlas), C/2012 K1 (PANSTARRS), C/2018 W2 (Africano), C/2020 V2 (ZTF), and C/2021 S3 (PANSTARRS).

Our work contributes to the understanding of the cometary behavior of these two dynamical classes originating from the Oort Cloud which could be used for predictions of future comet observations or help to identify potential targets for future ESA Comet Interceptor mission [1].

Photometry (TRAPPIST):

We used both TRAPPIST-North (TN) and –South (TS) [2], to observe and follow those LPCs and DNCs along their orbits. These telescopes are equipped with standard Johnson-Cousin B, V, Rc, and Ic filters, as well as narrow-band filters CN, C₃, C₂, NH, and OH to compute the production rates (Qs) from the gas species and BC, GC, and BC to compute the dust proxy (Afρ) for the dust continuum [3].

Spectroscopy (HFOSC/HCT and LISA/MIRO):

Low-resolution long-slit spectra were acquired with the Himalaya Faint Object Spectrograph and Camera (HFOSC) [4], installed on the 2m Himalayan Chandra Telescope (HCT), and the 1.2 m telescope of the Mount Abu Infrared Observatory (MIRO), with the assistance of the Long slit Intermediate resolution Spectrograph for Astronomy (LISA) [5].

Figure 1: BVRI magnitude within radius aperture of 5" as a function of days to perihelion for comets C/2017 T2, C/2018 W2, C/2020 F3, C/2020 M3, and as a function of days to the disintegration for comet C/2019 Y4.

*The magnitude formula: m = M₀ + 5 log(r_g) + 2.5 n log(r_h).

Table 1: TRAPPIST observational circumstances and dynamical types of the comets reported in this work. All the orbital elements are taken from the NASA JPL/Horizon database.

Figure 2: The Optical spectrum of comets C/2017 T2, C/2018 W2, C/2019 Y4, C/2020 F3, and C/202 M3. For the disintegrated comet C/2019 Y4 (ATLAS), Top: Optical spectrum of 19Y4 before disintegration on 2020-02-23; middle: during disintegration on 2020-03-15, and bottom: after disintegration on 2020-05-26.

Acknowledgments

TRAPPIST is a project funded by the Belgian “Fonds National de la Recherche Scientifique” (F.R.S.-FNRS) under grant T.0120.21. This work is supported by the BIPASS program from the International Division of the Department of Science and Technology (DST; Govt. of India) and the Belgian Federal Science Policy Office (BELSPO; Govt. of Belgium). acknowledges support for the grant from the Academy of Research and Higher Education (ARES).

References:

[1] Jones, Geraint H et al. 2024, The Comet Interceptor Mission.

[2] E. Jehin et al. 2011, The Messenger, 145, 2-6.

[3] Farnham, T., Schleicher, D., & A’Hearn, M. (2000), Icarus, 147, 180.

[4] Aravind, K et al. 2021. Mon. Not. R. Astron. Soc. 502 (3), 3491–3499.

[5] Venkataramani, K., 2019. Optical Spectroscopic Studies of Minor Bodies of the Solar System (PhD Thesis).

How to cite: Hmiddouch, S., Jehin, E., Jabiri, A., Moulane, Y., Krishnakumar, A., Vander Donckt, M., Ahuja, G., Benkhaldoun, Z., and Ganesh, S.: Long-term TRAPPIST monitoring of a few Long Period and Dynamically New Comets., Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1139, https://doi.org/10.5194/epsc2024-1139, 2024.

Cometary dust, in detail, is a mixture of mineral and organic components (Guilbert-Lepoutre, et al., 2015; Prialnik, et al., 2004). As volatiles are released or sublimate, they drag out some dust particles. Together, they form a coma around the nucleus (Fulle, 2004). When we observe a comet, the light registered from the coma is a combination of solar light scattered by dust particles and gaseous emissions (Rosenbush, et al., 2020). However, at larger heliocentric distances, the latter can be negligible or absent (Ivanova, et al., 2019; Korsun, et al., 2008). It allows us to study the microphysical properties of dust particles using broadband photometry.

One of the basic photometric characteristics connected to dust is photometric color. The dust color is independent of the amount of dust particles in the coma and is defined by their physical and chemical characteristics, namely, size and chemical composition (Luk`yanyk et al., 2019; Betzler et al., 2017). Recent works of various authors show that the dust color may reveal significant variations, which sometimes can occur in a few days or weeks (Luk`yanyk, et al., 2019; Ivanova, et al., 2017). Still, changes in dust color remained poorly addressed. Predicting the color-change occurrence is impossible, so only continuous monitoring can be used for their study.

So, we aimed our work at searching for short-term (a few days or weeks) dust color variations of comets beyond 3 au from the Sun. The primary source of our data is the Skalnaté Pleso Observatory, with the 1.3-m Cassegrain-Nasmyth and 0.61-m Newtonian reflecting telescope. We used both archived and recently collected data. Additionally, we have obtained some observations at the Terskol Observatory using the 0.6-m Zeiss telescope and 6-m BTA SAO.

We have obtained data for 5 long-period comets, 5 hyperbolic comets, and 1 short-period comet 29P/Schwassmann-Wachmann 1. The latter is known for its continuous activity with outbursts, which provoke color changes. We have registered dust color variations using observations during two outbursts in October 2018 (Voitko, et al., 2022) and November 2020. Among other comets, we have found dust color variations from red to neutral or blue (or vice versa) for 3 long-period comets C/2016 M1 (PanSTARRS) (Voitko, et al., 2024), C/2017 T2 (PanSTARRS), and C/2016 N4 (MASTER) and hyperbolic comet C/2020 V2 (ZTF). Interestingly, the activity of these objects was relatively stable, with no outbursts. Hyperbolic comet C/2020 S4 (PanSTARRS) deserves a separate mention as it revealed some changes in dust color during its perihelion passage, but they were not as quick as we are looking for. It appears that 5 of 11 considered objects reveal dust color variations. To estimate dust properties, we used the model of agglomerated debris particles. It showed that changes in dust chemical composition are the main cause of color variations. In particular, a higher abundance of water-ice or Mg-rich silicate particles in the coma can induce a blue or neutral dust color. In contrast, Fe-Mg silicates and organics usually cause red color. However, we do not exclude the dependence of color from the size of dust particles. Our statistics are currently relatively sparse. Nevertheless, they show that dust color variations can be found in monitoring data. We also supplement our findings with the results from the literature to better understand the frequency of occurrence and possible mechanisms.

Acknowledgments

Our work was supported by the Slovak Grant Agency APVV no. APVV-19-0072, the Slovak Grant Agency VEGA 2/0059/22, and Doktogrant no. APP0363.

References

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Fulle, M. 2004. Comets II, pp. 565-575.
Guilbert-Lepoutre, A., et al. 2015. SSR, Vol. 197, 1-4, pp. 271-296.
Ivanova, O., et al. 2017. MNRAS, Vol. 469, 3, pp. 2695-2703.
Ivanova, O., et al. 2019. A&A, Vol. 626.
Korsun, P. P., Ivanova, O. V. and Afanasiev, V. L. 2008. Icarus, Vol. 198, 2, pp. 465-471.
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How to cite: Voitko, A. and Ivanova, O.: Rapid dust color variations of comets beyond 3 au, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-460, https://doi.org/10.5194/epsc2024-460, 2024.