SB10
Comets are primitive bodies, and therefore their detailed characterization is a key objective to probe the early stages of Solar System formation. The combined efforts from Earth-based observations, space missions, and modelling have revealed a class of bodies very broad in terms of physical and dynamical properties.
We invite contributions from all related topics, covering findings about all aspects of comets, as regarding their nucleus, coma, dust, and plasma properties, as well as international programs for their observations. We welcome presentations that explore and model data collected by past space missions, as well as presentations of upcoming ones, such as the ESA-led Comet Interceptor.
We encourage contributions that explore comet formation and evolution, in relation to general models of the Solar System, fostering lively discussions and collaborations between colleagues working on similar problems for different classes of objects (e.g. dust release from Active Asteroid vs Jupiter Family Comets vs outbursts of Centaurs). In particular, we encourage contributions that explore the continuum of small bodies and the overlap between different populations and look forward to an exciting set of talks about ground based observations and recent/future space missions.
Session assets
Abstract
Near perihelion, when comet 67P was most active, the Rosetta spacecraft resided inside the comet induced magnetosphere. The solar wind magnetic field was still present, but the solar wind ions were mostly gone, Rosetta was in the solar wind ion cavity. The solar wind was not completely gone though, there were sporadic occurrences of solar wind ions. Observations from this period could thus shed light on the solar wind - comet interaction for a medium activity comet. Solar wind ions with a broad energy and angular distribution would indicate a fully developed cometosheath pushed closer to the nucleus. We present the first results from a study of all detected sporadic events.
Introduction
The Rosetta spacecraft followed comet 67P from August 2014 to end of September 2016. This covered heliocentric distances from more than 3 AU down to a comet perihelion at 1.2 AU. The comet activity and thus also the comet gas and plasma cloud expanded significantly as the comet approached perihelion. From May 2015 to the end of 2016 the Rosetta spacecraft was mostly well the solar wind ion cavity, a region devoid of solar wind ions (Behar et al. 2017). RPC-ICA identification of ion species was based on a manual inspection of daily mass channel data. Very sporadic occurrences of the solar wind that did not stand out over the noise level in this daily summed data is missing from the level 4 mass separated data set in the Planetary Science Archive.
Method
The solar wind ion occurrences we report here were too short-lived to be seen in daily averages. They are not present in the standard mass separated data set delivered to PSA. An automatic algorithm was used to detect potential cases. A total of 285 ion velocity distributions with potential solar wind ions around perihelion were found and manually inspected. Of these 174 passed the manual inspection. We used a selection criteria of at least 20 counts detected within the solar wind ion mass channels (H+, He2+ and He+) in one energy level and azimuthal sector. A sample inspection figure is shown in Fig. 1 with data from May 28 2014. The lower left panel shows the “energy- mass matrix” with mass channel (anode) on the x-axis and energy (eV) on the y axis. Protons are seen at mass channels 26 and 27. The ions at lower mass channels are water ions. This panel is the most important to verify that we indeed see H+ and He2+ and not water ions of cometary origin.
Figure 1: An example of the data figures used to inspect potential cases of sporadic occurrence of solar wind ions in the time period when Rosetta was mostly inside the solar wind ion cavity, from May 2014 to and of 2016. The upper left panel shows solar wind ion counts summed over all energies as function of sector corresponding to azimuths of 0°-360° (x-axis), and elevation from approximately -45° to +45° from the instrument symmetry plane (y axis). The upper left panel shows solar wind counts as function of sector and energy channel. The lower left channel shows the ion counts as function of mass channel (x-axis) and energy in eV (y-axis). The lower right panel is a line plot of solar wind ion counts as function of energy. The sample data is from 28 May 2015 at 05:58 UT.
Results
We do see broad energy distributions of protons at times. This indicates that the solar wind pushed the cometosheath closer to the nucleus for these cases. Usually the angular width of the signal is not more than three sectors of 22.5° width. A more careful analysis will be made to see if this fits expectations of a fully developed cometosheath.
The next step in the analysis is to look at the data in a better field of view plot as we did in Moeslinger et al (2023). This is shown in Fig. 2. The upper panel shows flow directions and fluxes of cometary ions with energy above 40 eV, the lower panel shows solar wind ions. One can see that solar wind ions are seen in the lower half of the field of view, cometary ions in the upper half. Both species are coming from somewhere in between the sun (yellow dot) and the comet nucleus (grey star).
Figure 2: Plot of cometary ions (upper panel) and solar wind ions (lower panel) in the RPC-ICA field of view. The colour indicates the median energy and the intensity the logarithm of the particle flux. See Moeslinger et al. (2023) for more details on this type of plot.
At other cases the angular and energy extent of the observed ions were small, energies were often well below typical solar wind energies. What appeared to be almost undisturbed solar wind was seen on some occasions. On several occasions only H+ or only He2+ was seen in a narrow energy and angular range, reminiscent of reported observations of solar wind precipitation observed at Mars (Stenberg et al. 2011).
We put the observations in the context of the magnetic field data and other plasma data. We end by noting what implications our results have for a Comet Interceptor flyby of a moderately active comet like 67P at perihelion.
References
Behar, E., H. Nilsson, M. Alho, C. Goetz, B. Tsurutani, The birth and growth of a solar wind cavity around a comet - Rosetta observations, Monthly Not. Roy. Astr. Soc., 469, S396 – S403, 2017
Moeslinger, A., Wieser, G. S., Nilsson, H., Gunell, H., Williamson, H. N., LLera, K., et al. (2023). Solar wind protons forming partial ring distributions at comet 67P. Journal of Geophysical Research: Space
Stenberg, G., H. Nilsson, Y. Futaana, S. Barabash, A. Fedorov, and D. A. Brain, Observational evidence of alpha-particle capture at Mars, Geophys. Res. Lett., doi:10.1029/2011GL047155,, 2011
How to cite: Nilsson, H., Möslinger, A., and Stenberg Wieser, G.: Solar wind interaction with comet 67P around perihelion, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-328, https://doi.org/10.5194/epsc2024-328, 2024.
In this presentation, we explore photometric and polarimetric observations of the asteroids that became active either naturally or as a result of space experiments.
As an example of naturally active asteroids, we consider asteroid (248370) QN173, leveraging quasi-simultaneous data on color and polarization distribution along its tail reported in [1]. Through computer modeling, we analyze these data to unveil the characteristics of the dust particles. Utilizing irregular solid particles resembling material found on C-type asteroids, we employ the surface-integral-equation (SIE) method for particle sizes r ≤ 3 microns and the SIRIS4 code based on geometric optics approximation for particles larger than r > 3 microns. Our modeling reveals the size distribution of particles and their variation with distance to the asteroid and phase angle. Our findings suggest that in July 2021, at phase angle of 23°, dust particles exhibited a power-law size distribution with the smallest particles of radius 2.5 microns near the asteroid, decreasing to 1.6 microns at the distance of 60,000 km. In October 2021, at a phase angle of 8°, the size distribution near the asteroid had a power of 3.0 with the smallest particles of radius ~ 2.5 microns, while at 60,000 km distance, the power was 4.0 with the smallest particles of radius 0.8 microns. These results align with the dynamics of dust particles influenced by radiation pressure.
We also examine the dust ejected by asteroid Dimorphos following the impact of the DART spacecraft. Employing similar modeling techniques, we reproduce VLT FORS2 observations of polarization [2] and VLT MUSE observations of color [3] obtained for the same dates. The observations showed the absence of any trends in color and polarization with the distance from the impact; see Figure 1 which shows the polarization and color distribution in the tail on October 25, 2022. This indicated the dominance of particles larger than 100 microns that scattered light in the geometric optics regime. This limited our capability to study the variations in the dust properties along the observed tail. To extract more information about the ejecta particles, we considered several dates of observations, exploring the change in the dust size distribution with the time after impact. Utilizing the characteristics of size distributions obtained from the modeling, we analyze HST WFC3 images [4] for the same dates. This allows us to estimate the dust column density at varying distances from the asteroid facilitating estimation of the mass of the dust in the tail.
Acknowledgment. This work was supported by NASA DART Participating Scientist grant #80NSSC21K1131.
Figure 1. Polarization (left) and color (right) along the DART ejecta tail on October 25, 2022.
References
1. Ivanova, O., Licandro, J., Moreno, F., Luk’yanyk, I., Markkanen, J., Tomko, D., Husárik, M., Cabrera-Lavers, A., Popescu, M., Shablovinskaya, E. and Shubina, O., 2023. Long-lasting activity of asteroid (248370) 2005 QN173. Monthly Notices of the Royal Astronomical Society, 525(1), pp.402-414.
2. Gray, Z., Bagnulo, S., Granvik, M., Cellino, A., Jones, G.H., Kolokolova, L., Moreno, F., Muinonen, K., Muñoz, O., Opitom, C. and Penttilä, A., 2024. Polarimetry of Didymos–Dimorphos: Unexpected Long-term Effects of the DART Impact. The Planetary Science Journal, 5(1), p.18.
3. Opitom, C., Murphy, B., Snodgrass, C., Bagnulo, S., Green, S.F., Knight, M.M., de Léon, J., Li, J.Y. and Gardener, D., 2023. Morphology and spectral properties of the DART impact ejecta with VLT/MUSE. Astronomy & Astrophysics, 671, p.L11.
4. Li, J.Y., Hirabayashi, M., Farnham, T.L., Sunshine, J.M., Knight, M.M., Tancredi, G., Moreno, F., Murphy, B., Opitom, C., Chesley, S. and Scheeres, D.J., 2023. Ejecta from the DART-produced active asteroid Dimorphos. Nature, 616(7957), pp.452-456.
How to cite: Kolokolova, L., Markkanen, J., Ludet, Q., Ivanova, O., Gray, Z., and Opitom, C.: Characterizing the dust in active asteroids by modeling their photometric and polarimetric images, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-567, https://doi.org/10.5194/epsc2024-567, 2024.
Modern sky surveys now regularly discover comets at distances between 5 and 10 au, or even further, from the Sun. This is expected to become more common when the Vera C Rubin observatory’s Legacy Survey of Space and Time (LSST) begins in around a year. Yet the distant activity of comets is still poorly understood – at such distances the equilibrium temperature is too low for water ice sublimation to be the driving mechanism, as is thought to be the case at distances closer than 3-5 au. Sublimation of more volatile ices, such as CO or CO2, is a likely activity driver at larger distance, but the relative importance of these is unknown, and other mechanisms (such as phase change between amorphous and crystalline water ice) cannot be ruled out.
Observationally, we can constrain distant comet activity mainly through measurement of the total brightness of the comet. This will increase as it approaches the Sun, due to decreasing distance from the observer, and an intrinsic increase in the amount of material (and therefore reflecting area) in the coma. We typically describe the latter using the total heliocentric brightness of a comet, in magnitudes, as m = H(1,1,0) + 2.5n log(r), where H(1,1,0) is the absolute magnitude of the comet (its brightness at 1 au distance), r is the distance from the Sun, and n is a slope parameter (the activity index) that describes how quickly a comet brightens as it approaches. Historically, returning long period comets have been observed to have a larger n (i.e. a steeper slope, and more rapid brightening) than dynamically new comets (DNCs) entering the inner Solar System for the first time.
We will present results on long period comets observed over a wide range of distances as part of the LCO Outbursting Objects Key project (LOOK), what this means for comet detection with LSST, and ultimately how this will influence target selection for the ESA Comet Interceptor mission. The LOOK data gives us well calibrated photometry over a much larger range of heliocentric distances than has typically been possible (Holt et al. 2024; PSJ, submitted). This shows that a single slope parameter cannot be fit over the full range for most comets. Instead, a trend is seen of steeper slopes at larger distances (Fig. 1). The shallower slopes seen for DNCs are shown to be only an effect of older observations being limited to small distances: DNCs brighten rapidly at larger distances, and their activity plateaus as they reach the water ice sublimation region.
We suggest a new empirical model for comet brightening, where we replace the constant slope parameter n with a function that changes linearly with distance (r), n = ar + b, where a and b are fit coefficients. This model gives reasonable fits to the LOOK dataset (e.g., Fig. 2), and allows better prediction of future brightness of comets based on initial observations at large distance, relevant for Comet Interceptor. We will present the range of a and b parameters that we find, how these correlate with other comet parameters (such as absolute magnitude or dynamical type), and what this means for LSST predictions.
Fig 1: Change of activity index n with distance for LOOK sample (from Holt et al. 2024).
Fig 2: Example brightness measurement for comet C/2021 S3 (PANSTARRS), showing the change in slope with decreasing heliocentric distance, and the empirical fit, given by n = 0.31r -1.19 in this case.
How to cite: Snodgrass, C. and Holt, C.: The activity pattern of distant long period comets, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-324, https://doi.org/10.5194/epsc2024-324, 2024.
Introduction: Comet Interceptor is the first Fast (F-class) mission in ESA’s Cosmic Vision program [1], and is the first rapid response mission, waiting in space for its target comet to appear. Its goal is the first in situ investigation of a long-period comet. Comet Interceptor (Spacecraft A or S/C A) will carry two deployable probes, allowing multipoint investigations of the target. Probe B1 is contributed by JAXA and probe B2 by ESA. The mission will be launched in 2029 on an Ariane 6 towards the Sun-earth Lagrange point L2, together with the Atmospheric Remote-sensing Infrared Exoplanet Large-survey (ARIEL) mission.
Science Objectives: All space missions to comets have so far visited short-period comets (SPCs). Comet Interceptor will, for the first time, target a long-period comet (LPC), ideally a dynamically new one. The mission will investigate the processes of planetesimal formation by evaluating which of the phenomena observed by previous missions, particularly during the rendezvous of Rosetta with Comet 67P, are primordial and which have developed during the many perihelion passages of those SPCs. Specifically, the objectives of Comet Interceptor are:
- Comet Nucleus Science - What is the surface composition, shape, morphology, and structure of the target object?
- Comet Environment Science - What is the composition of the coma, its connection to the nucleus (activity) and the nature of its interaction with the solar wind?
Mission Profile: After launch and transfer to L2, Comet Interceptor will wait for its target comet. In the unlikely case that no suitable LPC is found, the target will be selected from a list of SPCs.
The comet encounter will take place near Earth’ orbit (between 0.9 and 1.2 AU from the sun), at the location where the target comet crosses the ecliptic. The duration of the waiting time (typically a few years) and of the transfer to encounter (typically between several months and a few years) depend on the target. The concept of the mission profile is illustrated in Figure 1.
Figure 1: Illustration of the mission profile. Comet Interceptor will be launched into a halo orbit around Sun-Earth Lagrange point L2. It will then be transferred on an interplanetary trajectory to encounter the target comet. Figure taken from [2].
In the last two days before the fast flyby (velocity between 10 km/s and 70 km/s) the probes will be released from S/C A and pass by the target. Comet Interceptor is designed to withstand the environment of Comet 1P/Halley at the time of the flyby by the Giotto mission at a speed of 70 km/s and a closest approach distances of 1000 km for S/C A, 850 km for probe B1 and 400 km for probe B2. The closest approach distances may be adjusted according to flyby velocity and target comet activity. The data from the probes are transferred to S/C A by an intersatellite link, and up to 6 months after the flyby are reserved for data downlink from S/C A to earth.
Payload: The instrumentation of Comet Interceptor is:
Spacecraft A:
- Comet Camera (CoCA): Visible high-resolution imager, 4 colour filters;
- Multispectral InfraRed Molecular & Ices Sensor (MIRMIS): IR Imaging spectrometer, 0.9 – 25 μm;
- Mass Analyzer for Neutrals in a Coma (MANiaC): Mass Spectrometer, mass/charge range up to ~1000;
- Dust, Fields, and Plasma (DFP-A) instrument suite: dust detector, magnetometer, plasma instrument measuring electric fields and plasma density and temperature, ion and energetic neutral atoms spectrometer, and electron spectrometer.
Probe B1:
- Hydrogen Imager (HI): Ly α imager;
- Plasma Suite (PS): Magnetometer and Ion Mass Spectrometer;
- Narrow Angle Camera (NAC) and Wide Angle Camera (WAC): NAC for high-resolution nucleus imaging, WAC for Coma imaging.
Probe B2:
- Entire Visible Sky (EnVisS): All-sky imager with polarimetric capability;
- Optical Periscopic Imager for Comets (OPIC): Visible Imager for science and navigation;
- Dust, Fields, and Plasma (DFP-B2): Dust detector and magnetometer.
Conclusions: The Comet Interceptor mission provides various firsts:
- First mission to an LPC,
- First multipoint investigation of a comet with three spacecraft,
- First rapid response mission.
References: [1] Jones, G. H. et al. (2024), Space Sci. Rev 220, issue1, article 9, doi:10.1007/s11214-023-01035-0.
[2] Snodgrass, C. and Jones, G. H. (2019), Nat. Comm. 10, 5418, doi:10.1038/s41467-019-13470-1.
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How to cite: Küppers, M. and the The Comet Interceptor Science Working Team: Comet Interceptor: A Rapid Response Mission To a Pristine World, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-213, https://doi.org/10.5194/epsc2024-213, 2024.
++ 1. Introduction
The Hayabusa2 spacecraft is currently cruising through deep space for the extended mission Hayabusa2#. The spacecraft is scheduled to flyby asteroid 2002 CC21 in 2026 and rendezvous with asteroid 1998 KY26 in 2031. Hayabusa2's VIS cameras include the ONC-T (Onborad Navigation Camera - Telescopic) and the wide-angle ONC-W1 and ONC-W2 (Figure 1). ONC-T, with its high sensitivity and multi-band observation capability, is the primary scientific instrument [1]. During the long cruise, ecliptic light observations [2] and exoplanet observations [3] continue as ONC-T observations. On the other hand, we are exploring ways to further utilize ONC cameras during the cruisng phase, and in this study, we examine how to utilize ONC-W2 and plan to process the data.
Figure 1. Schematic view of the configuration of ONC-T, W1, and W2 (after [4]). Blue line indicates the solar array paddle.
++ 2. Characteristics of ONC-W2
The disadvantages and advantages of using the ONC-W2 for distant objects are as follows.
[Disadvantages] Low sensitivity and stray light
- The sensitivity of the ONC-W2 is not sufficient to observe distant objects because it is designed to observe the surface of an asteroid with disk-resolved situation.
- The stray light from the multi-layer insulation at the edge of ONC-W2's FOV is very large for long exposure observation.
[Advantage] Wide range of observable direction
- The ONC-W2 camera can observe a wide area, whereas the ONC-T camera can only point in a narrow directions due to the limitations of the solar array paddle. Since the W2 camera faces the side of the solar array paddle (in the +Z direction of the spacecraft), it can cover 48% of the entire sky by turning the spacecraft attitude around the +Z axis and pointing the camera in different directions without losing power.
Due to its low sensitivity but wide field of view, W2 could be used, for example, to continuously observe bright new comets for several days or weeks. The most recent such possibility is the comet C/2023 A3 (Tsuchinshan-ATLAS). An example about the estimation of observable period is shown in Section 4.
++ 3. Preparation of data processing methods
New ONC-W2 applications will require additional tools different from those for Ryugu images. We are working on a list of necessary data processing methods and calibration tasks.
+ Stray light
Previous calibration studies have shown that the presence or absence of stray light in W2 depends on the attitude of the spacecraft [5]. When stray light does occur, the degree of stray light is significant (Figure 2). The primary countermeasure is to adopt an attitude that minimizes stray light, but it is also necessary to develop image processing methods to remove stray light.
Figure 2. An example of ONC-W2 long exposure (44.6s) image with stray light. White dots are mainly hot pixels.
+ Sensitivity check
The sensitivity of ONC-W2 prior to Ryugu arrival has been confirmed by [5]. However, because of sensitivity changes due to the Ryugu touchdown and changes over time, it is necessary to confirm the current sensitivity. As a quick check tool, we have prepared a method to estimate the sensitivity statistically from multiple stars. Figure 3 below plots the relationship between the stars V mag and integrated DN from 43 frames observed in 2016, with stray light removed. These stars include variable stars, but the effect is expected to be smaller by using a large number of stars.
Figure 3. Relationship between the stars Vmag and integrated intensity (DN) of long exposure (44.6s) images.
++ 4. Observation opportunities
We are also considering the preparation of methods and tools for narrowing down suitable observation opportunities for ONC-W2. The following is the case study of comet C/2023 A3.
Figure 4 shows the timing of the comet's entry into the FOV of ONC-W2. The orbit of the comet was obtained from JPL Horizons Sytem [6]. In this figure, the entire space as seen from the spacecraft is projected in a simple cylindrical projection. The spacecraft is oriented with the solar array paddle (+Z) pointing toward the sun and the W2 camera side toward the lower ecliptic plane. The red dots are the direction of the comet calculated every other day. The comet was found to cross the FOV from August 20 to August 28, 2024. Further observation will be possible by changing the attitude of the spacecraft.
Figure 5 shows the total magnitude of Comet C/2023 A3 as expected from the position of Hayabusa2, which is expected to be 2-3 magnitude at the end of August, bright enough to be observed by ONC-W2. At this time, the Earth is on the opposite side of the Sun, making it difficult to observe this comet. Therefore, observation of this comet by a spacecraft would be highly valuable as data. We plan to conduct an observational test with ONC-W2 during this period. We will present a preliminary report in this presentation.
Figure 4: Calculated timing of comet crossing in ONC-W2 field of view.
Figure 5. Predicted total magnitude of Comet C/2023 A3 from the position of Hayabusa2.
++6. Conclusion
We examine how to utilize Hayabusa2 ONC-W2 camera in the cruising phase. Due to its low sensitivity but wide field of view, ONC-W2 could be used to continuously observe bright new comets for several days or weeks. We plan to conduct an observational test of the the comet C/2023 A3 in August. We will present a preliminary report in this presentation.
++ Acknowledgement: We thank the Haybusa2# systems and science teams for discussing the feasibility of the operation.
++ References: [1] Sugita et al. (2019) Science 364, eaaw0422. doi.org/10.1126/science.aaw0422 [2] Tsumura et al. (2023) Earth Planets Space 75, 121. doi.org/10.1186/s40623-023-01856-x [3] Yumoto et al. (2024) 55th LPSC, Abstract 1774. [4] Kouyama et al. (2021) Icarus 360, 114353. doi.org/10.1016/j.icarus.2021.114353 [5] Tatsumi et al. (2019) Icarus 325,153-195. doi.org/10.1016/j.icarus.2019.01.015 [6] NASA JPL Horizons System. https://ssd.jpl.nasa.gov/horizons/app.html#/
How to cite: Yokota, Y., Kouyama, T., Morota, T., Sakatani, N., Sugita, S., Yamada, M., Tatsumi, E., Matsuoka, M., Hayakawa, M., Yumoto, K., Kawakita, H., Shinnaka, Y., Honda, R., Honda, C., Cho, Y., Kameda, S., Suzuki, H., Yoshioka, K., Sawada, H., and Ogawa, K.: Study on the possibility of comet observation using ONC-W2 camera during the cruising phase of Hayabusa2#, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-961, https://doi.org/10.5194/epsc2024-961, 2024.
The pristine nature of comets offers invaluable insights into the formation and evolution of the early solar system. Examining their morphological features is crucial for understanding their composition, activity, and dynamics. Here we used narrowband imaging to isolate emission lines, image enhancement to improve image contrast, and morphological analysis to investigate the morphological and temporal features of comet C/2006 P1 (McNaught), hereafter C/2006 P1, and its rotational period.
Comet C/2006 P1, renowned the 'Great Comet of 2007' captivated observers worldwide with its brilliant tail during its perihelion at 0.3 AU, particularly fascinating viewers in the Southern Hemisphere after its perihelion. Observing the comet immediately after its perihelion was challenging due to its proximity to the Sun. The advanced capabilities of the European Southern Observatory’s 3.6m New Technology Telescope (NTT), located at La Silla in Chile, were utilized to observe the comet during twilight when it was positioned at a very low elevation angle. Observations commenced on January 27, 2007, 15 days post-perihelion, extending until February 4, reaching the NTT's elevation limit of 10 degrees, with additional observations between February 25 and 28. Using the ESO Multi-Mode Instrument (EMMI), various observations totaling to 210 exposures, including imaging with both broadband (BV R) and 6 narrowband cometary filters, targeting emission lines of CN (386nm), C3 (405nm), C2 (510nm), NH2 (662nm), blue and red dust continuum (441nm and 683nm respectively) as well as spectroscopy. In this work we analyse the narrowband images.
We applied image enhancement methods to enhance the visibility of distinct features such as jets, fans, spirals, and arcs. Various techniques, including subtracting and dividing by azimuthal mean/median profiles, azimuthal renormalization and division by 1/ρ profile were tested and compared. Additionally, rotational filtering and the Larson-Sekanina filter were applied for comparison.
Morphological analysis of the enhanced images obtained through narrowband imaging revealed diverse characteristics within the comet's coma, illustrating the emergence and evolution of these features over time and with rotational orientation. Removal of azimuthal profiles technique, although very sensitive to centering of the nucleus, revealed fainter large-scale features such as spirals, arcs and jets on CN narrowband images. These jets evolve from spirals to arcs during the first observing run and eventually dominate as one or two linear and fan jets by the end of the second observing run.
Generally, subtracting or dividing by the azimuthal median profile does not introduce artifacts, and observing consistent features across tested techniques gives us confidence that the features are real.
Furthermore, periodic repetition of similar coma morphology in CN filters allowed us to constrain the nucleus rotation period. This was done first by dividing each subsequent images by each other to unveil temporal features, and computed their root mean square, RMS to determine the minima ie minima repeats with nucleus rotation. Images taken between 31st January to 4th February, and 25th to 28th February were selected separately, as they provided good but different temporal coverage epochs. Rotation state of the comet's nucleus is discussed.
Figure 1
Figure 2
Figure 1: Shows sample enhanced images of comet C/2006 P1 obtained between January 31 and Febraury 3, 2007 during the first observing run. Using division by azimuthal medium profile, the images reveal spirals, arcs, and linear jets, showing the emergence and evolution of these features as the comet’s nucleus rotates.
Figure 2: Images obtained on February 26-28 during the second observing run were enhanced using the same technique revealing a morphology dominated by linear and fan jets in the comet’s coma.
How to cite: Okoth, V., Snodgrass, C., and Opitom, C.: Narrowband Observation of Comet C/2006 P1 (McNaught) and Its Rotational Period through Morphological Analysis, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1001, https://doi.org/10.5194/epsc2024-1001, 2024.
Comets are among the most primordial objects of the solar system. According to Davidsson et al. (2016), they did not suffer from collisional processing, and remained mostly thermally unaltered since their formation, including by radiogenic heating. When a comet is injected into the solar system, either from the Oort cloud or from the Kuiper belt (e.g., Dones et al. 2004, Duncan et al. 2004), the above remains true for the nucleus deep interior but not for its upper surface, i.e. the first meters, which experiences a strong increase in insolation. This increasing insolation is the main driver for cometary activity and nucleus erosion (e.g., Whipple 1950).
In this work, we focus on the effects of insolation on comet 67P/Churyumov-Gerasimenko (hereafter 67P), the target of the Rosetta mission, over a complete revolution around the Sun. We aim to better understand the thermal environment of the nucleus of 67P: the temperature variations on the nucleus surface, erosion, connections with global and local topography, and how insolation affects the nucleus interior temperature for the presence of volatile species such as H2O and CO2.
For this work, we developed two thermal models, combined with the nucleus shape model of comet 67P (Preusker et al. 2017), to compute the nucleus surface and interior (the first meters) temperature over a complete revolution of 67P, i.e. 6.45 yr. Our first thermal model has a high spatial resolution of 300 000 facets and compute only the surface temperature, while our second thermal model has a lower spatial resolution of 10 000 facets but includes heat conductivity to compute the temperature inside the nucleus down to about 3 meters.
Figure 1 is a result of our first thermal model, and shows the maximum temperature reached over the orbit. Globally, the maximum temperature is the highest in the Southern hemisphere (SH) with 350 – 400 K, followed by the equatorial regions with 300 – 350 K, and then by the Northern hemisphere (NH) that is the coldest with 210 – 300 K. This directly reflects seasonal effects. Remarkably, cliffs in the NH (e.g., Seth region) are significantly hotter than the surrounding plains, by 50 – 100 K; their orientations allow a longer insolation when approaching the Sun and delay the beginning of the polar night close to perihelion. At the equator (e.g., Imhotep region), the cliffs facing South are hotter than the plains by 50 K, while the cliffs facing North are colder than the plains by 50 K. Overall, cliffs and plains behave differently due to their different orientation relative to the Sun. Finally, the maximum temperature is always higher than the sublimation temperature of water ice (180 K), therefore there exists no region on 67P where water ice is stable all around the orbit.
Figure 2 is a result of our second thermal model, and shows the maximum temperature reached over one revolution, at various depths: at the surface, at 5 cm depth (below the diurnal thermal skin depth) and at 1 m depth (below the seasonal thermal skin depth). At 5 cm depth, the temperature already drops significantly, down to 250 – 300 K in the SH and down to 150 – 200 K in the NH. The sublimation of water ice is still possible everywhere, excepted on the cliffs located on each side of the neck in the NH, and in large deep holes in the NH. At 1 m depth, temperature is even lower, from 70 – 100 K in the SH to 100 – 170 K in the NH. The sublimation of water is only possible in the Northern terrains located in the Ma'at and Ash region, facing North. Finally, the sublimation of CO2 ice is possible everywhere on the nucleus down to 1 m depth, since the temperature is always larger than 70 K. To summarize, inside the nucleus, the temperature is lower in the SH than in the NH, since the SH receives a short and strong pick of insolation at perihelion, which only heat superficially the nucleus compared to NH that is heated for a much longer time, so that the energy can penetrate deeper inside the nucleus.
The above results are just two examples of many scientific questions that can be address with our thermal models, and more examples will be shown at the conference.
References
Davidsson et al., 2016, A&A, 592, A63 432
Dones et al., 2004, in Comets II, 433 ed. M. C. Festou, H. U. Keller, & H. A. Weaver, 153
Duncanet al., 2004, in Comet II , 433 ed. M. C. Festou, H. U. Keller, & H. A. Weaver, 193
Keller et al., 2015, A&A, 583, A34
Preusker et al., 2017, A&A, 607, L1
Whipple, 1950, ApJ, 111, 375
Figure 1 – Maximum temperature (K) reached at the surface of 67P over one revolution. The results were obtained with our thermal model that has 300 000 facets.
Figure 2 – Temperature at various depths. The results were obtained with our thermal model that has 10 000 facets.
How to cite: Groussin, O., Jorda, L., and Attree, N.: The thermal environment of comet 67P/Churyumov-Gerasimenko, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-190, https://doi.org/10.5194/epsc2024-190, 2024.
Throughout the initial four years of the operative mission, METIS coronagraph [1] carried out numerous scientific observations, including some focused-on comets. Among the observed cometary targets, there are periodic comets, like 2P/Encke, sunskirters, such as 96P/Machholz (see Figure 1), some sungrazers [2] and even a long period comet, the C/2021 A1 (Leonard) [3], having an orbital period of approximately 80,000 years. Although many of these observations, especially of periodic comets, were specifically planned, some comets were also identified a posteriori on images collected for solar corona studies.
Figure 1: UV channel observation for the 96P/Machholz sunskirter comet during its transit in the METIS Field of View on January 30, 2023.
Metis is the coronagraph onboard SolO and it has been conceived to acquire images of the solar corona both in linearly polarized visible light (VL, 580–640 nm) and narrow-band (±10 nm) ultraviolet (UV) around the HI Lyman-a (121.6 nm) spectral line. Metis is the first coronagraph able to perform such simultaneous observations.
The instrument is designed to image the structure and dynamics of the full solar corona in an annular FoV covering the range from 1.6° to 2.9°, with a plate scale up to 10 “/px in VL channel and up to 20”/px in UV. Owing to the eccentricity of the spacecraft orbit, the heliocentric distances imaged are from 1.6 to 3.1 solar radii at minimum perihelion distance (0.28 au), up to the range from 6.0 to 12.0 solar radii when the spacecraft is around 1.0 au. A sketch of the raytrace of the two channels of the Metis coronagraph, i.e. the UV and VL, is given in Figure 2.
Figure 2: Metis layout. On the top: the UV path. On the bottom: the VL path [4].
The ability of METIS to perform simultaneous imaging in a narrow UV band around HI Ly-alpha and in the visible wavelength range can be highly impactful in cometary studies. UV images enable the study of neutral hydrogen coma morphology and the estimation of the water outgassing rate from the comet nucleus. Conversely, visible polarization images allow the derivation of comet parameters correlated with the physical properties (distribution, density, size, ...) of the dust grains in the coma.
In this work, a summary of the activities and main results obtained so far is presented, highlighting some original results obtained from METIS comet observations and sharing some valuable “lessons learned" from these four years of activity.
Acknowledgements
Solar Orbiter is a space mission of international collaboration between ESA and NASA, operated by ESA. Metis was built and operated with funding from the Italian Space Agency (ASI), under contracts to the National Institute of Astrophysics (INAF) and industrial partners. Metis was built with hardware contributions from Germany (Bundesministerium für Wirtschaft und Energie through DLR), from the Czech Republic (PRODEX) and from ESA.
References
[1] Antonucci et al, A&A 642, A10 (2020).
[2] Bemporad et al, A&A 680, A90 (2023).
[3] Corso et al, EPSC2022-901 (2022)
[4] Fineschi, S. et al., Exp. Astron. 49, 239-263 (2020).
How to cite: Corso, A. J., Da Deppo, V., Giordano, S., Nisticò, G., Bertini, I., Bemporad, A., Chioetto, P., and Romoli, M.: The Metis contribution in cometary science: an initial assessment of the first four years of activities, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1261, https://doi.org/10.5194/epsc2024-1261, 2024.
Comet Interceptor is the first Fast (F-class) mission in the European Space Agency (ESA) Cosmic Vision program and has been conceived to study a long-period comet. The mission concept includes a spin-stabilized probe venturing close to a yet-to-be selected, and possibly dynamically new, comet. On this probe, the Entire Visible Sky (EnVisS) camera will be hosted. EnVisS will address several fields of cometary science by carrying out observations, close to, and within, a comet’s coma. Both intensity and polarimetric measurements are foreseen. In this work, the up-to-date instrument concept, design and scientific capabilities of EnVisS will be presented.
1) Introduction
The Comet Interceptor spacecraft mission configuration includes a spacecraft (called A) and two probes (called PB1 and PB2). Spacecraft A will carry on remote and in-situ observations of the target from afar; while PB1, by the Japan Aerospace Space Agency (JAXA), and PB2, by ESA, will perform close fly-bys of the target [1].
PB2 spin-stabilized solution allows EnVisS to adopt a rotational push-broom or push-frame imaging technique to scan and image the whole environment around the probe. The filter strip assembly [2] mounted as close as possible to the detector grants the possibility to observe and perform polarimetric imaging in the visible range.
EnVisS will map the intensity and the degree of linear polarization and polarization angle orientation of the light scattered by the dust particles in the comet coma with an extended phase angle coverage. Linear polarization is directly linked with dust size distribution, morphology, porosity and composition [3]. Monitoring linear polarization will provide insights into how these parameters correlate.
2) Instrument concept
The EnVisS instrument works in the visible wavelength range from 550-800 nm. To acquire the full sky, it features an extremely wide Field of View (FoV).
EnVisS adopts a flexible push-broom/push-frame imaging technique: as the probe rotates (see Figure 1 ), slices of the sky are acquired and later stitched together on-ground to reconstruct a full-sky image.
Figure 1: In (a) placement of the EnVisS camera on the B2 probe. In (b) illustration of EnVisS full sky imaging scanning concept. In (c) schematics of the filter strips images on the 2k x 2k detector.
The probe spin-axis will point to the comet nucleus for most of the time, except at the closest approach when the comet nucleus will fall inside the camera FoV (see Figure 1 (a) for the EnVisS placement on PB2).
3) EnVisS: Instrument Design
The EnVisS instrument consists of different parts (see Figure 2 ):
- a fish-eye optical head [4];
- a commercial space-qualified detector package from 3D-Plus [5] equipped with an ad hoc filter strip package (FSA) [6];
- ad-hoc electronics (power and data handling units);
- software.
Figure 2: In (a) EnVisS CAD model. In (b) Optical head and camera components are highlighted [4].
The FSA contains three broad-band filters, all working in the same wavelength range (i.e., 550-800 nm):
- one broadband intensity filter centred on the detector (see Figure 1 (c) blue central strip I);
- two linear polarizing filters with transmission axis angles oriented at 45° one to the other; positioned on the sides (see Figure 1 (c) the red and yellow strips P1 and P2).
A flexible approach is considered to achieve the required SNR. Depending on the target object activity, the map of the coma will be taken with different spatial resolutions, i.e. smearing and pixel binning.
Along track, the signal from the coma is not expected to vary too much, high spatial resolution is not required and smearing can be tolerated. The spatial resolution is retained in the across-track direction and ensures a sampling of the comet phase function every 0.2°. This strategy will also allow for an adjustment of the exposure time if the radiance of the coma differs from expected.
Further pixel binning on-board, or co-adding, on-ground, of the images over different rotations, could be considered if the signal is extremely low.
Acknowledgements
This work has been supported by: the Italian Space Agency (ASI) through contracts to the Istituto Nazionale di Astrofisica (2020-4-HH and 2023-14-HH.0), and the European Space Agency (ESA) through a Contract to the Italian National Research Council (CNR) (Contract n. 4000136673/21/NL/IB/ig); and Instituto de Astrofísica de Andalucía (IAA-CSIC, Granada, Spain) with SENER (Barcelona, Spain) being supported by the Spanish Ministerio de Ciencia e Innovación (MCIN) through ESA PRODEX and the Spanish National Plan Ref PID2021-126365NB-C21 respectively.
References
[1] Jones, et al., “The Comet Interceptor Mission”, Space Sci Rev 220, 9 (2024).
[2] Naletto et al., “Characterization of the polarizing filters for the EnVisS camera”. Proc. SPIE paper 13092-225 (2024).
[3] Fulle, A.C. Levasseur-Regourd, N. McBride, E. Hadamcik "In situ dust measurements from within the coma of 1P/Halley, The Astronomical Journal, 119:1968-1977, (2000).
[4] Tofani, et al., “Design of the EnVisS instrument optical head”, SPIE Proc. 12777, International Conference on Space Optics — ICSO 2022; 127772P (2023).
[5] https://www.3d-plus.com/
[6] Nordera, et al., “Ghost analysis of the EnVisS camera for the Comet Interceptor ESA mission”, SPIE Proc. 12180, 1218036 (2022).
How to cite: Da Deppo, V., Della Corte, V., Zuppella, P., Lara, L. M., Castro, J. M., and Gutierrez, P. J. and the EnVisS Team: The Entire Visible Sky (EnVisS) instrument for the Comet Interceptor ESA mission: an update, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1307, https://doi.org/10.5194/epsc2024-1307, 2024.
Additional speaker
- Elena Martellato, INAF-OAPD, Italy