Cometary Science Newsletter

April 2023
Michael S. P. Kelley (

Refereed Articles

Abstracts of articles in press or recently published. Limited to 3000 characters.

Observational Characterization of Main-Belt Comet and Candidate Main-Belt Comet Nuclei

  • Hsieh, H. H. 1,2
  • Micheli, M. 3
  • Kelley, M. S. P. 4
  • Knight, M. M. 4,5
  • Moskovitz, N. A. 6
  • Pittichova, J. 7
  • Sheppard, S. S. 8
  • Thirouin, A. 6
  • Trujillo, C. A. 9
  • Wainscoat, R. J. 10
  • Weryk, R. J. 10,11
  • Ye, Q. 4,12
  1. Planetary Science Institute, USA
  2. Institute of Astronomy & Astrophysics, Academia Sinica, Taiwan
  3. ESA PDO NEO Coordination Centre, Italy;
  4. University of Maryland, USA
  5. US Naval Academy, USA
  6. Lowell Observatory, USA
  7. Jet Propulsion Laboratory, USA
  8. Carnegie Institution for Science, USA
  9. Northern Arizona University, USA
  10. University of Hawaii, USA
  11. University of Western Ontario, Canada
  12. Boston University, USA

We report observations of nine main-belt comets (MBCs) or candidate MBCs, most of which were obtained when the targets were apparently inactive. We find effective nucleus radii (assuming albedos of pV=0.05±0.02 of rn=(0.24±0.05) km for 238P/Read, rn=(0.9±0.2) km for 313P/Gibbs, rn=(0.6±0.1) km for 324P/La Sagra, rn=(1.0±0.2) km for 426P/PANSTARRS, rn=(0.5±0.1) km for 427P/ATLAS, rn<(0.3±0.1) km for P/2016 J1-A (PANSTARRS), rn<(0.17±0.04) km for P/2016 J1-B (PANSTARRS), rn<(0.5±0.2) km for P/2017 S9 (PANSTARRS), and rn=(0.4±0.1) km for P/2019 A3 (PANSTARRS). We identify evidence of activity in observations of 238P in 2021, and find similar inferred activity onset times and net initial mass loss rates for 238P during perihelion approaches in 2010, 2016, and 2021. P/2016 J1-A and P/2016 J1-B are also found to be active in 2021 and 2022, making them collectively the tenth MBC confirmed to be recurrently active near perihelion and therefore likely to be exhibiting sublimation-driven activity. The nucleus of 313P is found to have colors of g'-r'=0.52±0.05 and r'-i'=0.22±0.07, consistent with 313P being a Lixiaohua family member. We also report non-detections of P/2015 X6 (PANSTARRS), where we conclude that its current nucleus size is likely below our detection limits (rn<0.3 km). Lastly, we find that of 17 MBCs or candidate MBCs for which nucleus sizes (or inferred parent body sizes) have been estimated, >80% have rn<1.0 km, pointing to an apparent physical preference toward small MBCs, where we suggest that YORP spin-up may play a significant role in triggering and/or facilitating MBC activity.

The Planetary Science Journal (Published)

DOI: 10.3847/PSJ/acbdfe NASA ADS: 2023PSJ.....4...43H arXiv: 2302.11689

Evolution of pits at the surface of 67P/Churyumov-Gerasimenko

  • Selma Benseguane 1
  • Aurélie Guilbert-Lepoutre 1
  • Jérémie Lasue 2
  • Sébastien Besse 3
  • Cédric Leyrat 4
  • Arnaud Beth 5
  • Marc Costa Sitjà 6
  • Björn Grieger 3
  • Maria Teresa Capria 7
  1. LGL-TPE, CNRS, Université Lyon, UCBL, ENSL, 69622 Villeurbanne, France
  2. IRAP, Université de Toulouse, CNRS, CNES, UPS, 31400 Toulouse, France
  3. Aurora Technology B.V. for the European Space Agency, ESAC, 28692 Villanueva de la Canada, Madrid, Spain
  4. LESIA, Observatoire de Paris, CNRS, Sorbonne Univ., Univ. Paris-Diderot, Meudon, France
  5. Department of Physics, Umeå University, 901 87 Umeå , Sweden
  6. Rhea System for the European Space Agency, ESAC, 28692 Villanueva de la Canada, Madrid, Spain
  7. Istituto di Astrofisica e Planetologia Spaziali (IAPS), INAF, 00133 Roma, Italy

Context. The observation of pits at the surface of comets offers the opportunity to take a glimpse into the properties and the mechanisms that shape a nucleus through cometary activity. If the origin of these pits is still a matter of debate, multiple studies have recently suggested that known phase transitions (such as volatile sublimation or amorphous water ice crystallization) alone could not have carved these morphological features on the surface of 67P/Churyumov-Gerasimenko (hereafter 67P).

Aims. We want to understand how the progressive modification of 67P’s surface due to cometary activity might have affected the characteristics of pits and alcoves. In particular, we aim to understand whether signatures of the formation mechanism of these surface morphological features can still be identified.

Methods. To quantify the amount of erosion sustained at the surface of 67P since it arrived on its currently observed orbit, we selected 380 facets of a medium-resolution shape model of the nucleus, sampling 30 pits and alcoves across the surface. We computed the surface energy balance with a high temporal resolution, including shadowing and self-heating contributions. We then applied a thermal evolution model to assess the amount of erosion sustained after ten orbital revolutions under current illumination conditions.

Results. We find that the maximum erosion sustained after ten orbital revolutions is on the order of 80 m, for facets located in the southern hemisphere. We thus confirm that progressive erosion cannot form pits and alcoves, as local erosion is much lower than their observed depth and diameter. We find that plateaus tend to erode more than bottoms, especially for the deepest depressions, and that some differential erosion can affect their morphology. As a general rule, our results suggest that sharp morphological features tend to be erased by progressive erosion.

Conclusions. This study supports the assumption that deep circular pits, such as Seth_01, are the least processed morphological features at the surface of 67P, or the best preserved since their formation.

Astronomy & Astrophysics (Published)

DOI: 10.1051/0004-6361/202243983 NASA ADS: 2022A&A...668A.132B arXiv: 2210.14634

Cometary dust collected by MIDAS on board Rosetta. I. Dust particle catalog and statistics

  • Kim, M. 1,2,3
  • Mannel, T. 1
  • Boakes, P. D. 1
  • Bentley, M. S. 4
  • Longobardo, A. 5
  • Jeszenszky, H. 1
  • Moissl, R. 6
  • and the MIDAS team
  1. Space Research Institute of the Austrian Academy of Sciences, Schmiedlstrasse 6, 8042 Graz, Austria
  2. Department of Physics, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
  3. Centre for Exoplanets and Habitability, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
  4. European Space Astronomy Centre, Camino Bajo del Castillo, s/n., Urb. Villafranca del Castillo, 28692 Villanueva de la Cañada, Madrid, Spain
  5. Istituto Nazionale di Astrofisica, Istituto di Astrofisica e Planetologia Spaziali, via Fosso del Cavaliere 100, I-00133 Rome, Italy
  6. Scientific Support Office, Directorate of Science, European Space Research and Technology Centre, 2201 AZ Noordwijk, The Netherlands

We aim to catalog all dust particles collected and analyzed by MIDAS, together with their main statistical properties such as size, height, basic shape descriptors, and collection time. Furthermore, we aim to present the scientific results that can be extracted from the catalog (e.g., the size distribution and statistical characteristics of cometary dust particles). The existing MIDAS particle catalog has been greatly improved by a careful re-analysis of the AFM images, leading to the addition of more dust particles and a detailed description of the particle properties. The catalog documents all images of identified dust particles and includes a variety of derived information tabulated one record per particle. Furthermore, the best image of each particle was chosen for subsequent studies. Finally, we created dust coverage maps and clustering maps of the MIDAS collection targets and traced any possible fragmentation of collected particles with a detailed algorithm. The revised MIDAS catalog includes 3523 MIDAS particles in total, where 1857 particles are expected to be usable for further analysis (418 scans of particles before perihelion + 1439 scans of particles after perihelion, both after the removal of duplicates), ranging from about 40 nm to about 8 μm in size. The mean value of the equivalent radius derived from the 2D projection of the particles is 0.91 ± 0.79 μm. A slightly improved equivalent radius based on the particle's volume coincides in the range of uncertainties with a value of 0.56 ± 0.45 μm. We note that those sizes and all following MIDAS particle size distributions are expected to be influenced by the fragmentation of MIDAS particles upon impact on the collection targets. Furthermore, fitting the slope of the MIDAS particle size distribution with a power law of a r^b yields an index b of ~ -1.67 to -1.88.

Astronomy & Astrophysics (In press)

DOI: 10.48550/arXiv.2302.10721 NASA ADS: 2023arXiv230210721K arXiv: 2302.10721