Cometary Science Newsletter
- Issue
- 106
- Month
- January 2024
- Editor
- Michael S. P. Kelley (msk@astro.umd.edu)
Refereed Articles
Abstracts of articles in press or recently published. Limited to 3000 characters.
The Return of the Rosetta Target: Keck Near-infrared Observations of Comet 67P/ Churyumov–Gerasimenko in 2021
- Department of Physics, American University, 4400 Massachusetts Avenue, NW, Washington, DC 20016, USA; bonev@american.edu
- Space Department, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
- Koyama Astronomical Observatory, Kyoto Sangyo University, Motoyama, Kita-ku, Kyoto 603-8555, Japan
- Solar System Exploration Division, Planetary Systems Laboratory, MS 693, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
- National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
- University of Occupational and Environmental Health Japan, Kitakyushu 807-8555, Japan
- Department of Physics and Astronomy, University of Missouri-St. Louis, Saint Louis, MO 63121, USA
- Department of Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA
- Physikalisches Institut, Universität Bern, Sidlerstr. 5, CH-3012 Bern, Switzerland
- LESIA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, 5 place Jules Janssen, F-92195 Meudon, France
- W. M. Keck Observatory, Kamuela, HI 96743, USA
- Physics Department, Auburn University, Auburn, AL 36832, USA
- Department of Physics and Astronomy, Appalachian State University, Boone, NC 28608-2106, USA
- McDonald Observatory, University of Texas at Austin, Austin, TX 78712, USA
- STAR Institute—University of Liège, Allée du 6 Août 19C, B-4000 Liège 1, Belgium
- Department of Physics, Catholic University of America, Washington, DC 20064, USA
- Solar System Exploration Division, Astrochemistry Laboratory Code 691, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA
High-resolution near-infrared ground-based spectroscopic observations of comet 67P/Churyumov–Gerasimenko near its maximum activity in 2021 were conducted from the W. M. Keck Observatory, using the facility spectrograph NIRSPEC. 67P is the best-studied comet to date because of the unprecedented detail and insights provided by the Rosetta mission during 2014–2016. Because 67P is the only comet where the detailed abundances of many coma volatiles were measured in situ, determining its composition from the ground provides a unique opportunity to interpret Rosetta results within the context of the large database of ground-based compositional measurements of comets. However, previous apparitions, including in 2015, have been unfavorable for in-depth ground-based studies of parent volatiles in 67P. The 2021 apparition of 67P was thus the first-ever opportunity for such observations. We report gas spatial distributions, rotational temperatures, production rates, and relative abundances (or stringent upper limits) among seven volatile species: C2H2, C2H6, HCN, NH3, CH3OH, H2CO, and H2O. The measured abundances of trace species relative to water reveal near average or below average values compared to previous comets studied at infrared wavelengths. Both gas rotational temperatures and the spatial distributions of H2O, C2H6, and HCN measured with Keck-NIRSPEC in 2021 are consistent with the outgassing patterns revealed by Rosetta in 2015 at very similar heliocentric distance (post-perihelion). These results can be integrated with both Rosetta mission findings and ground-based cometary studies of the overall comet population, for which we encourage a wide-scale collaboration across measurement techniques.
The Astronomical Journal (Published)
DOI: 10.3847/1538-3881/acee59 NASA ADS: 2023AJ....166..233B
Pits on Jupiter-family Comets and the Age of Cometary Surfaces
- LGL TPE, UMR 5276 CNRS, Université Lyon 1, ENS, Villeurbanne, France
- IRAP, UMR 5277 CNRS, Université de Toulouse 3, CNES, Toulouse, France
- European Space Agency (ESA), European Space Astronomy Centre (ESAC), Villanueva de la Cañada, Spain
- Aurora Technology B.V. for the European Space Agency, ESAC, Madrid, Spain
- Department of Physics, Imperial College London, Prince Consort Road, London SW7 2AZ, UK
Large and deep depressions, also known as pits, are observed at the surface of all Jupiter-family comets (JFCs) imaged by spacecraft missions. They offer the opportunity to glimpse the subsurface characteristics of comet nuclei and study the complex interplay between surface structures and cometary activity. This work investigates the evolution of pits at the surface of 81P/Wild 2, 9P/Tempel 1, and 103P/Hartley 2, in continuation of the work by Benseguane et al. on 67P/Churyumov-Gerasimenko. Pits are selected across the surface of each nucleus, and high-resolution shape models are used to compute the energy they receive. A thermal evolution model is applied to constrain how cometary activity sustained under current illumination conditions could modify them. Similar to what was found for 67P, we show that erosion resulting from water-driven activity is primarily controlled by seasonal patterns that are unique to each comet as a consequence of their shape and rotational properties. However, progressive erosion sustained after multiple perihelion passages is not able to carve any of the observed pits. Instead, cometary activity tends to erase sharp morphological features; they become wider and shallower over time. Our results reinforce the evolutionary sequence evidenced from independent measurables to transform "young" cometary surfaces, with sharp surface topography prone to outbursts, into "old" cometary surfaces. Finally, we suggest that the mechanism at the origin of the pits on JFCs should be able to carve these structures in a region of the solar system where water ice does not sublimate; the Centaur phase thus appears critical to understand JFC surface properties.
The Planetary Science Journal (Published)
DOI: 10.3847/PSJ/ad083a NASA ADS: 2023PSJ.....4..220G arXiv: 2311.02036