Cometary Science Newsletter

Issue
86
Month
May 2022
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

Refereed Articles

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

A SUBLIME 3D Model for Cometary Coma Emission: the Hypervolatile-Rich Comet C/2016 R2 (PanSTARRS)

  • M. A. Cordiner 1,2
  • I. M. Coulson 3
  • E. Garcia-Berrios 1,2
  • C. Qi 4
  • F. Lique 5
  • M. Zoltowski 5
  • and 9 co-authors
  1. Astrochemistry Laboratory, NASA Goddard Space Flight Center, 8800 Greenbelt Road, Greenbelt, MD 20771, USA.
  2. Department of Physics, Catholic University of America, Washington, DC 20064, USA.
  3. East Asian Observatory, 660 N. A’ohoku Place, Hilo, HI 96720, USA.
  4. Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, MS 42, Cambridge, MA 02138, USA.
  5. Université de Rennes 1, Campus de Beaulieu, 263 avenue du General Leclerc, 35042 Rennes Cedex, France.

The coma of comet C/2016 R2 (PanSTARRS) is one of the most chemically peculiar ever observed, in particular due to its extremely high CO/H2O and N2+/H2O ratios, and unusual trace volatile abundances. However, the complex shape of its CO emission lines, as well as uncertainties in the coma structure and excitation, has lead to ambiguities in the total CO production rate. We performed high resolution, spatially, spectrally and temporally resolved CO observations using the James Clerk Maxwell Telescope (JCMT) and Submillimeter Array (SMA) to elucidate the outgassing behavior of C/2016 R2. Results are analyzed using a new, time-dependent, three dimensional radiative transfer code (SUBlimating gases in LIME; SUBLIME, based on the open-source version of the LIne Modeling Engine), incorporating for the first time, accurate state-to-state collisional rate coefficients for the CO−CO system. The total CO production rate was found to be in the range (3.8−7.6)×10^28 s^−1 between 2018-01-13 and 2018-02-01, with a mean value of (5.3±0.6)×10^28 s^−1 at r_H = 2.8−2.9 au. The emission is concentrated in a near-sunward jet, with a half-opening angle of ~62 degrees and an outflow velocity 0.51±0.01 km/s, compared to 0.25±0.01 km/s in the ambient (and night-side) coma. Evidence was also found for an extended source of CO emission, possibly due to icy grain sublimation around 1.2×10^5 km from the nucleus. Based on the coma molecular abundances, we propose that the nucleus ices of C/2016 R2 can be divided into a rapidly sublimating apolar phase, rich in CO, CO2, N2 and CH3OH, and a predominantly frozen (or less abundant), polar phase containing more H2O, CH4, H2CO and HCN.

The Astrophysical Journal (Published)

DOI: 10.3847/1538-4357/ac5893 arXiv: 2202.11849

Thermal Processing of Jupiter-family Comets during Their Chaotic Orbital Evolution

  • Gkotsinas, A. 1
  • Guilbert-Lepoutre, A. 1
  • Raymond, S.N. 2
  • Nesvorny, D. 3
  1. Laboratoire de Géologie de Lyon : Terre, Planètes, Environnnement, CNRS, UCBL, ENSL, F-69622, Villeurbanne, France
  2. Laboratoire d'Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, F-33615 Pessac, France
  3. Department of Space Studies, Southwest Research Institute, 1050 Walnut Street, Suite 300, Boulder, CO 80302, USA

Evidence for cometary activity beyond Jupiter and Saturn's orbits – such as that observed for Centaurs and long period comets – suggests that the thermal processing of comet nuclei starts long before they enter the inner Solar System, where they are typically observed and monitored. Such observations raise questions as to the depth of unprocessed material, and whether the activity of JFCs can be representative of any primitive material. Here we model the coupled thermal and dynamical evolution of Jupiter Family Comets (JFCs), from the moment they leave their outer Solar System reservoirs until their ejection into interstellar space. We apply a thermal evolution model to a sample of simulated JFCs obtained from dynamical simulations (arXiv:1706.07447) that successfully reproduce the orbital distribution of observed JFCs. We show that due to the stochastic nature of comet trajectories toward the inner solar system, all simulated JFCs undergo multiple heating episodes resulting in significant modifications of their initial volatile contents. A statistical analysis constrains the extent of such processing. We suggest that primordial condensed hypervolatile ices should be entirely lost from the layers that contribute to cometary activity observed today. Our results demonstrate that understanding the orbital (and thus, heating) history of JFCs is essential when putting observations in a broader context.

The Astrophysical Journal (Published)

DOI: 10.3847/1538-4357/ac54ac NASA ADS: 2022ApJ...928...43G arXiv: 2202.06685