Cometary Science Newsletter

February 2023
Michael S. P. Kelley (

Conference Announcements

Announcements for cometary conferences or workshops. Limited to 2000 characters.

Active small bodies in the Solar System over a wide range of heliocentric distances

The workshop will provide a cross-disciplinary knowledge exchange on the physics of the small bodies in the Solar system revealing a comet-like activity, new space missions (Comet Interceptor, Destinity+, Lucy), and related ground-based observational campaigns.

The workshop will take place in Stará Lesná, Slovakia from 5th – 8th September 2023.

The meeting is open for every active small bodies fan, though the number of participants is limited. Contributions will be carefully selected by the SOC.

The workshop is organized by the Astronomical Institute of Slovak Academy of Sciences in Tatranská Lomnica.

Refereed Articles

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

Disintegration of Long-Period Comet C/2021 A1 (Leonard)

  • Jewitt, D. 1
  • Kim, Y. 2
  • Mattiazzo, M. 3
  • Mutchler, M. 4
  • Li, J. 1
  • Agarwal, J. 2
  1. UCLA
  2. TU Braunschweig
  3. Swan Hill Observatory
  4. STSCI

We present imaging observations of the disintegrating long-period comet C/2021 A1 (Leonard). High resolution observations with Hubble Space Telescope show no evidence for surviving fragments, and place a 3σ upper limit to their possible radius about 60 m (albedo 0.1 assumed). In contrast, wide field observations from the Swan Hill Observatory, Australia, show an extensive debris cloud, the cross-section and estimated mass of which are consistent with complete disintegration of the nucleus near mid- December 2021 (at about 0.8 au). Two methods give the pre-disruption nucleus radius, r = 0.6 ± 0.2 km. Tidal, collisional, sublimation and pressure-confined explosion models provide implausible explanations of the disintegration. However, rotational instability driven by outgassing torques has a very short timescale (about 0.1 year) given the orbit and size of the C/2021 A1 nucleus, and offers the most plausible mechanism for the disruption. Initial rotational breakup is accelerated by the exposure and strong sublimation of previously buried volatiles, leading to catastrophic destruction of the nucleus.

The Astronomical Journal (In press)

arXiv: 2301.08673

Strongly Depleted Methanol and Hypervolatiles in Comet C/2021 A1 (Leonard): Signatures of Interstellar Chemistry?

  • Sara Faggi 1,2
  • Manuela Lippi 3
  • Michael J. Mumma 2,4
  • Geronimo L. Villanueva 2
  1. American University, 4400 Massachusetts Avenue NW, Washington, DC 20016, USA;
  2. NASA Goddard Space Flight Center, 8800 Greenbelt Road, MD 20771, USA
  3. Institute for Geophysics and Extraterrestrial Physics, Technische Universität Braunschweig, Mendelssohnstraße 3, D-38106 Braunschweig, Germany
  4. University of Maryland, 1940 Regents Drive, College Park, MD 20740, USA
We measured the chemical composition of comet C/2021 A1 (Leonard) using the long-slit echelle grating spectrograph iSHELL/IRTF on 2021 December 20 and on 2022 January 8 and 9. We sampled 11 primary volatiles (H2O, HCN, NH3, CO, C2H2, C2H6, CH4, CH3OH, H2CO, OCS, and HCl) and three product species (CN, NH2, and OH) and retrieved their molecular abundances, which can serve as important cosmogonic indicators. The abundance ratios, relative to water, of almost all trace volatiles appear to be depleted relative to reference values, with methanol abundance among the lowest observed in a comet. The observed stronger depletion of CH3OH, relative to CO, CH4, and C2H6, could be evidence of an interstellar medium (ISM) chemistry signature in comet/ Leonard ices. Both the detection of HCl and the detection of OCS support the idea of interstellar origin for comet/ Leonard ices, since they are preferentially formed via solid-phase interstellar chemistry and are then found depleted in dense molecular clouds and protoplanetary disks, suggesting that their abundances in comets might retain a signature from the ISM era. The comet also revealed a complex outgassing pattern, with volatiles largely shifted toward the sunward direction, relative to the dust profiles that appeared centered on the nucleus-centric position. Here we present emission profiles measured along the Sun–comet line for brightest lines of H2O, HCN, C2H6, and CO, and we show that they follow the release of water in similar fashion, interpreting this as indication of a not strict relationship between polar and apolar ices.

The Planetary Science Journal (Published)

DOI: 10.3847/PSJ/aca64c