Cometary Science Newsletter

October 2019
Michael S. P. Kelley (

Conference Announcements

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

Astrochemical Complexity in Planetary Systems

This symposium will be held at the 259th ACS National Meeting, Philadelphia, PA, 22-26 March 2020.

The aim is to bring together laboratory, theoretical and observational astrochemists with planetary scientists to generate insights into the origins of chemical complexity in planetary systems.

Session Topics:

  1. Chemical Complexity from the ISM to Disks: Observations and Models.
  2. Experimental and Theoretical Techniques for Interstellar/Planetary Chemistry.
  3. The Outer Solar System, Comets, Icy Rings, and Satellites.
  4. Inner Solar System, Asteroids and Giant Planets.
  5. Organics in Meteorites.
  6. Organics on the Primordial Earth.
  7. Emerging Techniques for Sample Analysis.

Confirmed Invited Speakers: Brett McGuire, Jennifer Bergner, Susanna Widicus Weaver, Hervé Cottin, Chao He, Kathrin Altwegg, Hunter Waite, Yoko Kebukawa, Jay Forsythe, Mehmet Yesiltas, Amanda Hendrix, Jamie Elsila, Ryan Fortenberry, Reggie Hudson, Mike McCarthy, Steven Charnley, Scott Sandford.

Visit to submit a talk or poster abstract (deadline is 2019 October 14th). For additional details see

Dr M. Cordiner and Dr. C. Bennett
Symposium organizers

Comet Notes

Brief observational reports or other notes related to specific comets. Limited to 1000 characters. The CSN is not intended to replace telegram services or other breaking news outlets.

Microphysics of Dust in the Interstellar Comet C/2019 Q4 (Borisov)

We retrieve chemical composition and size distribution of dust in the interstellar comet C/2019 Q4 (Borisov) based on its color slope in the visible. We find that the coma unlikely consists of the water-ice particles, Mg-rich silicate particles, or amorphous-carbon particles. Instead, its color slope is consistent with either Mg-Fe silicate particles or organics particles. However, color slope is known to be a subject of fast and significant variations in comets. Therefore, further monitoring of color in comet Borisov is highly desirable.

The short report of this study has been published in the Research Notes of the AAS, Vol. 3, Iss. 9, article ID 138:

Refereed Articles

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

Disintegrating In-Bound Long-Period Comet C/2019 J2

  • Jewitt, D. 1
  • Luu, J. 2
  1. UCLA
  2. Draper Laboratory

We present observations of the disintegrating long-period comet C/2019 J2 (Palomar) taken to determine the nature of the object and the cause of its demise. The data are consistent with break-up of a sub-kilometer nucleus into a debris cloud of mass about 1e9 kg, peaking on UT 2019 May 24+/-12. This is two months before perihelion and at a heliocentric distance of 1.9 AU. We consider potential mechanisms of disintegration. Tidal disruption is ruled-out, because the comet has not passed within the Roche sphere of any planet. Impact disruption is implausible, because the comet orbit is highly inclined (inclination 105.1 deg) and disruption occurred far above the ecliptic, where asteroids are rare. The back-pressure generated by sublimation (0.02 to 0.4 N/m2) is orders of magnitude smaller than the reported compressive strength (30 to 150 N/m2) of cometary material and, therefore, is of no importance. The depletion of volatiles by sublimation occurs too slowly to render the nucleus inactive on the timescale of infall. However, we find that the e-folding timescale for spin-up of the nucleus by the action of sublimation torques is shorter than the infall time, provided the nucleus radius is < 0.4 km. Thus, the disintegration of C/2019 J2 is tentatively interpreted as the rotational disruption of a sub-kilometer nucleus caused by outgassing torques.

The Astrophysical Journal Letters (Published)

DOI: 10.3847/2041-8213/ab4135 NASA ADS: 2019ApJ...883L..28J arXiv: 1909.01964

Cometary compositions compared with protoplanetary disk midplane chemical evolution. An emerging chemical evolution taxonomy for comets.

  • Eistrup, C 1,2
  • Walsh, C 3
  • van Dishoeck, E. F. 1,4
  1. Leiden Observatory, Netherlands
  2. Department of Astronomy, University of Virginia, USA and Virginia Initiative on Cosmic Origins Fellow
  3. School of Physics and Astronomy, University of Leeds, UK
  4. Max-Planck-Institut für Extraterrestriche Physik, Garching, Germany

[Abridged] With a growing number of molecules observed in many comets, and an improved understanding of chemical evolution in protoplanetary disk midplanes, comparisons can be made between models and observations that could potentially constrain the formation histories of comets. A χ2-method was used to determine maximum likelihood surfaces for 14 different comets that formed at a given time (up to 8 Myr) and place (out to beyond the CO iceline) in the pre-solar nebula midplane. This was done using observed volatile abundances for the 14 comets and the evolution of volatile abundances from chemical modelling of disk midplanes. Considering all parent species (ten molecules) in a scenario that assumed reset initial chemistry, the χ2 likelihood surfaces show a characteristic trail in the parameter space with high likelihood of formation around 30 AU at early times and 12 AU at later times for ten comets. This trail roughly traces the vicinity of the CO iceline in time. The formation histories for all comets were thereby constrained to the vicinity of the CO iceline, assuming that the chemistry was partially reset early in the pre-solar nebula. This is found, both when considering carbon-, oxygen-, and sulphur-bearing molecules (ten in total), and when only considering carbon- and oxygen-bearing molecules (seven in total). Since these 14 comets did not previously fall into the same taxonomical categories together, this chemical constraint may be proposed as an alternative taxonomy for comets. Based on the most likely time for each of these comets to have formed during the disk chemical evolution, a formation time classification for the 14 comets is suggested.

Astronomy & Astrophysics (Published)

DOI: 10.1051/0004-6361/201935812 NASA ADS: 2019A&A...629A..84E arXiv: 1907.11255