Cometary Science Newsletter

June 2019
Michael S. P. Kelley (

Conference Announcements

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

Announcement of an archive splinter on Rosetta data at the AOGS meeting

Dear colleagues,

The AOGS meeting will be held 28 July to 2 August in Singapore. For those attending, we would like to bring the following open session to your attention: WS02 Rosetta Mission Data on Tuesday 30 July from 4- 6 PM.

The aim of the session, open to all, is to provide a quick insight into the Rosetta Mission data available at ESA's Planetary Science Archive. The session will include a short presentation of the ESA Planetary Science Archive as a whole and on the Rosetta archive in particular. This will be followed by presentations from a few instrument teams who will give a brief overview of their archive data, to provide instrument level insights into data access, as well as tips on how to best use the Rosetta data. If time permits we hope to include some hands on activities. The goal of the session is to make the attendees as autonomous as possible with Rosetta data, to encourage wider use of this scientifically treasure chest, so that the attendees can quickly start carrying out their own cometary science studies.

The session will be convened by Dave Heather, archive specialist from ESA and Pierre Henri, PI of the RPC-MIP instrument on Rosetta. Different representatives of various PI instrument teams will be present.

Warm regards
Matt Taylor, Dave Heather and Pierre Henri

New Cometary Insights from the Close Approach of 46P/Wirtanen: A Symposium in Celebration of Mike A'Hearn

Registration for the meeting, which will be held August 6-8, 2019 on the University of Maryland campus is now open.

For more information about the meeting and a link to the registration site, go to

Refereed Articles

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

Properties of the Bare Nucleus of Comet 96P/Machholz 1

  • Eisner, N.E. 1,2
  • Knight, M.M. 1
  • Snodgrass, C. 3,4
  • Kelley, M.S.P. 1
  • Fitzsimmons, A. 5
  • Kokotanekova, R. 4,6,7
  1. University of Maryland, USA
  2. University of Oxford, UK
  3. University of Edinburgh, UK
  4. The Open University, UK
  5. Queen's University Belfast, UK
  6. European Southern Observatory, Germany
  7. Max-Planck-Institut für Sonnensystemforschung, Germany

We observed comet 96P/Machholz 1 on a total of nine nights before and after perihelion during its 2017/2018 apparition. Both its unusually small perihelion distance and the observed fragmentation during multiple apparitions make 96P an object of great interest. Our observations show no evidence of a detectable dust coma, implying that we are observing a bare nucleus at distances ranging from 2.3 to 3.8 au. Based on this assumption, we calculated its color and found average values of g'–r' = 0.50 ± 0.04, r'–i' = 0.17 ± 0.03, and i'–z' = 0.06 ± 0.04. These are notably more blue than those of the nuclei of other Jupiter-family and long-period comets. Furthermore, assuming a bare nucleus, we found an equivalent nuclear radius of 3.4 ± 0.2 km with an axial ratio of at least 1.6 ± 0.1. The lightcurve clearly displays one large peak, one broad flat peak, and two distinct troughs, with a clear asymmetry that suggests that the shape of the nucleus deviates from that of a simple triaxial ellipsoid. This asymmetry in the lightcurve allowed us to constrain the nuclear rotation period to 4.10 ± 0.03 hr and 4.096 ± 0.002 hr before and after perihelion, respectively. Within the uncertainties, 96P’s rotation period does not appear to have changed throughout the apparition, and we conclude a maximum possible change in rotation period of 130 s. The observed properties were compared to those of comet 322P and interstellar object 1I/‘Oumuamua in an attempt to study the effects of close perihelion passages on cometary surfaces and their internal structure and the potential interstellar origin of 96P.

Astronomical Journal (Published)

DOI: 10.3847/1538-3881/ab0f42 NASA ADS: 2019AJ....157..186E arXiv: 1903.10500