Cometary Science Newsletter

February 2018
Michael S. P. Kelley (

Conference Announcements

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

Observations of Planetary Objects with Non-Planetary Spacecraft (Session B0.3)

COSPAR 2018 - Pasadena, California, 14-22 July 2018
Abstracts due February 9th

Missions not primarily designed for planetary observations are nevertheless valuable sources of observational data on major, dwarf, and minor planets, as well as comets. Example missions are the NASA/ESA SOHO and NASA STEREO solar and heliospheric missions, that have returned observations of numerous comets, the NASA Kepler exoplanet mission which has observed planets and various small bodies, and ESA's Gaia mapping mission. In this session, we address such observations carried out by past and current missions as well as projects that are in development and proposed. Contributions are invited to provide an overview of results from such observations, and those planned for the future. Contributions that provide insights into the securing of serendipitous planetary observations to help advise future efforts are particularly encouraged.

Abstracts for contributed presentations at Session B0.3 are due on February 9, 2018, and must be submitted on the COSPAR website—full details for abstract submission, as well as the detailed description of the content of the session are available at

Organizers - Geraint Jones (MSSL, University College London, UK) & Matthew Knight (University of Maryland, USA)

Rosetta Workshop and SWT - Registration and abstract submission OPEN!

Dear Colleagues,

Please note that abstract submission and registration is now open for the Rosetta science extravaganza in Rhodes in May/June. Please go to the web page to register and if you like, submit an abstract.

Note that the special rate available at the conference hotel is only available up to March 26th. Please use the form available in the accommodation section of the conference web page to secure your room!

Registration fee is expected to be around 300 Euros and will include the conference dinner and excursion and for those staying in the conference hotel, this will also include lunch. Exact costs will be made clearer nearer the time, once we have a better idea at the number of participants.

Please pass this message on, the meeting is open to all scientists interested in comets, solar system formation and evolution, etc.

Best regards,

Matt Taylor, on behalf of the SOC

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.

Call for Observations of C/2016 R2 (PanSTARRS)

Recent observations at multiple wavelengths have revealed an atypical coma composition for comet C/2016 R2 (PanSTARRS), including very large CO production rates (Wierzchos and Womack, CBET4464) and the presence of N2+ and CO+ in the optical spectrum (Cochran and McKay, in press). We are working to obtain as many observations as possible at all wavelengths to fully characterize this comet, with observations already scheduled/obtained on facilities such as Spitzer, IRAM, SMT, and NASA IRTF. We encourage the cometary science community to observe this comet with any complementary or independent methods at their disposal. Of particular interest are data that can be obtained near simultaneously with scheduled observations with Spitzer on UT Feb 12 and Feb 21, though any observations obtained to date and over the next couple months will be beneficial. Please contact Adam McKay ( with any questions or to express interest.

JWST Cycle 1 Update: 88P/Howell and 313P/Gibbs

The James Webb Space Telescope's Guaranteed-Time Observation (GTO) program includes observations of comets in Heidi Hammel's "Solar System Observations with the James Web Space Telescope" GTO project. The targets were originally 46P/Wirtanen and a target of opportunity Oort cloud comet in Cycle 1, and main-belt comet 313P/Gibbs in Cycle 2. Given JWST's revised launch window of April - June 2019, the Space Telescope Science Institute approved replacing 46P/Wirtanen with 88P/Howell, and shifting 313P/Gibbs from Cycle 2 to Cycle 1. The target of opportunity comet project remains unchanged. These data will be made available to the planetary community immediately, in order to facilitate plans for future comet observations with Webb. See CSN Issue 20, or JWST proposals 1252 and 1253 for details.

Mike Kelley, Univ. Maryland
Stefanie Milam, NASA GSFC
Heidi Hammel, AURA

Refereed Articles

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

The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets

  • Geraint H. Jones 1, 2
  • Matthew M. Knight 3, 4
  • Karl Battams 5
  • Daniel C. Boice 6, 7, 8
  • John Brown 9
  • Silvio Giordano 10
  • John Raymond 11
  • Colin Snodgrass 12, 13
  • Jordan K. Steckloff 14, 15, 16
  • Paul Weissman 14
  • Alan Fitzsimmons 17
  • Carey Lisse 18
  • Cyrielle Opitom 19, 20
  • Kimberley S. Birkett 1, 2, 21
  • Maciej Bzowski 22
  • Alice Decock 19, 23
  • Ingrid Mann 24, 25
  • Yudish Ramanjooloo 1, 2, 26
  • Patrick McCauley 11
  1. Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, UK
  2. The Centre for Planetary Sciences at UCL/Birkbeck, London, UK
  3. University of Maryland, College Park, USA
  4. Lowell Observatory, Flagstaff, USA
  5. Naval Research Laboratory, Washington, D.C., USA
  6. Scientific Studies and Consulting, San Antonio, USA
  7. Trinity University, San Antonio, USA
  8. IAG, Universidade de São Paulo, São Paulo, Brasil
  9. University of Glasgow, Glasgow, UK
  10. Osservatorio Astrofisico di Torino, INAF, Pino Torinese, Italy
  11. Harvard-Smithsonian Center for Astrophysics, Cambridge, USA
  12. The Open University, Milton Keynes, UK
  13. Max Planck Institute for Solar System Research, Göttingen, Germany
  14. Planetary Science Institute, Tucson, USA
  15. Massachusetts Institute of Technology, Cambridge, USA
  16. Purdue University, West Lafayette, USA
  17. Queen’s University Belfast, Belfast, UK
  18. Johns Hopkins University Applied Physics Laboratory, Laurel, USA
  19. University of Liège, Liège, Belgium
  20. European Southern Observatory, Santiago de Chile, Chile
  21. Surrey Satellite Technology Ltd, Guildford, UK
  22. CBK, Warsaw, Poland
  23. Observatoire de Paris, Paris, France
  24. EISCAT Scientific Association, Kiruna, Sweden
  25. UiT The Arctic University of Norway, Tromsø, Norway
  26. Institute for Astronomy, University of Hawai’I, Honolulu, USA

This review addresses our current understanding of comets that venture close to the Sun, and are hence exposed to much more extreme conditions than comets that are typically studied from Earth. The extreme solar heating and plasma environments that these objects encounter change many aspects of their behaviour, thus yielding valuable information on both the comets themselves that complements other data we have on primitive solar system bodies, as well as on the near-solar environment which they traverse. We propose clear definitions for these comets: We use the term near-Sun comets to encompass all objects that pass sunward of the perihelion distance of planet Mercury (0.307 AU). Sunskirters are defined as objects that pass within 33 solar radii of the Sun’s centre, equal to half of Mercury’s perihelion distance, and the commonly-used phrase sungrazers to be objects that reach perihelion within 3.45 solar radii, i.e. the fluid Roche limit. Finally, comets with orbits that intersect the solar photosphere are termed sundivers. We summarize past studies of these objects, as well as the instruments and facilities used to study them, including space-based platforms that have led to a recent revolution in the quantity and quality of relevant observations. Relevant comet populations are described, including the Kreutz, Marsden, Kracht, and Meyer groups, near-Sun asteroids, and a brief discussion of their origins. The importance of light curves and the clues they provide on cometary composition are emphasized, together with what information has been gleaned about nucleus parameters, including the sizes and masses of objects and their families, and their tensile strengths. The physical processes occurring at these objects are considered in some detail, including the disruption of nuclei, sublimation, and ionisation, and we consider the mass, momentum, and energy loss of comets in the corona and those that venture to lower altitudes. The different components of comae and tails are described, including dust, neutral and ionised gases, their chemical reactions, and their contributions to the near-Sun environment. Comet-solar wind interactions are discussed, including the use of comets as probes of solar wind and coronal conditions in their vicinities. We address the relevance of work on comets near the Sun to similar objects orbiting other stars, and conclude with a discussion of future directions for the field and the planned ground- and space-based facilities that will allow us to address those science topics.

Open access article.

Space Science Reviews (Published)

DOI: 10.1007/s11214-017-0446-5

A rapid decrease in the rotation rate of comet 41P/Tuttle–Giacobini–Kresák

  • Bodewits D. 1
  • Farnham, T. 1
  • Kelley, M. S. P. 1
  • Knight, M. M. 1
  1. University of Maryland, College Park

Cometary outgassing can produce torques that change the spin state of the cometary nucleus, which in turn influences the evolution and lifetime of the comet. If these torques increase the rate of rotation to the extent that centripetal forces exceed the material strength of the nucleus, the comet can fragment. Torques that slow down the rotation can cause the spin state to become unstable, but if the torques persist the nucleus can eventually reorient itself and the rotation rate can increase again. Simulations predict that most comets go through a short phase of rapid changes in spin state, after which changes occur gradually over longer times. Here we report observations of comet 41P/Tuttle–Giacobini–Kresák during its close approach to Earth (0.142 astronomical units, approximately 21 million kilometres, on 1 April 2017) that reveal a rapid decrease in rotation rate. Between March and May 2017, the apparent rotation period of the nucleus increased from 20 hours to more than 46 hours—a rate of change of more than an order of magnitude larger than has hitherto been measured. This phenomenon must have been caused by the gas emission from the comet aligning in such a way that it produced an anomalously strong torque that slowed the spin rate of the nucleus. The behaviour of comet 41P/Tuttle–Giacobini– Kresák suggests that it is in a distinct evolutionary state and that its rotation may be approaching the point of instability.

Nature (Published)

DOI: 10.1038/nature25150 NASA ADS: 2018arXiv180103870B arXiv: 1801.03870