Cometary Science Newsletter

April 2018
Michael S. P. Kelley (

LSST Solar System Science Collaboration Science Roadmap

Megan E. Schwamb, R. Lynne Jones, Steven R. Chesley, Alan Fitzsimmons, Wesley C. Fraser, Matthew J. Holman, Henry Hsieh, Darin Ragozzine, Cristina A. Thomas, David E. Trilling, Michael E. Brown, Michele T. Bannister, Dennis Bodewits, Miguel de Val-Borro, David Gerdes, Mikael Granvik, Michael S. P. Kelley, Matthew M. Knight, Robert L. Seaman, Quan-Zhi Ye, Leslie A. Young

The Large Synoptic Survey Telescope (LSST) is uniquely equipped to search for Solar System bodies due to its unprecedented combination of depth and wide field coverage. Over a ten-year period starting in 2022, LSST will generate the largest catalog of Solar System objects to date. The main goal of the LSST Solar System Science Collaboration (SSSC) is to facilitate the efforts of the planetary community to study the planets and small body populations residing within our Solar System using LSST data. To prepare for future survey cadence decisions and ensure that interesting and novel Solar System science is achievable with LSST, the SSSC has identified and prioritized key Solar System research areas for investigation with LSST in this roadmap. The ranked science priorities highlighted in this living document will inform LSST survey cadence decisions and aid in identifying software tools and pipelines needed to be developed by the planetary community as added value products and resources before the planned start of LSST science operations.

Postdoctoral Position on Main Belt Comets at MPS, Germany

The Max Planck Institute for Solar System Research in Göttingen, Germany, invites applications for a postdoctoral position to work on the active binary asteroid (Main Belt Comet) 288P/300163.

Details are found at

Conference Announcements

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

Physics of Comets After the Rosetta Mission: Unresolved Problems

Dear Colleagues,

We invite You to register and submit an abstract of your contribution to the workshop “Physics of comets after the Rosetta mission: Unresolved problems” (September 5-7, 2018). The workshop will take place in Stará Lesná (Vysoké Tatry), Slovakia. The workshop will gather researchers studying different aspects of the physics of comets and discuss about the heritage of the Rosetta mission with special emphasis on the remaining issues, unresolved problems, and unexpected findings. Special attention also will be paid to the interrelation of the Rosetta findings at Comet 67P/Churyumov–Gerasimenko with results obtained in other comets in situ as well as in ground-based and space-born astronomical observations. Another important aspect of the workshop will be to examine disagreements between Rosetta findings and predictions of existing theoretical models, numerical simulations, and/or laboratory experiments. If you believe Rosetta has raised more questions than it has provided answers, you are very welcome at the workshop.

The planned registration and abstract submission deadline is April 30, 2018. More information can be found on the workshop website:

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.

Comet Wirtanen Campaign

The Wirtanen Campaign is starting to heat up. Comet 46P/Wirtanen should be recoverable soon, signaling the start of the 2018 observing season leading up to its close approach in December.

While we are waiting for Wirtanen to appear, I am making some changes and additions to the Campaign website. Expect these changes in the next few days:

  1. Individual pages for some other upcoming bright comets (think of them as practice targets): 21P/Giacobini-Zinner and 64P/Swift-Gehrels.
  2. A new page that includes a number of other comets that are of interest, but don't necessarily require a separate web page.
  3. Text tidbits that can be included as justifications in observing proposals for comet Wirtanen.

You can access the website at

Refereed Articles

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

Orbital Alignment of Main-Belt Comets

  • Yoonyoung Kim 1
  • Youngmin JeongAhn 2,3
  • Henry H. Hsieh 4,5
  1. Seoul National University, Korea
  2. Korea Astronomy and Space Science Institute, Korea
  3. Universidad Nacional Autónoma de México, México
  4. Planetary Science Institute, USA
  5. Academia Sinica, Taiwan

We examine the orbital element distribution of main-belt comets (MBCs), which are objects that exhibit cometary activity yet orbit in the main asteroid belt, and may be potentially useful as tracers of ice in the inner solar system. We find that the currently known and currently active MBCs have remarkably similar longitudes of perihelion, which are also aligned with that of Jupiter. The clustered objects have significantly higher current osculating eccentricities relative to their proper eccentricities, consistent with their orbits being currently, though only temporarily, secularly excited in osculating eccentricity due to Jupiter's influence. At the moment, most MBCs seem to have current osculating elements that may be particularly favorable for the object becoming active (e.g., maybe because of higher perihelion temperatures or higher impact velocities causing an effective increase in the size of the potential triggering impactor population). At other times, other icy asteroids will have those favorable conditions and might become MBCs at those times as well.

The Astronomical Journal (In press)

NASA ADS: 2018arXiv180200566K arXiv: 1802.00566

Evolution of Cometary Dust Particles to the Orbit of the Earth: Particle Size, Shape, and Mutual Collisions

  • Yang, H. 1,2
  • Ishiguro, M. 1
  1. Department of Physics and Astronomy, Seoul National University, 599 Gwanak-ro, Gwanak-gu, Seoul 151-742, Republic of Korea
  2. Korea Astronomy and Space Science Institute (KASI), Republic of Korea

In this study, we numerically investigated the orbital evolution of cometary dust particles, with special consideration of the initial size–frequency distribution (SFD) and different evolutionary tracks according to the initial orbit and particle shape. We found that close encounters with planets (mostly Jupiter) are the dominating factor determining the orbital evolution of dust particles. Therefore, the lifetimes of cometary dust particles (∼250,000 yr) are shorter than the Poynting–Robertson lifetime, and only a small fraction of large cometary dust particles can be transferred into orbits with small semimajor axis. The exceptions are dust particles from 2P/Encke and, potentially, active asteroids that have little interaction with Jupiter. We also found that the effects of dust shape, mass density, and SFD were not critical in the total mass supply rate to the interplanetary dust particle (IDP) cloud complex when these quantities are confined by observations of zodiacal light brightness and SFD around the Earth’s orbit. When we incorporate a population of fluffy aggregates discovered in the Earth’s stratosphere and the coma of 67P/Churyumov–Gerasimenko within the initial ejection, the initial SFD measured at the comae of comets (67P and 81P/Wild 2) can produce the observed SFD around the Earth’s orbit. Considering the above effects, we derived the probability of mutual collisions among dust particles within the IDP cloud for the first time in a direct manner via numerical simulation and concluded that mutual collisions can mostly be ignored.

The Astrophysical Journal (In press)

arXiv: 1801.09332

Evolution of H2O Production in Comet C/2012 S1 (ISON) as Inferred from Forbidden Oxygen and OH Emission

  • McKay, A.J 1
  • Cochran, A.L. 2
  • DiSanti, M.A. 3
  • Dello Russo, N. 4
  • Weaver, H. 4
  • Vervack, R.J. Jr. 4
  • Harris, W.M. 5
  • Kawakita, H. 6
  1. NASA GSFC/USRA, Greenbelt, MD
  2. University of Texas at Austin/McDonald Observatory, Austin, TX
  3. NASA GSFC, Greenbelt, MD
  4. Johns Hopkins Applied Physics Laboratory, Laurel, MD
  5. Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ
  6. Kyoto Sangyo University, Kyoto, Japan

We present H2O production rates for comet C/2012 S1 (ISON) derived from observations of [O I] and OH emission during its inbound leg, covering a heliocentric distance range of 1.8-0.44 AU. Our production rates are in agreement with previous measurements using a variety of instruments and techniques and with data from the various observatories greatly differing in their projected fields of view. The consistent results across all data suggest the absence of an extended source of H2O production, for example sublimation of icy grains in the coma, or a source with spatial extent confined to the dimensions of the smallest projected field of view (in this case  <  1,000 km). We find that ISON had an active area of around 10 km2 for heliocentric distances Rh  >  1.2 AU, which then decreased to about half this value from Rh=1.2-0.9 AU. This was followed by a rapid increase in active area at about Rh=0.6 AU, corresponding to the first of three major outbursts ISON experienced inside of 1 AU. The combination of a detected outburst in the light curve and rapid increase in active area likely indicates a major nucleus fragmentation event. The 5-10 km2 active area observed outside of Rh=0.6 AU is consistent with a 50-100% active fraction for the nucleus, larger than typically observed for cometary nuclei. Although the absolute value of the active area is somewhat dependent on the thermal model employed, the changes in active area observed are consistent among models. The conclusion of a 50-100+% active fraction is robust for realistic thermal models of the nucleus. However the possibility of a contribution of a spatially unresolved distribution of icy grains cannot be discounted. As our [OI]-derived H2O production rates are consistent with values derived using other methods, we conclude that the contribution of O2 photodissociation to the observed [O I] emission is at most 5-10% that of the contribution of H2O for ISON. This is consistent with the expected contribution of O2 photodissociation if O2/H2O  ∼  4%, meaning [O I] emission can still be utilized as a reliable proxy for H2O production in comets as long as O2/H2O  ≲  4%, similar to the abundance measured by the ROSINA instrument on Rosetta at comet 67P/Churyumov-Gerasimenko.

Icarus (In press)

DOI: 10.1016/j.icarus.2018.02.024 NASA ADS: 2018arXiv180206116M arXiv: 1802.06116

Thermal infrared and optical photometry of Asteroidal Comet C/2002 CE10

  • Tomohiko Sekiguchi 1
  • Seidai Miyasaka 2
  • Budi Dermawan 3
  • Thomas Mueller 4
  • Naruhisa Takato 5,6
  • Junichi Watanabe 5
  • Hermann Boehnhardt 7
  1. Hokkaido University of Education, Japan
  2. Tokyo Metropolitan Government, Japan
  3. Department of Astronomy, Indonesia
  4. Max-Planck-Institute for Extraterrestrial Physics, Germany
  5. National Astronomical Observatory of Japan, Japan
  6. Subaru Telescope, USA
  7. Max-Planck-Institute for Solar System Research, Germany

C/2002 CE10 is an object in a retrograde elliptical orbit with Tisserand parameter - 0.853 indicating a likely origin in the Oort Cloud. It appears to be a rather inactive comet since no coma and only a very weak tail was detected during the past perihelion passage. We present multi-color optical photometry, lightcurve and thermal mid-IR observations of the asteroidal comet. With the photometric analysis in BVRI, the surface color is found to be redder than asteroids, corresponding to cometary nuclei and TNOs/Centaurs. The time-resolved differential photometry supports a rotation period of 8.19 ± 0.05 h. The effective diameter and the geometric albedo are 17.9 ± 0.9 km and 0.03 ± 0.01, respectively, indicating a very dark reflectance of the surface. The dark and redder surface color of C/2002 CE10 may be attribute to devolatilized material by surface aging suffered from the irradiation by cosmic rays or from impact by dust particles in the Oort Cloud. Alternatively, C/2002 CE10 was formed of very dark refractory material originally like a rocky planetesimal. In both cases, this object lacks ices (on the surface at least). The dynamical and known physical characteristics of C/2002 CE10 are best compatible with those of the Damocloids population in the Solar System, that appear to be exhausted cometary nuclei in Halley-type orbits. The study of physical properties of rocky Oort cloud objects may give us a key for the formation of the Oort cloud and the solar system.

Icarus (In press)

DOI: 10.1016/j.icarus.2017.12.037 NASA ADS: 2018Icar..304...95S arXiv: 1712.08388

Strong CO+ and N2+ Emission in Comet C/2016 R2 (Pan-STARRS)

  • Anita Cochran 1
  • Adam McKay 2
  1. The University of Texas at Austin
  2. Goddard SFC and USRA

We report on imaging and spectroscopic observations of comet C/2016 R2 (Pan-STARRS) obtained with the 0.8 m and 2.7 m telescopes of McDonald Observatory in 2017 November and December, respectively. The comet was at a heliocentric distance greater than 3 au during both sets of observations. The images showed a well-developed tail with properties that suggested it was an ion tail. The spectra confirmed that we were observing well-developed bands of CO+ and N2+. The N2+ detection was unequivocally cometary and was one of the strongest bands of N2+ detected in a comet spectrum. We derived the ratio of these two ions and from that we were able to derive that N2/CO = 0.15. This is the highest such ratio reported for a comet.

This Letter includes data taken at The McDonald Observatory of The University of Texas at Austin.

The Astrophysical Journal Letters (Published)

DOI: 10.3847/2041-8213/aaab57 NASA ADS: 2018ApJ...854L..10C arXiv: 1801.01199

Isotopic ratios in outbursting comet C/2015 ER61

  • B. Yang 1,2
  • D. Hutsem 3
  • Y. Shinnaka 4
  • C. Opitom 1
  • J. Manfroid 3
  • E. Jehin 3
  • K. J. Meech 5
  • O. R. Hainaut 1
  • J. V. Keane 5
  • M. Gillon 3
  1. European Southern Observatory, Chile
  2. Yunnan Observatories, Chinese Academy of Sciences, China
  3. Institut d'Astrophysique et de Geophysique, Universite de Liege, Belgium
  4. National Astronomical Observatory of Japan, Japan
  5. Institute of Astronomy, University of Hawaii, USA

Isotopic ratios in comets are critical to understanding the origin of cometary material and the physical and chemical conditions in the early solar nebula. Comet C/2015 ER61 (PANSTARRS) underwent an outburst with a total brightness increase of 2 magnitudes on the night of 2017 April 4. The sharp increase in brightness offered a rare opportunity to measure the isotopic ratios of the light elements in the coma of this comet. We obtained two high-resolution spectra of C/2015 ER61 with UVES/VLT on the nights of 2017 April 13 and 17. At the time of our observations, the comet was fading gradually following the outburst. We measured the nitrogen and carbon isotopic ratios from the CN violet (0,0) band and found that 12C/13C=100 +/- 15, 14N/15N=130 +/- 15. In addition, we determined the 14N/15N ratio from four pairs of NH2 isotopolog lines and measured 14N/15N=140+/-28. The measured isotopic ratios of C/2015 ER61 do not deviate significantly from those of other comets.

Astronomy & Astrophysics (Published)

DOI:  10.1051/0004-6361/201732100 NASA ADS: 2018A&A...609L...4Y arXiv: 1712.02810