Cometary Science Newsletter

May 2017
Michael S. P. Kelley (

Small Bodies Planetary Astronomy Python Package

We are proposing a dedicated Python package for use in small bodies planetary astronomy (asteroids and comets). The idea is to include well-tested routines that are widely used in our field to prevent people from re-inventing the wheel time and again. The goal would be to produce a package that will eventually be added as an Astropy affiliated package, meeting all of their high-level standards and building upon existing functionality.

We would like to know from you, as a potential user, what features you would be interested in. Also, if you are interested in contributing, either by doing actual Python programming for this package or simply contributing existing code (Python or any other common language, your contribution will be properly acknowledged), please let us know.

We created a google form for you to provide us feedback:

If you have questions, feel free to contact us directly:
M. Mommert ( and M. S. P. Kelley (

Refereed Articles

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

JCMT Spectral and Continuum Imaging of Comet 252P/LINEAR

  • Iain M. Coulson 1
  • Martin A. Cordiner 2
  • Yi-Jehng Kuan 3
  • Wei-Ling Tseng 3
  • Yo-Ling Chuang 3
  • Zhong-Yi Lin 4
  • Stefanie N. Milam 2
  • Steven B. Charnley 2
  • Wing-Huen Ip 4
  1. East Asian Observatory, 660 N.A'ohoku Place, Hilo, HI 96720, USA
  2. NASA Goddard Space Flight Center, 880 Greenbelt Road, Greenbelt, MD 20771, USA
  3. National Taiwan Normal University, Earth Sciences, 88 Sec.4, Ting-Chou Road, Taipei 11677, Taiwan
  4. National Central University, No. 300 Zhongda Road, Zhongli District, Taoyuan City 32001, Taiwan

Comet 252P/LINEAR passed the Earth at a distance of 0.035 au on 2016 March 21, presenting a rare opportunity to study a comet at high spatial resolution. Even with a single dish facility such as JCMT, the chemical structure of the coma could be observed on scales of 500–1000 km, which are smaller than the scale lengths of known distributed cometary molecules. Our week-long observing campaign at JCMT started on March 27 (UT), 12 days after perihelion, and ended on April 3, during which time the comet's distance from Earth increased from 0.045 to 0.078 au. Our observations of the J = 4 - 3 transition of HCN showed generally uniform levels of activity. Expansion velocities were ~0.6 km s-1 (±10%), and the derived mean HCN production rate during the week was 6.4 × 1024 mol s-1. Comparison with independent estimates of the water production rate during the same period yields a mixing ratio of 0.12% with respect to water. Methanol emissions appear to arise from an extended source—probably in the form of an ice halo—suggesting that all the gases from 252P may originate in large part from the sublimation of icy grains in the coma. Adopting a mean dust particle size of 1 mm, the mass of dust in the coma at the same time is estimated at 4 × 107 kg, implying a total dust production rate of 4 kg s-1. The dust-to-gas mass ratio of ~0.025 is one of the lowest values ever observed for a comet.

The Astronomical Journal (Published)

DOI: 10.3847/1538-3881/aa6440 NASA ADS: 2017AJ....153..169C

Seasonal changes of the volatile density in the coma and on the surface of comet 67P/Churyumov-Gerasimenko

  • Kramer, T. 1,2
  • Läuter, M. 1
  • Rubin, M. 3
  • Altwegg, K. 3
  1. Zuse Institute Berlin, 14195 Berlin, Germany
  2. Department of Physics, Harvard University, Cambridge, MA 02138, USA
  3. University of Bern, Space Research and Planetary Sciences, 3012 Bern, Switzerland

Starting from several monthly data sets of Rosetta's COmetary Pressure Sensor we reconstruct the gas density in the coma around comet 67P/Churyumov-Gerasimenko. The underlying inverse gas model is constructed by fitting ten thousands of measurements to thousands of potential gas sources distributed across the entire nucleus surface. The ensuing self-consistent solution for the entire coma density and surface activity reproduces the temporal and spatial variations seen in the data for monthly periods with Pearson correlation coefficients of 0.93 and higher. For different seasonal illumination conditions before and after perihelion we observe a systematic shift of gas sources on the nucleus.

Monthly Notices of the Royal Astronomical Society (In press)

DOI: 10.1093/mnras/stx866 arXiv: 1704.03874

Physical and dynamical properties of the anomalous comet 249P/LINEAR

  • Julio A. Fernández 1
  • Javier Licandro 2,3
  • Fernando Moreno 4
  • Andrea Sosa 5
  • Antonio Cabrera-Lavers 2,6
  • Julia de León 2,3
  • Peter Birtwhistle 7
  1. Departamento de Astronomía, Facultad de Ciencias, Universidad de la República, Iguá 4225, 14000 Montevideo, Uruguay
  2. Instituto de Astrofísica de Canarias (IAC), C/Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
  3. Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
  4. Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
  5. PDU Ciencias Físicas, Centro Universitario de la Región Este (CURE), Universidad de la República, 27000 Rocha, Uruguay
  6. Gran Telescopio Canarias (GTC), E-38712, Breña Baja, La Palma, Spain
  7. Great Shefford Observatory, Phlox Cottage, Wantage Road, Great Shefford, Berkshire RG17 7DA, United Kingdom

Images and low-resolution spectra of the near-Earth Jupiter family comet (JFC) 249P/LINEAR in the visible range obtained with the instrument OSIRIS in the 10.4m Gran Telescopio Canarias (GTC) (La Palma, Spain) on January 3, 4, 6 and February 6, 2016 are presented, together with a series of images obtained with the 0.4m telescope of the Great Shefford Observatory obtained on Oct. 22 and 27, and Nov. 1 and 24, 2006. The reflectance spectrum of 249P is similar to that of a B-type asteroid. The comet has an absolute (visual) nuclear magnitude HV=17.0±0.4, which corresponds to a radius of about 1-1.3 km for a geometric albedo ~0.04-0.07. From the analysis of GTC images using a Monte Carlo dust tail code we find that the time of maximum dust ejection rate was around 1.6 days before perihelion. The analysis of the dust tails during the 2006 and 2016 perihelion approaches reveals that, during both epochs, the comet repeated the same dust ejection pattern, with a similar short-lived activity period of about 20 days (FWHM) around perihelion and a dust loss rate peaking at 145±50 kg/s. The total dust mass ejected during its last perihelion passage was (2.5±0.9)×108 kg, almost all this mass being emitted before the first observation of January 3, 2016. The activity onset, duration, and total ejected mass were very similar during the 2006 perihelion passage. This amount of dust mass is very low as compared with that from other active JFCs. The past orbital evolution of 249P and 100 clones were also followed over a time scale of ~5×104 yr. The object and more than 60% of the clones remained bound to the near-Earth region for the whole computed period, keeping its perihelion distance within the range q≃0.4-1.1 au. The combination of photometric and spectroscopic observations and dynamical studies show that the near-Earth comet 249P/LINEAR has several peculiar features that clearly differentiate it from typical JFCs. We may be in front of a new class of near-Earth JFC whose source region is not the distant trans-neptunian population, but much closer in the asteroid belt. Therefore, 249P/LINEAR may be a near-Earth counterpart of the so-called main-belt comets or active asteroids.

Icarus (In press)

arXiv: 1704.04639

The Destruction of an Oort Cloud in a rich stellar cluster

  • Nordlander, T. 1
  • Rickman, H. 1,2
  • Gustafsson, B. 1,3
  1. Division of Astronomy and Space Physics, Department of Physics and Astronomy, Uppsala University, Box 516, 75120 Uppsala, Sweden
  2. PAN Space Research Center, Bartycka 18A, 00716 Warszawa, Poland
  3. Nordita, Roslagstullsbacken 23, 10691 Stockholm, Sweden

It is possible that the formation of the Oort Cloud dates back to the earliest epochs of solar system history. At that time, the Sun was almost certainly a member of the stellar cluster, where it was born. Since the solar birth cluster is likely to have been massive (1000-10 000 Msol), and therefore long-lived, an issue concerns the survival of such a primordial Oort Cloud.

We have investigated this issue by simulating the orbital evolution of Oort Cloud comets for several hundred Myr, assuming the Sun to start its life as a typical member of such a massive cluster. We have devised a synthetic representation of the relevant dynamics, where the cluster potential is represented by a King model, and about 20 close encounters with individual cluster stars are selected and integrated based on the solar orbit and the cluster structure. Thousands of individual simulations are made, each including 3 000 comets with orbits with three different initial semi-major axes.

Practically the entire initial Oort Cloud is found to be lost for our choice of semi-major axes (5 000–20 000 au), independent of the cluster mass, although the chance of survival is better for the smaller cluster, since in a certain fraction of the simulations the Sun orbits at relatively safe distances from the dense cluster centre. For the range of birth cluster sizes that we investigate, a primordial Oort Cloud will likely survive only as a small inner core with semi-major axes < 3 000 au. Such a population of comets would be inert to orbital diffusion into an outer halo and subsequent injection into observable orbits. Some mechanism is therefore needed to accomplish this transfer, in case the Oort Cloud is primordial and the birth cluster did not have a low mass. From this point of view, our results lend some support to a delayed formation of the Oort Cloud, that occurred after the Sun had left its birth cluster.

Astronomy & Astrophysics (In press)

arXiv: 1704.03341