Cometary Science Newsletter

February 2016
Michael S. P. Kelley (

Postdoctoral position in cometary science at the Laboratoire d’Astrophysique de Marseille (France)

Applications are invited for a postdoctoral position in the area of cometary science at the Laboratoire d’Astrophysique de Marseille (LAM) in collaboration with O. Groussin, L. Jorda and O. Mousis.

The position is funded by the European Horizon 2020 research and innovation programme, and the successful applicant is expected to work on the analysis and scientific exploitation of Rosetta data, in the framework of the MIARD (Multi-Instruments Analysis of Rosetta Data) project.

The focus of this work is 1) to study the physical properties of the top 30 cm of the nucleus and its heterogeneity, 2) to identify and characterize the physical parameters controlling the non-gravitational forces of the nucleus, and 3) to constrain the formation conditions of the nucleus from its shape and composition.

Candidates interested in this position should have a PhD in astrophysics, physics or planetary science. Previous experience in cometary sciences is welcome but not mandatory.

The appointment is expected to start in June 2016, for a duration of 24 months maximum. Later start dates can be negotiated.

Applicants interested in this position should submit a CV, a list of publications, a description of their past and present research accomplishments, and 2-3 letters of reference. Please send applications and/or further inquiries to O. Groussin ( and L. Jorda (

Full consideration will be given to applications received by March 31, 2016.

PDF: Postdoctoral position in cometary science at the Laboratoire d’Astrophysique de Marseille (France)

Conference Announcements

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

Cometary Science After Rosetta: Future Directions

London, June 16-17, 2016

At this meeting, we shall review the current status of the field of cometary science following the keenly anticipated results of Rosetta, with the aim to engender focused, collaborative studies of these fascinating objects. The programme will include solicited presentations and talks and posters given by the attendees.

For an outline of the meeting, and to register your interest, please visit: .

This meeting will immediately follow the Royal Society Discussion Meeting: Cometary science after Rosetta, also to be held in London, on June 14-15: .

Organizers: Geraint Jones, Matt Taylor, Alan Fitzsimmons, Matthew Knight

Refereed Articles

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

Seasonal Evolution on the Nucleus of Comet C/2013 A1 (Siding Spring)

  • Jian-Yang Li (李荐扬) 1
  • Nalin H. Samarasinha 1
  • Michael S. P. Kelley 2
  • Tony L. Farnham 2
  • Dennis Bodewits 2
  • Carey M. Lisse 3
  • Max J. Mutchler 4
  • Michael F. A’Hearn 2
  • W. Alan Delamere 5
  1. Planetary Science Institute, 1700 E. Ft. Lowell Rd., Suite 106, Tucson, AZ 85719, USA
  2. Department of Astronomy, University of Maryland, College Park, MD 20742, USA
  3. Johns Hopkins University Applied Physics Laboratory, Space Department, 11100 Johns Hopkins Rd., Laurel, MD 20723, USA
  4. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218-2463, USA
  5. Delamere Support Service, Bolder, CO 80304, USA

We observed Comet C/Siding Spring using the Hubble Space Telescope (HST) during its close approach to Mars. The high spatial resolution images obtained through the F689M, F775W, and F845M filters reveal the characteristics of the dust coma. The dust production rate of C/Siding Spring, quantified by Afρ, is 590±30, 640±30, and 670±30 cm in a 420 km-radius aperture at 38° solar phase angle through the three filters, respectively, consistent with other observations at similar time and geometry, and with model predictions based on earlier measurements. The dust expansion velocity is ~150-250 m s−1 for micron-sized dust grains, similar to the speeds found for other comets. The coma has a color slope of (5.5±1.5)%/100 nm between 689 and 845 nm, similar to previous HST measurements at comparable aperture sizes, consistent with the lack of color dependence on heliocentric distance for almost all previously observed active comets. The rotational period of the nucleus of C/Siding Spring is determined from the periodic brightness variation in the coma to be 8.00±0.08 hours, with no excited rotational state detected. The dust coma shows a broad and diffuse fan-shaped feature in the sunward direction, with no temporal morphological variation observed. The projected orientation of the dust feature, combined with the previous analysis of the coma morphology and other characteristics, suggests secular activity evolution of the comet in its inner solar system passage as one previously observed active region turns off whereas new regions exposed to sunlight due to seasonal illumination change.

Astrophysical Journal Letters (In press)

DOI: 10.3847/2041-8205/817/2/L23 NASA ADS: 2016arXiv160103709L arXiv: 1601.03709

Dust Photophoretic transport around a T Tauri star: implications for comets composition

  • Cordier, D. 1
  • Prada Moroni, P. G. 2,4
  • Tognelli, E. 3,4
  1. GSMA - University of Reims, Reims, France.
  2. Physics Department "E. Fermi", University of Pisa, Largo B. Pontecorvo 3, I-56127, Pisa, Italy
  3. Department of Physics, University of Roma Tor Vergata, Via della Ricerca Scientifica 1, 00133, Roma, Italy
  4. INFN, Largo B. Pontecorvo 3, I-56127, Pisa, Italy

There is a growing body of evidences for the presence of crystalline material in comets. These crystals are believed to have been annealed in the inner part of the proto-solar nebula, while comets should have been formed in the outer regions. Several transport processes have been proposed to reconcile these two facts; among them a migration driven by photophoresis. The primarily goal of this work is to assess whether disk irradiation by a Pre-Main Sequence star would influence the photophoretic transport. To do so, we have implemented an evolving 1+1D model of an accretion disk, including advanced numerical techniques, undergoing a time-dependent irradiation, consistent with the evolution of the proto-Sun along the Pre-Main Sequence. The photophoresis is described using a formalism introduced in several previous works. Adopting the opacity prescription used in these former studies, we find that the disk irradiation enhances the photophoretic transport: the assumption of a disk central hole of several astronomical units in radius is no longer strictly required, whereas the need for an ad hoc introduction of photoevaporation is reduced. However, we show that a residual trail of small particles could annihilate the photophoretic driven transport via their effect on the opacity. We have also confirmed that the thermal conductivity of transported aggregates is a crucial parameter which could limit or even suppress the photophoretic migration and generate several segregation effects.

Icarus (In press)

DOI: 10.1016/j.icarus.2015.11.037 NASA ADS: 2016arXiv160102144C arXiv: 1601.02144