Cometary Science Newsletter

Issue
18
Month
September 2016
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

Post-doctoral position: Rosetta infrared molecular data

A 2-year post-doctoral position in cometary science is opened at the Observatory of Paris (LESIA, CNRS, Meudon), beginning in fall 2016.

The successfull applicant will analyse infrared spectra of the atmosphere of comet 67P/Churyomov-Gerasimenko obtained with the high-spectral resolution channel of the VIRTIS/Rosetta instrument (Visible Infrared Thermal Imaging Spectrometer) built at the Observatory of Paris. The project will focuss on the study of the distributions of H2O and CO2 gases, and their seasonal, diurnal, and regional variations to understand the processes which control cometary activity. Other topics of interest could be considered.

The applicant will benefit of a dynamic research environment, with the possibility to interact with scientists involved in several Rosetta instruments. Conference travel and equipment support will be provided.

A PhD in astrophysics is required. The following skills will be considered in the evaluation process of the applicants:

  • working knowledge in planetary science, and comets
  • expertise in the reduction of infrared spectroscopic observations
  • knowledge in radiative transfer
  • previous experience in space missions, in particular Rosetta, is an asset.

Applicants should submit a curriculum vitae with a list of publications, a short review of previous works and statement of research interest. They should arrange for two reference letters. Applications should be sent via email to dominique.bockelee@obspm.fr. The closing date is 25 September 2016. Late applications can be considered, until the position is filled.

The project is funded by Paris Sciences Lettres University (program IRIS OCAV).

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.

174P/Echeclus

This comet has gone into outburst. The initial report, by Paul Camilleri to the Yahoo Comets Mailing List, and subsequent follow-up by other observers, including Tony Angel, Alan Hale, Jean-Francois Soulier, Lucian Hudin, and Richard Miles, indicates a strength of approximately 2.5 magnitudes, occurring between 2016 Aug 27.7 and 28.8 UT. After the outburst, the comet had a stellar appearance and a total apparent brightness of ~15.2 mag. The comet has a Centaur class orbit, and is presently at 6.3 au from the Sun, and 5.5 au from the Earth.

- Mike Kelley, UMD

Refereed Articles

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

The primordial nucleus of comet 67P/Churyumov-Gerasimenko

  • B. J. R. Davidsson 1,2
  • H. Sierks 3
  • C. Güttler 3
  • F. Marzari 4
  • M. Pajola 5
  • H. Rickman 1,6
  • M. F. A’Hearn 7,8
  • A.-T. Auger 9
  • M. R. El-Maarry 10
  • S. Fornasier 11
  • P. J. Gutiérrez 12
  • H. U. Keller 13
  • M. Massironi 5,14
  • C. Snodgrass 15
  • J.-B. Vincent 3
  • and 33 co-authorsNone
  1. Department of Physics and Astronomy, Uppsala University,, Sweden
  2. Jet Propulsion Laboratory, Pasadena (CA), USA
  3. Max–Planck–Institut für Sonnensystemforschung, Göttingen, Germany
  4. University of Padova, Italy
  5. CISAS, University of Padova, Italy
  6. PAN Space Research Center, Warszawa, Poland
  7. University of Maryland, College Park (MD), USA
  8. Gauss Professor, Akademie der Wissenschaften zu Göttingen, Germany
  9. Aix-Marseille Université, CNRS, LAM, Marseille, France
  10. Physikalisches Institut der Universität Bern, Switzerland
  11. LESIA–Observatoire de Paris, CNRS, Meudon, France
  12. Instituto de Astrofísica de Andalucía (CSIC), Granada, Spain
  13. IGEP, Technische Universität Braunschweig, Germany
  14. Dipartimento di Geoscienze, University of Padova, Italy
  15. Planetary and Space Sciences, The Open University, Milton Keynes, UK

We investigate the formation and evolution of comet nuclei and other trans-Neptunian objects (TNOs) in the solar nebula and primordial disk prior to the giant planet orbit instability foreseen by the Nice model.

Our goal is to determine whether most observed comet nuclei are primordial rubble-pile survivors that formed in the solar nebula and young primordial disk or collisional rubble piles formed later in the aftermath of catastrophic disruptions of larger parent bodies. We also propose a concurrent comet and TNO formation scenario that is consistent with observations.

We used observations of comet 67P by the ESA Rosetta spacecraft combined with data from the NASA Stardust sample-return mission to comet 81P and from meteoritics; we also used existing observations from ground or from spacecraft of irregular satellites of the giant planets, Centaurs, and TNOs. We find that thermal processing due to short-lived radionuclides, combined with collisional processing during accretion in the primordial disk, creates a population of medium-sized bodies that are comparably dense, compacted, strong, and heavily depleted in supervolatiles like CO and CO2; they contain little to no amorphous water ice, and have experienced extensive metasomatism and aqueous alteration due to liquid water. Irregular satellites Phoebe and Himalia are potential representatives of this population. Collisional rubble piles inherit these properties from their parents. Contrarily, comet nuclei have low density, high porosity, weak strength, are rich in supervolatiles, may contain amorphous water ice, and do not display convincing evidence of in situ metasomatism or aqueous alteration. We outline a comet formation scenario that starts in the solar nebula and ends in the primordial disk, that reproduces these observed properties, and additionally explains the presence of extensive layering on 67P and 9P, its bi-lobed shape, the extremely slow growth of comet nuclei as evidenced by recent radiometric dating, and the low collision probability that allows primordial nuclei to survive the age of the solar system.

We conclude that observed comet nuclei are primordial rubble piles, and not collisional rubble piles. We argue that TNOs formed as a result of streaming instabilities at sizes below ~400 km and that ~350 of these grew slowly in a low-mass primordial disk to the size of Triton, Pluto, and Eris, causing little viscous stirring during growth. We thus propose a dynamically cold primordial disk, which prevented medium-sized TNOs from breaking into collisional rubble piles and allowed the survival of primordial rubble-pile comets. We argue that comets formed by hierarchical agglomeration out of material that remained after TNO formation, and that this slow growth was a necessity to avoid thermal processing by short-lived radionuclides that would lead to loss of supervolatiles, and that allowed comet nuclei to incorporate ~3 Myr old material from the inner solar system.

Editor's note: This abstract has been edited for length.

Astronomy & Astrophysics (Published)

DOI: 10.1051/0004-6361/201526968

Optical Spectroscopy of Comet C/2014 Q2 (Lovejoy) from MIRO

  • Kumar Venkataramani 1,2
  • Satyesh Ghetiya 1,3
  • Shashikiran Ganesh 1
  • U.C.Joshi 1
  • Vikrant K. Agnihotri 4
  • K.S.Baliyan 1
  1. Physical Research Laboratory, Ahmedabad, India
  2. Indian Institute of Technology Gandhinagar
  3. Indian Institute of Space Science and Technology, Thiruvananthapuram, India
  4. Cepheids Astronomy, Kota, India

Spectra of comet C/2014 Q2 (Lovejoy) were taken with a low resolution spectrograph mounted on the 0.5 m telescope at the Mount Abu Infrared Observatory (MIRO), India during January to May 2015 covering the perihelion and post-perihelion periods. The spectra showed strong molecular emission bands (C2, C3 and CN) in January, close to perihelion. We have obtained the scale lengths for these molecules by fitting the Haser model to the observed column densities. The variation of gas production rates and production rate ratios with heliocentric distance were studied. The extent of the dust continuum using the Af-rho parameter and its variation with the heliocentric distance were also investigated. The comet is seen to become more active in the post-perihelion phase, thereby showing an asymmetric behaviour about the perihelion.

Monthly Notices of the Royal Astronomical Society (In press)

arXiv: 1607.06682