Cometary Science Newsletter

Issue
12
Month
March 2016
Editor
Michael S. P. Kelley (msk@astro.umd.edu)

Conference Announcements

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

Second Announcement: Cometary Science after Rosetta Meetings, London, June 14-17

Meeting I: June 14-15: Cometary Science after Rosetta
The Royal Society, London

Results from the European Space Agency’s Rosetta mission to Comet 67P/Churyumov-Gerasimenko are leading to a revolution in our understanding of these ancient bodies, and hence the conditions prevalent in the early Solar System. This meeting will report, through solicited reviews and a contributed poster session, on all aspects of the mission's ground-breaking discoveries, placing them in the context of cometary science as a whole. Contributions to the poster session are welcome.

Registration and abstract submission now open at:
https://royalsociety.org/events/2016/06/cometary-science/
Poster Abstract deadline: March 18, 2016.

Meeting II: June 16-17: Cometary Science After Rosetta: Future Directions
The Centre for Planetary Sciences at UCL/Birkbeck

At this second meeting, we shall further 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 as well as contributed talks and posters.

Abstract submission and registration now open at:
http://www.ucl.ac.uk/mssl/planetary-science/comets-after-rosetta
Abstract deadline: April 30, 2016.

Refereed Articles

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

Distant activity of 67P/Churyumov-Gerasimenko in 2014: Ground-based results during the Rosetta pre-landing phase

  • Snodgrass, C. 1
  • and 16 co-authorsNone
  1. The Open University, UK

As the ESA Rosetta mission approached, orbited, and sent a lander to comet 67P/Churyumov-Gerasimenko in 2014, a large campaign of ground-based observations also followed the comet. We constrain the total activity level of the comet by photometry and spectroscopy to place Rosetta results in context and to understand the large-scale structure of the comet's coma pre-perihelion. We performed observations using a number of telescopes, but concentrate on results from the 8m VLT and Gemini South telescopes in Chile. We use R-band imaging to measure the dust coma contribution to the comet's brightness and UV-visible spectroscopy to search for gas emissions, primarily using VLT/FORS. In addition we imaged the comet in near-infrared wavelengths (JHK) in late 2014 with Gemini-S/Flamingos 2. We find that the comet was already active in early 2014 at heliocentric distances beyond 4 au. The evolution of the total activity (measured by dust) followed previous predictions. No gas emissions were detected despite sensitive searches. The comet maintains a similar level of activity from orbit to orbit, and is in that sense predictable, meaning that Rosetta results correspond to typical behaviour for this comet. The gas production (for CN at least) is highly asymmetric with respect to perihelion, as our upper limits are below the measured production rates for similar distances post-perihelion in previous orbits.

Astronomy and Astrophysics (In press)

DOI: 10.1051/0004-6361/201527834 arXiv: 1602.01493

The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 au heliocentric distance range inbound

  • Moreno, F. 1
  1. Instituto de Astrofísica de Andalucía, Spain

The ESA Rosetta spacecraft, currently orbiting around comet 67P, has already provided in situ measurements of the dust grain properties from several instruments, particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution. To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014. A Monte Carlo dust tail code has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately. The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is α=--3, instead of α=--2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 au, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 au. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment.

Astronomy and Astrophysics (In press)

DOI: http://dx.doi.org/10.1051/0004-6361/201527564 arXiv: 1602.01965

Comet 252P/LINEAR: Born (Almost) Dead?

  • Ye, Quan-Zhi 1
  • Brown, Peter G. 1,2
  • Wiegert, Paul A. 1,2
  1. Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
  2. Centre for Planetary Science and Exploration, The University of Western Ontario, London, ON N6A 5B8, Canada

Previous studies have revealed Jupiter-family comet 252P/LINEAR as a comet that was recently transported into the near-Earth object (NEO) region in ~1800 AD yet only being weakly active. In this Letter, we examine the "formed (almost) dead" hypothesis for 252P/LINEAR using both dynamical and observational approaches. By statistically examining the dynamical evolution of 252P/LINEAR over a period of 107 years, we find the median elapsed residency in the NEO region to be 4 × 102 years, which highlights the likelihood of 252P/LINEAR as an (almost) first-time NEO. With available cometary and meteor observations, we find the dust production rate of 252P/LINEAR to be on the order of 106 kg per orbit since its entry to the NEO region. These two lines of evidence support the hypothesis that the comet was likely to have formed in a volatile-poor environment. Cometary and meteor observations during the comet's unprecedented close approach to the Earth around 2016 March 21 would be useful for understanding of the surface and evolutionary properties of this unique comet.

Astrophysical Journal Letters (Published)

DOI: 10.3847/2041-8205/818/2/L29 arXiv: 1601.07837

Statistical ortho-to-para ratio of water desorbed from ice at 10 kelvin

  • Hama, T. 1
  • Kouchi, A. 1
  • Watanabe, N. 1
  1. Institute of Low Temperature Science, Hokkaido University, Sapporo 060–0819, Japan.

The anomalously low ortho-to-para ratios (OPRs) exhibited by gaseous water in space have been used to determine the formation temperature (<50 kelvin) of ice on cold interstellar dust. This approach assumes that the OPR of water desorbed from ice is related to the ice formation temperature on the dust. However, we report that water desorbed from ice at 10 kelvin shows a statistical high-temperature OPR of 3, even when the ice is produced in situ by hydrogenation of O2, a known formation process of interstellar water. This invalidates the assumed relation between OPR and temperature. The necessary reinterpretation of the low OPRs will help elucidate the chemical history of interstellar water from molecular clouds and processes in the early solar system, including comet formation.

Science (Published)

DOI: 10.1126/science.aad4026

The dust environment of comet 67P/Churyumov-Gerasimenko from Rosetta OSIRIS and VLT observations in the 4.5 to 2.9 au heliocentric distance range inbound

  • F. Moreno 1
  • C. Snodgrass 2
  • O. Hainaut 3
  • C. Tubiana 4
  • H. Sierks 4
  • and 49 co-authorsNone
  1. Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
  2. Planetary and Space Sciences, Department of Physical Sciences, The Open University, Walton Hall, Milton Keynes, Buckinghamshire MK7 6AA, UK
  3. European Southern Observatory, Karl-Schwarschild-Strasse 2, D-85748 Garching bei Muünchen, Germany
  4. Max-Planck Institut für Sonnensystemforschung, Justus-von-Liebig-Weg, 3 37077 Göttingen, Germany

Context. The ESA Rosetta spacecraft, currently orbiting around comet 67P, has already provided in situ measurements of the dust grain properties from several instruments, particularly OSIRIS and GIADA. We propose adding value to those measurements by combining them with ground-based observations of the dust tail to monitor the overall, time-dependent dust-production rate and size distribution.

Aims. To constrain the dust grain properties, we take Rosetta OSIRIS and GIADA results into account, and combine OSIRIS data during the approach phase (from late April to early June 2014) with a large data set of ground-based images that were acquired with the ESO Very Large Telescope (VLT) from February to November 2014.

Methods. A Monte Carlo dust tail code, which has already been used to characterise the dust environments of several comets and active asteroids, has been applied to retrieve the dust parameters. Key properties of the grains (density, velocity, and size distribution) were obtained from Rosetta observations: these parameters were used as input of the code to considerably reduce the number of free parameters. In this way, the overall dust mass-loss rate and its dependence on the heliocentric distance could be obtained accurately.

Results. The dust parameters derived from the inner coma measurements by OSIRIS and GIADA and from distant imaging using VLT data are consistent, except for the power index of the size-distribution function, which is –3, instead of –2, for grains smaller than 1 mm. This is possibly linked to the presence of fluffy aggregates in the coma. The onset of cometary activity occurs at approximately 4.3 au, with a dust production rate of 0.5 kg/s, increasing up to 15 kg/s at 2.9 au. This implies a dust-to-gas mass ratio varying between 3.8 and 6.5 for the best-fit model when combined with water-production rates from the MIRO experiment.

Astronomy and Astrophysics (In press)

arXiv: 1602.01965