Cometary Science Newsletter

July 2016
Michael S. P. Kelley (

Conference Announcements

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

COMETS 2016 - Reminder: Abstract and Registration are open

Don't forget!

Important dates:

Abstract deadline: July 4, 2016

Early bird registration deadline: October 1, 2016

For more information about the conference, visit

If you have questions or need assistance during the registration process, please send an email to and reference Comets 2016 in the subject.

The organising committee

Refereed Articles

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

Dust Impact Monitor (SESAME-DIM) on board Rosetta/Philae: Millimetric particle flux at comet 67P/Churyumov-Gerasimenko

  • Hirn, A. 1,2
  • Albin, T. 3,4,2
  • Apáthy, I. 1
  • Della Corte, V. 5
  • Fischer, H.-H. 6
  • Flandes, A. 7,2
  • Loose, A. 2
  • Péter, A. 1
  • Seidensticker, K. J. 8
  • Krüger, H. 2
  1. Centre for Energy Research, Hungarian Academy of Sciences, Hungary
  2. Max-Planck-Institut für Sonnensystemforschung, Germany
  3. Institut für Raumfahrtsysteme, University Stuttgart, Germany
  4. Medical Radiation Physics, Faculty VI, Carl von Ossietzky University, Germany
  5. Institute for Space Astrophysics and Planetology (IAPS), National Institute for AstroPhysics (INAF), Italy
  6. Deutsches Zentrum für Luft- und Raumfahrt, Raumflugbetrieb und Astronautentraining, MUSC, Germany
  7. Ciencias Espaciales, Instituto de Geofísica, Universidad Nacional Autónoma de México, Mexico
  8. Deutsches Zentrum für Luft- und Raumfahrt, Institut für Planetenforschung, Germany

The Philae lander of the Rosetta mission, aimed at the in situ investigation of comet 67P/C-G, was deployed to the surface of the comet nucleus on 12 Nov 2014 at 2.99 AU heliocentric distance. The Dust Impact Monitor (DIM) as part of the Surface Electric Sounding and Acoustic Monitoring Experiment (SESAME) on the lander employed piezoelectric detectors to detect the submillimetre- and millimetre-sized dust and ice particles emitted from the nucleus. We determine the upper limit of the ambient flux of particles in the measurement range of DIM based on the measurements performed with the instrument during Philae's descent to its nominal landing site Agilkia at distances of about 22 km, 18 km, and 5 km from the nucleus barycentre and at the final landing site Abydos. The geometric factor of the DIM sensor is calculated assuming an isotropic ambient flux of the submillimetre- and millimetre-sized particles. For the measurement intervals when no particles were detected the maximum true impact rate was calculated by assuming Poisson distribution of the impacts, and it was given as the detection limit at a 95% confidence level. Based on measurements performed with DIM, the upper limit of the flux of particles in the measurement range of the instrument was of the order of 10−8−10−7m−2s−1sr−1 during descent and 1.6⋅10−9m−2s−1sr−1 at Abydos on 13 and 14 Nov 2014. Considering particle speeds below escape velocity, the upper limit for the volume density of particles in the measurement range of DIM was constrained to 10−11m−3−10−12m−3. Results of the calculations performed with the GIPSI tool on the expected particle fluxes during the descent of Philae were compatible with the non-detection of compact particles by the DIM instrument.

Astronomy and Astrophysics (In press)

DOI: 10.1051/0004-6361/201628370 arXiv: 1605.06291

Fission and reconfiguration of bilobate comets as revealed by 67P/Churyumov–Gerasimenko

  • Hirabayashi, M. 1
  • Scheeres, D.J. 1
  • Chesley, S.R. 2
  • Marchi, S. 3
  • McMahon, J.W. 1
  • Steckloff, J. 4
  • Mottola, S. 5
  • Naidu, S.P. 2
  • Bowling, T. 6
  1. University of Colorado, Boulder, CO
  2. Jet Propulsion Laboratory, Pasadena, CA
  3. Southwest Research Institute, Boulder, CO
  4. Purdue University, West Lafayette, IN
  5. German Aerospace Center (DLR), Berlin, Gemany
  6. University of Chicago, Chicago, IL

The solid, central part of a comet—its nucleus—is subject to destructive processes1, 2, which cause nuclei to split at a rate of about 0.01 per year per comet3. These destructive events are due to a range of possible thermophysical effects4; however, the geophysical expressions of these effects are unknown. Separately, over two-thirds of comet nuclei that have been imaged at high resolution show bilobate shapes5, including the nucleus of comet 67P/Churyumov–Gerasimenko (67P), visited by the Rosetta spacecraft. Analysis of the Rosetta observations suggests that 67P’s components were brought together at low speed after their separate formation6. Here, we study the structure and dynamics of 67P’s nucleus. We find that sublimation torques have caused the nucleus to spin up in the past to form the large cracks observed on its neck. However, the chaotic evolution of its spin state has so far forestalled its splitting, although it should eventually reach a rapid enough spin rate to do so. Once this occurs, the separated components will be unable to escape each other; they will orbit each other for a time, ultimately undergoing a low-speed merger that will result in a new bilobate configuration. The components of four other imaged bilobate nuclei have volume ratios that are consistent with a similar reconfiguration cycle, pointing to such cycles as a fundamental process in the evolution of short-period comet nuclei. It has been shown7, 8 that comets were not strong contributors to the so-called late heavy bombardment about 4 billion years ago. The reconfiguration process suggested here would preferentially decimate comet nuclei during migration to the inner solar system, perhaps explaining this lack of a substantial cometary flux.

Nature (Published)

DOI: 10.1038/nature17670

  • Dello Russo, N. 1
  • Kawakita, H. 2
  • Vervack, R. J. 1
  • Weaver, H. A. 1
  1. The Johns Hopkins University Applied Physics Laboratory, Laurel, MD
  2. Koyama Astronomical Observatory, Kyoto Sangyo University, Japan

A systematic analysis of the mixing ratios with respect to H2O for eight species (CH3OH, HCN, NH3, H2CO, C2H2, C2H6, CH4, and CO) measured with high-resolution infrared spectroscopy in thirty comets between 1997 and 2013 is presented. Some trends are beginning to emerge when mixing ratios in individual comets are compared to average mixing ratios obtained for all species within the population. The variation in mixing ratios for all measured species is at least an order of magnitude. Overall, Jupiter-family comets are depleted in volatile species with respect to H2O compared to long-period Oort cloud comets, with the most volatile species showing the greatest relative depletion. There is a high positive correlation between the mixing ratios of HCN, C2H6, and CH4, whereas NH3, H2CO, and C2H2 are moderately correlated with each other but generally uncorrelated or show only weak correlation with other species. CO is generally uncorrelated with the other measured species possibly because it has the highest volatility and is therefore more susceptible to thermal evolutionary effects. Most of these correlations appear to be independent of dynamical class with a few possible exceptions. Molecular mixing ratios for CH3OH, HCN, C2H6, and CH4 show an expected behavior with heliocentric distance suggesting a dominant ice source, whereas there is emerging evidence that the mixing ratios of NH3, H2CO, C2H2, NH2, and CN may increase at small heliocentric distances, suggesting the possibility of additional sources related to the thermal decomposition of organic dust. Although this provides information on the composition of the most volatile grains in comets, it presents an additional difficulty in classifying comet chemistry because most comets within this dataset were only observed over a limited range of heliocentric distance. Although there is remarkable compositional diversity resulting in a unique chemical fingerprint for each comet, a hierarchical tree cluster analysis is used to determine a taxonomic classification system containing four groups and eleven subgroups. Optical and infrared comparisons indicate that mixing ratios of daughter species and potential parents from cometary ices are sometimes but not always consistent with one another. This suggests that in many comets there are significant sources of C2 and/or CN from grains, and that the importance of these sources is variable within the comet population.

Icarus (In press)

DOI: 10.1016/j.icarus.2016.05.039