The Geomorphology of Comet Churymov-Gerasimenko As Revealed By Rosetta/Osiris: Implicationsfor Past Collisional Evolution

Thursday, 18 December 2014
Simone Marchi1, Michael F A'Hearn2, Cesare Barbieri3, M. Antonietta Barucci4, Sebastien Besse5, Gabriele Cremonese6, Wing-Huen Ip7, Horst Uwe Keller8, Detlef Koschny9, Ekkehard Kuhrt10, Philippe L Lamy11, Francesco Marzari3, Matteo Massironi12, Maurizio Pajola13, Hans Rickman14, Rafael Rodrigo15, Holger Sierks16, Colin Snodgrass17, Nicolas Thomas18 and Jean-Baptiste Vincent17, (1)Southwest Research Institute Boulder, Boulder, CO, United States, (2)University of Maryland College Park, College Park, MD, United States, (3)University of Padua, Padua, Italy, (4)Observatoire Paris, Paris, France, (5)European Space Agency, Villanueva De La Can, Spain, (6)INAF - Astronomical Observatory of Padova, Padova, Italy, (7)NCU National Central University of Taiwan, Jhongli, Taiwan, (8)Institute for Geophysics and Extraterrestrial Physics, Braunschweig, Germany, (9)European Space Research and Technology Centre, Noordwijk, Netherlands, (10)German Aerospace Center DLR Berlin, Berlin, Germany, (11)Astrophysics Laboratory of Marseilles, Marseilles, France, (12)Univ Padova, Padova, Italy, (13)CISAS - Center for Studies and Activities for Space, University of Padova, Padova, Italy, (14)Uppsala University, Department of Physics and Astronomy, Uppsala, Sweden, (15)IAA-CSIC, Granada, Spain, (16)Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany, (17)Max-Planck Institute for Solar System Research, Goettingen, Germany, (18)University of Bern, Bern, Switzerland
In this paper we present the major geomorphological features of comet Churymov-Gerasimenko (C-G), with emphasis on those that may have formed through collisional processes. The C-G nucleus has been imaged with the Rosetta/OSIRIS camera system at varying spatial resolution. At the moment of this writing the maximum spatial resolution achieved is ~20 meter per pixel, and it will improve to reach the unprecedented centimeter-scale in November 2014. This resolution should allow us to identify and characterize pits, lineaments and blocks that could be the result of collisional evolution. Indeed, C-G has spent some 1000 years on orbits crossing the main asteroid belt, and a much longer time in the outer solar system. Collisions may have, therefore, shaped the morphology of the nucleus in various ways. Previously imaged Jupiter Family Comets (e.g., Tempel 1) show significant numbers of pits and lineaments, some of which could be due to collisions. Additional proposed formation mechanisms are related to cometary activity processes, such as volatile outgassing.

In addition to small scale features, the overall shape of C-G could also provide insights into the role of collisional processes. A striking feature is that C-G's shape is that of a contact binarySimilar shapes have been observed on rocky asteroids (e.g., Itokawa) and are generally interpreted as an indication of their rubble pile nature. A possibility is that C-G underwent similar processes, and therefore it may be constituted by reaccumulated fragments ejected from a larger precursor. An alternative view is that the current shape is the result of inhomogeneous outgassing activity, which may have dug a ~1-km deep trench responsible for the apparent contact binary shape.

The role of the various proposed formation mechanisms (collisional vs outgassing) for both small scale and global features will be investigated and their implications for the evolution of C-G will be discussed.