Geomorphology of 21 Lutetia from Rosetta/OSIRIS Observations

Abstract

The Rosetta spacecraft performed a fly-by of the asteroid, 21 Lutetia, on 10 July 2010. The closest approach (CA) distance was around 3160 km. The scientific imaging system, OSIRIS[1], acquired images throughout the fly-by through both its narrow-angle (NAC) and wide-angle (WAC) cameras. The highest spatial scale in the NAC was around 60 m px-1 (slightly higher spatial scale than the Galileo SSI at 243 Ida). At closest approach, the 100 km diameter asteroid filled the field of view of the NAC giving 2000 pixels across the object. The images reveal a remarkably diverse object characterized by the presence of geologically old surfaces, as witnessed by crater statistics, in close proximity to relatively recent, large impact craters. Grooves (aligned topographic structures) similar to but more weakly defined than those seen on the Martian moon, Phobos, are pervasive and are observed to cut many craters. Some are roughly concentric about the most recent impact craters, others are not. It is not clear, at this stage of the analysis, whether the most recent impacts were responsible for their production. Boulder fields with objects >200 m in diameter are evident. In the most extensive boulder field, the boulders appear to have been covered and possibly moved by landslides acting under the tenuous gravity. Downslope motion, indicative of destabilization through impact and seismic activity, has been observed on smaller bodies (e.g. Deimos and 433 Eros). Numerous unusual structures have also been observed although albedo markings, which cannot be attributed to topographic relief, are subtle and rare. The presentation will provide an overview of the highest resolution data and will detail some of these aspects. [1] Keller, H.U., and 68 colleagues, (2007), OSIRIS-The Scientific Camera System Onboard Rosetta, Space Sci. Rev., 128, 433-506.