OSIRIS Observations of Asteroid 21 Lutetia: Geomorphology and Colour Variegation

On July 10, 2010, the ESA Rosetta mission successfully flew by the big asteroid 21 Lutetia. The scientific camera system OSIRIS took 462 images through 24 filters of the narrow angle (NAC) and wide angle (WAC) cameras. Near closest approach (CA) the whole body (northern hemisphere) of Lutetia was imaged with a scale of 60 m per pixel. As expected the surface morphology of Lutetia is dominated by large impact craters, some comparable to the radius of the asteroid. Smooth near craterless terrains indicate recent impacts and ejecta. Features found on discernable regional units include craters, grabens, scarps, pits, ridges, contacts, and large boulders. Craters with sharp and steep walls (some with landslides), some with irregular shapes and others almost filled with regolith are found. A topographic shape and photometric model of Lutetia as developed for the interpretation of the OSIRIS results of asteroid Steins (Jorda et al. 2010, Spjuth et al. 2010) will provide local slopes and gravity. The OSIRIS filters have been extensively calibrated in-flight and images will be used to construct photo-metrically accurate colour ratio maps which have been shown to be of importance for the study of geological units and morphological features.