Indications for Regolith on Itokawa from Thermal-Infrared Observations

Kurzfassung

We report preliminary results of thermal-infrared observations of the near-Earth asteroid (25143) Itokawa made with the ESO 3.6m telescope in 2001 and the NASA IRTF in 2004. Using these and data from the literature we investigated the size and thermal properties of Itokawa. We were not able to obtain an un-ambiguous result for Itokawa’s size but we could reliably constrain the thermal properties of the surface. We use a detailed thermophysical model accounting explicitly for Itokawa’s shape and spin state, heat conduction, and surface roughness. Our results indicate that Itokawa’s surface is dominated by regolith rather than by bare rock; a surface of bare rock only is ruled out, although boulders covering a moderate percentage of the surface are not excluded.