Paper: astro-ph/0509434
Date: Thu, 15 Sep 2005 10:24:53 GMT (775kb)

Title: Thermal infrared observations of the Hayabusa spacecraft target asteroid
25143 Itokawa

Authors: T. G. Mueller, T. Sekiguchi, M. Kaasalainen, et al

Comments: 9 pages, 7 figures, accepted for publication by A&A 29/Aug/2005
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We obtained N- and Q-band observations of the Apollo-type asteroid 25143
Itokawa during its close Earth approach in July 2004 with TIMMI2 at the ESO 3.6
m telescope. Our photometric measurement, in combination with already published
data, allowed us to derive a radiometric effective diameter of 0.32+/-0.03 km
and an albedo of 0.19 +0.11/-0.03 through a thermophysical model. This
effective diameter corresponds to a slightly asymmetrical and flattened
ellipsoid of the approximate size of 520(+/-50) x 270(+/-30) x 230(+/-20) m,
based on the Kaasalainen et al. (2005) shape model. Our studies show that the
thermal observations lead to size estimates which are about 15% smaller than
the radar results (Ostro et al. 2005), slightly outside the stated radar
uncertainties of +/-10%. We determined a rather high thermal inertia of 750
Jm-2s-0.5K-1. This is an indication for a bare rock dominated surface, a thick
dust regolith can be excluded as well as a metallic surface. From our data we
constructed a 10.0 micrometer thermal lightcurve which is nicely matched in
amplitude and phase by the shape and spin vector solution in combination with
our TPM description. The assumed S-type bulk density in combination with
radiometric size lead to a total mass estimate of 4.5 +2.0/-1.8 x 10^10 kg.

\\ ( http://arXiv.org/abs/astro-ph/0509434 , 775kb)