  We report on the thermal properties and composition of asteroid (2867) Steins
derived from an analysis of new Spitzer Space Telescope (SST) observations
performed in March 2008, in addition to previously published SST observations
performed in November 2005. We consider the three-dimensional shape model and
photometric properties derived from OSIRIS images obtained during the flyby of
the Rosetta spacecraft in September 2008, which we combine with a thermal model
to properly interpret the observed SST thermal light curve and spectral energy
distributions. We obtain a thermal inertia in the range 100\pm50 JK-1m-2s-1/2
and a beaming factor (roughness) in the range 0.7-1.0. We confirm that the
infrared emissivity of Steins is consistent with an enstatite composition. The
November 2005 SST thermal light curve is most reliably interpreted by assuming
inhomogeneities in the thermal properties of the surface, with two different
regions of slightly different roughness, as observed on other small bodies,
such as the nucleus of comet 9P/Tempel 1. Our results emphasize that the shape
model is important to an accurate determination of the thermal inertia and
roughness. Finally, we present temperature maps of Steins, as seen by Rosetta
during its flyby, and discuss the interpretation of the observations performed
by the VIRTIS and MIRO instruments.
