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 \pm 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 ( \pm 50 ) \times 270 ( \pm 30 ) \times 230 ( \pm 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 \pm 10 % .
We determined a rather high thermal inertia of 750 J m ^ { -2 } s ^ { -0.5 } K ^ { -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 \mu m 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 } \cdot 10 ^ { 10 } kg .