  We describe the first determination of thermal properties and size of the
M-type asteroid (16) Psyche from interferometric observations obtained with the
Mid-Infrared Interferometric Instrument (MIDI) of the Very Large Telescope
Interferometer. We used a thermophysical model to interpret our interferometric
data. Our analysis shows that Psyche has a low macroscopic surface roughness.
Using a convex 3-D shape model obtained by Kaasalainen et al. (2002, Icarus
159, 369-395), we derived a volume-equivalent diameter for (16) Psyche of 247
+- 25 km or 238 +- 24 km, depending on the possible values of surface
roughness. Our corresponding thermal inertia estimates are 133 or 114
J.m-2.s-0.5.K-1, with a total uncertainty estimated to 40 J.m-2.s-0.5.K-1. They
are among the highest thermal inertia values ever measured for an asteroid of
this size. We consider this as a new evidence of a metal-rich surface for the
asteroid (16) Psyche.
