  We present Very Large Array observations at 3.5 cm of the nearby young star
TW Hya that show the emission is constant in time over weeks, months and years,
and spatially resolved with peak brightness temperature ~10 K at ~0.25 (15 AU)
resolution. These features are naturally explained if the emission mechanism at
this wavelength is thermal emission from dust particles in the disk surrounding
the star. To account quantitatively for the observations, we construct a
self-consistent accretion disk model that incorporates a population of
centimeter size particles that matches the long wavelength spectrum and spatial
distribution. A substantial mass fraction of orbiting particles in the TW Hya
disk must have agglomerated to centimeter size. These data provide the first
clear indication that dust emission from protoplanetary disks may be observed
at centimeter wavelengths, and that changes in the spectral slope of the dust
emission may be detected, providing constraints on dust evolution and the
planet formation process.
