  We have developed a self-consistent model of the disk around the nearby 10
Myr old star TW Hya which matches the observed spectral energy distribution and
7mm images of the disk. The model requires a significant dust size evolution
and a partially-evacuated inner disk region, as predicted by theories of planet
formation. The outer disk, which extends to at least 140 AU in radius, is very
optically thick at IR wavelengths and quite massive ~0.06 Msun for the
relatively advanced age of this T Tauri star. This implies long viscous and
dust evolution timescales, although dust must have grown to sizes of order ~1cm
to explain the sub-mm and mm spectral slopes. In contrast, the negligible
near-infrared excess emission of this system requires that the disk be
optically thin inside ~4 AU.This inner region cannot be completely evacuated;
we need ~0.5 lunar mass of ~1 micron particles remaining to produce the
observed 10 micron silicate emission. Our model requires a distinct transition
in disk properties at ~4 AU, separating the inner and outer disk. The inner
edge of the optically-thick outer disk must be heated almost frontally by the
star to account for the excess flux at mid-IR wavelengths. We speculate that
this truncation of the outer disk may be the signpost of a developing gap due
to the effects of a growing protoplanet; the gap is still presumably evolving
because material still resides in it, as indicated by the silicate emission,
the molecular hydrogen emission, and by the continued accretion onto the
central star (albeit at a much lower rate than typical of younger T Tauri
stars). TW Hya thus may become the Rosetta stone for our understanding of the
evolution and dissipation of protoplanetary disks.
