16228

In the era of HST comma JWST comma and ALMA comma the initial conditions of planet formation will be laid bare through the direct imaging of planet forming regions around nearby young stars. As more and more disks are observed over multiple epochs comma their dynamic and variable natures are revealed comma opening new avenues of study. Archival HST images of TW Hya.s outer disk show that it has a shadow that orbits with a period of virgul16 yr comma but the full orbit of the shadow has not been observed comma leaving ambiguity about its origin. We propose to observe TW Hya over the next three Cycles with HST-STIS coronagraphy to fill in badly needed orbital phase coverage of the shadow.s motion and create a homogenous comma high quality dataset with archival STIS observations. Our program will elucidate the physical origin of the shadow and constrain the structure of TW Hya.s inner cavity independently from sub-mm imaging. Disk shadow imaging is a new tool for understanding the initial conditions of planet formation at radii inaccessible by other observations.