A Survey for Molecular Hydrogen Emission Around Stars Forming Terrestrial Planets

There is a discrepancy between the frequency of rocky planets in the inner AU known around Sun-like stars and the frequency of stars observed to be undergoing the collisions that form these planets. The discrepancy may indicate that rocky planets are less common than believed or that they form very differently than we have imagined, producing little or no debris signature. A third, less dramatic possibility is that planet-forming systems retain a tenuous reservoir of gas that whisks away the warm dust (debris) produced by planet-forming collisions. Over the past decade, it has been recognized that fluorescent FUV molecular hydrogen emission is an excellent tracer of gas in the planet forming regions of disks around young stars. We are using HST+COS with the G130M grating to survey the FUV spectrum between 1100 - 1370 Å for molecular hydrogen emission from a sample of 30 stars in the 11 Myr old Upper Scorpious star forming region. These data will test whether small amounts of disk gas remove the debris from planet forming collisions, or whether rocky planet formation possibly proceeds much differently than currently thought. Here we report initial results from this survey.