Missing Water in the Beta Pictoris System
Debris disks are the dusty, gas-poor remnants of planetary system formation. These circumstellar disks represent the late stages of planet formation, in which most gas has dissipated and dust exists on scales from micrometer-sized grains to planetesimals. Collisions between kilometer-sized bodies produce dust and gas of secondary origin. An example of this is the spatially-resolved clump of CO gas observed in the debris disk system Beta Pictoris, which also hosts a confirmed planet.
If the CO emission is the result of collisions of objects with the same chemical composition as comets in the Solar System, we would expect water vapour to also be produced. Using Herschel/HIFI archival data I have examined the Beta Pictoris system for H2O emission lines. My analysis shows no such emission, putting instead an upper limit on the observed flux. This translates into an upper limit on the H2O gas mass which is inconsistent with the mass expected from colliding bodies of Solar System composition.
The results suggest either a very cold gas clump, an incomplete understanding of the gas-producing mechanism, or a chemical composition of the colliders different from Solar System comets.