  Circumstellar debris disks are the extrasolar analogues of the asteroid belt
and the Kuiper belt. They consist of comets and leftover planetesimals that
continuously collide and produce circumstellar dust that can be observed as
infrared excess or in resolved imaging. As an obvious outcome of the planet
formation process, debris disks can help us constrain planet formation theories
and learn about the history of our own solar system. This thesis presents
observational studies of secondary gas in debris disks. It also discusses the
astrobiological potential of debris disks created during impact events onto
exoplanets.
