Circumstellar Disk Evolution: Constraining Theories of Planet Formation
  Observations of circumstellar disks around stars as a function of stellar
properties such as mass, metallicity, multiplicity, and age, provide
constraints on theories concerning the formation and evolution of planetary
systems. Utilizing ground- and space-based data from the far-UV to the
millimeter, astronomners can assess the amount, composition, and location of
circumstellar gas and dust as a function of time. We review primarily results
from the Spitzer Space Telescope, with reference to other ground- and
space-based observations. Comparing these results with those from exoplanet
search techniques, theoretical models, as well as the inferred history of our
solar system, helps us to assess whether planetary systems like our own, and
the potential for life that they represent, are common or rare in the Milky Way
galaxy.
