The Last Gasp of Gas Giant Planet Formation: A Spitzer Study of the 5
  Myr-old Cluster NGC 2362
  (Abridged) We describe Spitzer IRAC and MIPS observations of the populous, 5
Myr-old open cluster NGC 2362. Early/intermediate-type confirmed/candidate
cluster members either have photospheric mid-IR emission or weak,
optically-thin infrared excess emission at < 24 microns consistent with debris
disks. Few late-type, solar/subsolar-mass stars have primordial disks. The disk
population around late-type stars is dominated by disks with inner holes
(canonical 'transition disks') and 'homologously depleted' disks. Both types of
disks represent an intermediate stage between primordial disks and debris
disks. Thus, we find that multiple paths for the primordial-to-debris disk
transition exist. Our results undermine standard arguments in favor of a ~ 0.01
Myr year timescale for the transition based on data from Taurus-Auriga and rule
out standard UV photoevaporation scenarios as the primary mechanism to explain
the transition. Combining our data with other Spitzer surveys, we investigate
the evolution of debris disks around high/intermediate-mass stars and
investigate timescales for giant planet formation. If the gas and dust in disks
evolve on similar timescales, the formation timescale for gas giant planets
surrounding early-type, high/intermediate-mass stars is likely 1--5 Myr. Most
solar/subsolar-mass stars detected by Spitzer have SEDs that indicate their
disks may be actively leaving the primordial disk phase. Thus, gas giant planet
formation may also occur by 5 Myr around solar/subsolar-mass stars as well.
