  The study of planets beyond the solar system and the search for other
habitable planets and life is just beginning. Ground-based (radial velocity and
transits) and space-based surveys (transits and astrometry) will identify
planets spanning a wide range of size and orbital location, from Earth-sized
objects within 1 AU to giant planets beyond 5 AU, orbiting stars as near as a
few parsec and as far as a kiloparsec. After this initial reconnaissance, the
next generation of space observatories will directly detect photons from
planets in the habitable zones of nearby stars. The synergistic combination of
measurements of mass from astrometry and radial velocity, of radius and
composition from transits, and the wealth of information from the direct
detection of visible and mid-IR photons will create a rich field of comparative
planetology. Information on proto-planetary and debris disks will complete our
understanding of the evolution of habitable environments from the earliest
stages of planet-formation through to the transport into the inner solar system
of the volatiles necessary for life.
  The suite of missions necessary to carry out the search for nearby, habitable
planets and life requires a ``Great Observatories'' program for planet finding
(SIM PlanetQuest, Terrestrial Planet Finder-Coronagraph, and Terrestrial Planet
Finder-Interferometer/Darwin), analogous to the highly successful ``Great
Observatories Program'' for astrophysics. With these new Great Observatories,
plus the James Webb Space Telescope, we will extend planetology far beyond the
solar system, and possibly even begin the new field of comparative evolutionary
biology with the discovery of life itself in different astronomical settings.
