Review Article

The “holy grail” is the imaging detection, and sub-
sequent spectroscopic study, of a terrestrial planet in
the habitable zone of a nearby star. Space-borne as-
trometry will provide a means of detecting and directly
measuring the masses and orbital configurations of ter-
restrial planets. One such mission on the near horizon
is the Space Interferometry Mission (SIM–Lite), which
will provide an astrometric precision of better than 1 μas
(Shao & Nemati 2008). Once Earth-like planets are iden-
tified, high-contrast imaging using techniques such as
adaptive optics and coronography can be brought to bear
to measure colors, and possibly even spectra, to search
for biosignatures. Ground-based imaging surveys are
making impressive strides, and planet searches are now
beginning with the NICI campaign (Artigau et al. 2008,
; Liu et al. 2009 in press) and in the near future with the
Giant Planet Imager (Macintosh et al. 2008), with the
goal of detecting Jupiters in wide orbits. The technology
developed for and proven by these surveys, and others
like them, will inform future imaging efforts from space,
such as the Terrestrial Planet Finder (Beichman et al.
2004).
In just 14 years conceptions of planets around other
stars have evolved from science fiction to a mature field
of scientific inquiry. The next decade holds much promise
as we progress toward the discoveries of solar systems like
our own around other stars.

John A. Johnson