The formation and detection of extrasolar habitable worlds

Abstract
With well over a hundred Jupiter-class planets now discovered, speculation on the abundance of Earth-like planets in the cosmos will soon give way to efforts to detect and characterize them. The formation of terrestrial planets-rocky bodies like Earth, Venus, and Mars-appears to be a natural consequence of the rapid growth of lunar- to Mars sized "embryos" after the disruptive era of giant planet formation. Then, gravitational perturbations by Jupiter-mass planets may elongate the orbits of the embryos, causing the bodies to collide and grow. Architectures not too dissimilar to our own inner solar system may be obtained after roughly 100 million years, for a giant planet in the region around 5 AU or so from a Sun-like star. Discovery of terrestrial planets will likely come first from spaceborne telescopes that sense the dimming of starlight as planets pass directly in front of their parent stars ("transit"), or for distant planetary systems, via the so-called microlensing technique. To discover habitable planets will require direct detection of the light of the planet, so that spectra may be taken to identify atmospheric carbon dioxide, water vapor, methane and oxygen. Such an undertaking will require large telescopic systems deployed in space.