Worlds beyond: A strategy for the detection and characterization of exoplanets. Executive summary of a report of the ExoPlanet Task Force Astronomy and Astrophysics Advisory Committee Washington, DC June 23, 2008.

WE STAND ON A GREAT DIVIDE in the detection and study of exoplanets. On one side of this divide are the hundreds of known massive exoplanets, with measured densities and atmospheric temperatures for a handful of the hottest exoplanets. On the other side of the divide lies the possibility, as yet unrealized, of detecting and characterizing a true Earth analogue—an Earth-like planet (a planet of one Earth mass or Earth radius orbiting a Sun-like star at a distance of roughly one astronomical unit). This ExoPlanet Task Force Report describes how to bridge the divide. The recommendations emphasize immediate investment in technology and space mission development that will lead to discovering and characterizing Earth analogues. We recognize that setting a goal of detecting planets like Earth sets the bar high. It is important that the program target such objects if we are to determine whether the conditions we find on our own world are a common outcome of planetary evolution. The only example of a habitable world we have is our own one-Earth-mass planet; and indeed our nearest neighbor, Venus, is nearly the same mass but uninhabitable by virtue of closer proximity to the Sun. Searching for planets, for example, five times the mass of Earth is easier. But should they turn out to lack habitable atmospheres, we would not know whether this is by chance or whether it is a systematic effect of the higher mass. The connection of