investigate the atmospheres of extrasolar planets like Earth will succeed. A critical step along the way is a better understanding of the dusty disks surrounding stars, analogous to zodiacal dust found near Earth. Reflected diffuse exozodiacal light from these disks can make detection of the faint light from small Earth-like planets difficult. It is, therefore, important to quantify the prevalence and character of these dusty “debris” disks, and the period 2010-2015 will see the completion of ground-based mid-infrared interferometric instrumentation designed to study these phenomena.

It is also important to understand planetary systems in the process of formation to enrich and complement observations of the mature exoplanets. ALMA will revolutionize the imaging of protoplanetary disks at millimeter and submillimeter wavelengths and reveal important clues to the formation and evolution of their constituent planets. JWST and ground-based infrared telescopes equipped with adaptive optics to remove the twinkling due to Earth’s atmosphere will provide spatially resolved multiwavelength images and spectra of light scattered from these disks with spatial resolution comparable to that of ALMA.

JWST, with its superb mid-infrared capability, will also use imaging and spectroscopy transit techniques to study the atmospheres of exoplanets, a science capability that has been amply demonstrated by the currently operating Spitzer Space Telescope. JWST will be a premier tool for studying planets orbiting stars that are smaller and cooler than the Sun. Also promising are improved techniques on the ground for direct imaging of planets using adaptive optics. New instrumentation is required as well as significant amounts of observing time (for example, on the Gemini telescopes and the privately operated facilities accessible through NSF’s Telescope System Instrumentation Program). The proposed GSMTs could also play a crucial role in direct imaging studies with instruments suitably designed for this type of work.

In addition, enhancements to NASA Suborbital and Explorer programs could provide testbeds for the development of occulter techniques such as the use of star shades and coronagraphy, which are both immature, and technology development of astrometry and interferometry from space, so as to set the stage for an ambitious direct-detection mission in the 2020s. The scientific contributions and technology development in these various areas are described in detail elsewhere.9

The culmination of the quest for nearby, habitable planets is a dedicated space mission. The committee concluded that it is too early to determine what the design

9

ExoPlanet Task Force of the Astronomy and Astrophysics Advisory Committee, Worlds Beyond: A Strategy for the Detection and Characterization of Exoplanets, National Science Foundation, Washington, D.C., 2008, available at http://www.nsf.gov/mps/ast/exoptf.jsp; Jet Propulsion Laboratory, Exoplanet Community Report (P.R. Lawson, W.A. Traub, and S.C. Unwin, eds.), JPL Publication 09-3, Pasadena, Calif., 2009.



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