Adaptive Optics for Exoplanets: Science and Prospects

More than a thousand extrasolar planets are known, but almost all have been seen through ‘indirect’ techniques such as Doppler shifts of the parent star or the slight dimming as the planet occults its star. A handful have been directly images - spatially separated from their star - through the use of adaptive optics on large ground-based telescopes. Though few, these planets have been major steps in the post-copernican revolution, placing our solar system in a galactic context. For example, this enables high-resolution spectroscopy that can measure atmospheric composition of giant planets, or constraints on their orbits and interactions with the remainder of their solar system. I will review the science highlights of direct imaging. A new generation of instruments now online will be ten times more sensitive and vastly expand the set of directly imaged planets. The next step beyond that may involve applying similar techniques to space missions, such as the proposed WFIRST-AFTA 2.4m telescope, where the adaptive optics corrects not for atmospheric turbulence but for the complex wavefront produced by small imperfections in the telescope itself. Ultimately, such an instrument may lead to the first spectrum of at true Earth equivalent.