Images of exoplanets orbiting

Images of exoplanets orbiting nearby stars have been recorded by two groups. Though hundreds of exoplanets have been found by various nonimaging means, there had previously been no unambiguous images of objects smaller than brown dwarfs actually orbiting stars. Now a group led by Christian Marois of the Hertzberg Institute of Astrophysics in Victoria, British Columbia, has used adaptive optics at two large telescopes on Hawaii's Mauna Kea to capture IR images of three Jovian planets orbiting a luminous young star (see figure). Because the star is only about 60 million years old, the planets' residual heat of formation provides enough IR glow for imaging. One doesn't expect reflected starlight to be adequate for imaging at visible wavelengths. Nonetheless, a group led by Paul Kalas of the University of California, Berkeley, has used a Hubble Space Telescope camera with a coronographic occulting disk to acquire visible images of a planet orbiting Fomalhaut, one of the brightest young stars in the night sky. The planet's brightness in the visible is tentatively attributed to starlight reflected off a circumplanetary disk much wider than Saturn's. All four newly discovered planets orbit their stars at distances at least 20 times greater than Earth's distance from the Sun. Exoplanets with such large orbital radii cannot be detected by the usual nonimaging search techniques. Direct imaging has the further advantage of promising to reveal photometric and spectroscopic information about a planet's makeup. (C. Marois et al., Science 322, 1348, 2008; P. Kalas et al., Science 322, 1345, 2008.) — Bertram Schwarzschild