Extrasolar Planets: Techniques, Results, and the Future

Abstract

To date, we have not obtained direct images of planets around other stars. However, the small-amplitude Keplerian motion of stars, presumably caused by the gravitational forces exerted them by planets, now provides information on their masses and orbits. The first extrasolar planetary system was found around a neutron star, the 6.2-millisecond pulsar PSR 1257+12 (Wolszczan & Frail 1992, Wolszczan 1998). Its three terrestrial-mass companions indicate the ubiquity and diversity of planetary systems. The leading model for the formation of the pulsar planets involves the post-supernova recapture of material, perhaps from a pre-existing stellar companion, into an accretion disk. The accumulation of dust grains into the pulsar planets may have occurred by processes similar to the formation of rocky planetary cores in our Solar System. The existence of pulsar planets suggests that planet formation is robust and depends little on specific disk properties, as long as adequate heavy elements are present (Wolszczan 1998).