DETECTION OF EXTRASOLAR GIANT PLANETS

Abstract

▪ Abstract Eight extrasolar planet candidates have now been identified, all revealed by Keplerian Doppler shifts in their host stars. The masses (m sin i) lie between 0.5 and 7 M JUP, and the semimajor axes are less than 2.1 astronomical units (AU). Doppler detectability favors high masses and small orbits, and improvements will render Saturn masses detectable within a few years. The substellar mass function (dN/dM) for companions is roughly flat from 70 down to 10 M JUP, but it exhibits a sharp increase for masses below 5 M JUP. For three of these companions (47 UMa, ρ Crb, and 55 Cnc), their circular orbits must be primordial (not tidally induced), indicating formation in a disk, as presumed for Solar System planets. Eccentric orbits may be explained by gravitational perturbations, either by companion stars, other planets, or disk resonances. The detections imply that ∼6% of solar-type stars have giant planets within 2 AU. The small orbits (a < 2 AU) imply that the planets formed either in situ, without the benefit of ice grains, or suffered inward migration. Orbital decay within 1 Myr in disks appears inevitable and may shape the planet mass distribution. The observed stability of spectral line shapes suggests that nonradial stellar oscillations do not affect the planet detections.