A Planetary Companion to a Nearby M4 Dwarf, Gliese 876

Abstract

Doppler measurements of the M4 dwarf star Gliese 876 taken at both Lick and Keck Observatories reveal periodic, Keplerian velocity variations with a period of 61 days. The orbital fit implies that the companion has a mass of , an orbital eccentricity of , and a semimajor axis of M 2.1 M / sin i e 0.27 0.03 a 0.21 JUP AU. The planet is the first found around an M dwarf and was drawn from a survey of 24 such stars at Lick Observatory. It is the closest extrasolar planet yet found, providing opportunities for follow-up detection. The presence of a giant planet on a noncircular orbit, 0.2 AU from a 0.32 M , star, presents a challenge to planet formation theory. This planet detection around an M dwarf suggests that giant planets are numerous in the Galaxy.