High precision, high cadence radial velocity monitoring over the past 8 years at the W. M. Keck Observatory reveals evidence for a third planet orbiting the nearby (4.69 pc) dM4 star GJ 876. The residuals of three-body Newtonian fits, which include GJ 876 and Jupiter mass companions b and c, show significant power at a periodicity of 1.9379 days. Self-consistently fitting the radial velocity data with a model that includes an additional body with this period significantly improves the quality of the fit. These four-body (three-planet) Newtonian fits find that the minimum mass of companion "d" is m sin i = 5.89 ± 0.54 M ⊕ and that its orbital period is 1.93776 (± 7 × 10 −5 ) days. Assuming coplanar orbits, an inclination of the GJ 876 planetary system to the plane of the sky of ∼ 50 • gives the best fit. This inclination yields a mass for companion d of m = 7.53 ± 0.70 M ⊕ , making it by far the lowest mass companion yet found around a main sequence star other than our Sun. Precise photometric observations at Fairborn 1 Based on observations obtained at the W.M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology.-2 -Observatory confirm low-level brightness variability in GJ 876 and provide the first explicit determination of the star's 96.7-day rotation period. Even higher precision short-term photometric measurements obtained at Las Campanas imply that planet d does not transit GJ 876.

We describe a 20-year survey carried out by the Lick-Carnegie Exoplanet Survey Team (LCES), using precision radial velocities from HIRES on the Keck-I telescope to find and characterize extrasolar planetary systems orbiting nearby F, G, K, and M dwarf stars. We provide here 60,949 precision radial velocities for 1,624 stars contained in that survey. We tabulate a list of 357 significant periodic signals that are of constant period and phase, and not coincident in period and/or phase with stellar activity indices. These signals are thus strongly suggestive of barycentric reflex motion of the star induced by one or more candidate exoplanets in Keplerian motion about the host star. Of these signals, 225 have already been published as planet claims, 60 are classified as significant unpublished planet candidates that await photometric follow-up to rule out activity-related causes, and 54 are also unpublished, but are classified as "significant" signals that require confirmation by additional data before rising to classification as planet candidates. Of particular interest is our detection of a candidate planet with M sin(i) = 3.8 M ⊕ , and P = 9.9 days orbiting Lalande 21185, the fourthclosest main sequence star to the Sun. For each of our exoplanetary candidate signals, we provide the period and semi-amplitude of the Keplerian orbital fit, and a likelihood ratio estimate of its statistical significance. We also tabulate 18 Keplerian-like signals that we classify as likely arising from stellar activity.