Haven't seen Jason post anything about this .... I think this must be
the record for the lowest mass extrasolar planet orbiting a
main-sequence star. They are starting to push into terrestrial-mass
planet territory.


Title: A ~ 7.5 Earth-Mass Planet Orbiting the Nearby Star, GJ 876
Authors: E. J. Rivera, J. J. Lissauer, R. P. Butler, G. W. Marcy, S. S. Vogt, D. A. Fischer, T. M. Brown, G. Laughlin, G. W. Henry
Journal-ref: Astrophys.J. 634 (2005) 625

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 Earth masses and that
its orbital period is 1.93776 (+- 7x10^-5) days. Assuming coplanar
orbits, an inclination of the GJ 876 planetary system to the plane
of the sky of ~ 50 degrees gives the best fit. This inclination
yields a mass for companion d of m = 7.53 +- 0.70 Earth masses,
making it by far the lowest mass companion yet found around a main
sequence star other than our Sun. Precise photometric observations
at Fairborn 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.

URL: http://xxx.lanl.gov/abs/astro-ph?papernum=10508

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