  We present an updated analysis of the GJ 876 planetary system based on an
augmented data set that incorporates 65 new high-precision radial velocities
obtained with the Keck telescope from 2001 to 2004. These new radial velocities
permit a more accurate characterization of the planet-planet interactions
exhibited by the system. Self-consistent three-body orbital fits (which
incorporate both the estimated instrumental uncertainties and 6 m/s Gaussian
stellar jitter) continue to show that GJ 876 b and GJ 876 c are participating
in a stable and symmetric 2:1 resonance condition in which the lowest order,
eccentricity type mean-motion resonance variables are all librating. The
planets are also locked in a secular resonance which causes them to librate
about apsidal alignment. The small libration widths of all three resonances
likely point to a dissipative history of differential migration for the two
planets in the system. (for full abstract see paper).
