New Constraints on Gliese 876 — Exemplar of Mean-Motion Resonance
GJ876 is one of the most dynamically rich and well-characterized planetary systems. The nearby M-dwarf hosts four known planets, the outer three of which are trapped in a 4:2:1 Laplace mean-motion resonance. I recently conducted a reanalysis of the system using six years of new radial velocity data from four instruments. I performed a complex dynamical RV fit to the system; the procedure included a computationally efficient Wisdom-Holman N-body symplectic integrator and a Gaussian Process (GP) regression model to account for correlated stellar noise. Our new analysis suggests that the system might be in a low energy, quasi-periodic double apsidal corotation resonance, as opposed to the more vigorously chaotic configuration suggested by past work. This surprising result will be examined in greater detail in a subsequent study of the primordial migration processes responsible for the assembly of the resonant chain.