Velocities and transit times in the Kepler-88 system

Planet d is not detectable in the photometry, and long-baseline RVs are needed to ascertain its presence. A photodynamical model simultaneously optimized to fit the RVs and Kepler photometry yields the most precise planet masses and orbital properties yet for b and c: P_b_=10.91647{+/-}0.00014days, M_b_=9.5{+/-}1.2M_{Earth}_, P_c_=22.2649{+/-}0.0007days, and M_c=214.0{+/-}5.3M_{Earth}_. The photodynamical solution also finds that planets b and c have low eccentricites and low mutual inclination, are apsidally anti-aligned, and have conjunctions on the same hemisphere of the star.

Continued RV follow-up of systems with small planets will improve our understanding of the link between inner planetary system architectures and giant planets.