Transit timing variations of Kepler-90g and h

Most of the observed TTVs are small and sinusoidal in time, leading to degeneracies between the masses and orbital parameters. Here we report a TTV analysis of Kepler-90g and Kepler-90h, which exhibit large TTVs up to 25hr.

With optimization, we find a unique solution that allows us to constrain all of the orbital parameters. The best-fit masses for Kepler-90g and 90h are 15.0_-0.8_^+0.9^M{Earth} (Earth mass) and 203_-5_^+5^M_{Earth}, respectively, with Kepler-90g having an unusually low apparent density of 0.15{+/-}0.05g/cm^3^. The uniqueness of orbital parameter solution enables a long-term dynamical integration, which reveals that although their periods are close to 2:3 orbital resonance, they are not locked in resonance, and the configuration is stable over billions of years.