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Exoplanet Transit Timing Variations (TTVs) caused by gravitational forcesbetween planets can be used to determine planetary masses and orbitalparameters. Most of the observed TTVs are small and sinusoidal in time, leadingto degeneracies between the masses and orbital parameters. Here we report a TTVanalysis of Kepler-90g and Kepler-90h, which exhibit large TTVs up to 25 hours.With optimization, we find a unique solution which allows us to constrain allof the orbital parameters. The best fit masses for Kepler-90g and 90h are$15.0^{+0.9}_{-0.8}$ $M_{\bigoplus}$ (Earth mass) and$203^{+5}_{-5}M_{\bigoplus}$, respectively, with Kepler-90g having an unusuallylow apparent density of $0.15\pm 0.05\, {\rm g\,cm^{-3}}$. The uniqueness oforbital parameter solution enables a long-term dynamical integration, whichreveals that although their periods are close to 2:3 orbital resonance, theyare not locked in resonance, and the configuration is stable over billions ofyears. The dynamical history of the system suggests that planet interactionsare able to raise the eccentricities and break the resonant lock after theinitial formation.

Kepler-90: Giant transit-timing variations reveal a super-puff