Exoplanet transit-timing variations (TTVs) caused by gravitational forces between planets can be used to determine planetary masses and orbital parameters. 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 25 hr. 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 M _⊕ (Earth mass) and , respectively, with Kepler-90g having an unusually low apparent density of 0.15 0.05 g 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. The dynamical history of the system suggests that planet interactions are able to raise the eccentricities and break the resonant lock after the initial formation.

由行星之间的引力引起的系外行星凌日时间变化 (TTV) 可用于确定行星质量和轨道参数。大多数观测到的 TTV 很小，并且在时间上呈正弦曲线，导致质量和轨道参数之间存在简并性。在这里，我们报告了 Kepler-90g 和 Kepler-90h 的 TTV 分析，它们展示了长达 25 小时的大型 TTV。通过优化，我们找到了一个独特的解决方案，使我们能够约束所有轨道参数。Kepler-90g 和 90h 的最佳质量分别是 M _⊕（地球质量）和，Kepler-90g 的表观密度异常低，为 0.15 0.05 g cm ^-3. 轨道参数解的独特性使得长期动力学积分成为可能，这表明虽然它们的周期接近 2:3 轨道共振，但它们并未锁定共振，并且构型稳定数十亿年。该系统的动力学历史表明，行星相互作用能够在初始形成后提高离心率并打破共振锁定。