The Possible Tidal Demise of Kepler's First Planetary System

We present evidence of tidally-driven inspiral in the Kepler-1658(KOI-4)system, which consists of a giant planet(1.1R(J), 5.9M(J))orbiting an evolved host star(2.9R(circle dot), 1.5M circle dot). Using transit timing measurements from Kepler, Palomar/WIRC, and TESS, we show that the orbital period of Kepler-1658b appears to be decreasing at a rate <(P) over dot> = 131(-22)(+20)ms yr(-1), corresponding to an infall timescale P/<(P) over dot> approximate to 2.5 Myr. We consider other explanations for the data including line-of-sight acceleration and orbital precession, but find them to be implausible. The observed period derivative implies a tidal quality factor Q(star)' = 2.50(-0.62)(+0.85) x 10(4), in good agreement with theoretical predictions for inertial wave dissipation in subgiant stars. Additionally, while it probably cannot explain the entire inspiral rate, a small amount of planetary dissipation could naturally explain the deep optical eclipse observed for the planet via enhanced thermal emission. As the first evolved system with detected inspiral, Kepler-1658 is a new benchmark for understanding tidal physics at the end of the planetary life cycle.

Automated summary

We present evidence of tidally-driven inspiral in the Kepler-1658 system, which consists of a giant planet orbiting an evolved host star. The orbital period of the planet appears to be decreasing based on transit timing measurements, and we find other explanations for the data to be implausible. Tidal and planetary dissipation are considered as possible explanations for the observed phenomena. Kepler-1658 serves as a benchmark for understanding tidal physics at the end of the planetary life cycle.