Doomed Worlds. I. No New Evidence for Orbital Decay in a Long-term Survey of 43 Ultrahot Jupiters

Abstract

Ultrahot Jupiters (UHJs) are likely doomed by tidal forces to undergo orbital decay and eventual disruption by their stars, but the timescale over which this process unfolds is unknown. We present results from a long-term project to monitor UHJ transits. We recovered WASP-12 b’s orbital decay rate of P ̇ = − 29.8 ± 1.6 ms yr−1, in agreement with prior work. Five other systems initially had promising nonlinear transit ephemerides. However, a closer examination of two—WASP-19 b and CoRoT-2 b, both with prior tentative detections—revealed several independent errors with the literature timing data; after correction, neither planet shows signs of orbital decay. Meanwhile, a potential decreasing period for TrES-1 b, P ̇ = − 16 ± 5 ms yr−1, corresponds to a tidal quality factor Q ⋆ ′ = 160 and likely does not result from orbital decay if driven by dissipation within the host star. Nominal period increases in two systems, WASP-121 b and WASP-46 b, rest on a small handful of points. Only 1/43 planets (WASP-12 b) in our sample is experiencing detectable orbital decay. For nearly half (20/42), we can rule out P ̇ as high as observed for WASP-12 b. Thus, while many UHJs could still be experiencing rapid decay that we cannot yet detect, a sizable subpopulation of UHJs are decaying at least an order of magnitude more slowly than WASP-12 b. Our reanalysis of Kepler-1658 b with no new data finds that it remains a promising orbital decay candidate. Finally, we recommend that the scientific community take steps to avoid spurious detections through better management of the multi-decade-spanning data sets needed to search for and study planetary orbital decay.

Resonant and Ultra-short-period Planet Systems Are at Opposite Ends of the Exoplanet Age Distribution

“…The stellar tidal quality factor required for tidal dissipation inside a proto-USP planet's host star to explain our observation is similar to the measured value Q 2 10 5 ¢ » * for WASP-12 (Maciejewski et al 2016;Patra et al 2017;Yee et al 2020;Turner et al 2021), the only plausibly main-sequence star with a directly inferred Q ¢ * value. 7 However, WASP-12ʼs current Q ¢ * lies at the lower end of the range of Q ¢ * inferred for hot Jupiter host stars (e.g., Jackson et al 2008;Lanza et al 2011;Husnoo et al 2012;Adams et al 2024). In addition, a hot Jupiter system's orbital period, host-star structure, and planet mass have been theoretically shown to affect Q ¢ * (e.g., Weinberg et al 2012Weinberg et al , 2024.…”