Reinflation of Warm and Hot Jupiters

Abstract

Understanding the anomalous radii of many transiting hot gas giant planets is a fundamental problem of planetary science. Recent detections of re-inflated warm Jupiters orbiting post-main-sequence stars and the re-inflation of hot Jupiters while their host stars evolve on the main-sequence may help constrain models for the anomalous radii of hot Jupiters. In this work, we present evolution models studying the re-inflation of gas giants to determine how varying the depth and intensity of deposited heating affects both main-sequence re-inflation of hot Jupiters and post-main-sequence re-inflation of warm Jupiters. We find that deeper heating is required to re-inflate hot Jupiters than is needed to suppress their cooling, and that the timescale of re-inflation decreases with increasing heating rate and depth. We find a strong degeneracy between heating rate and depth, with either strong shallow heating or weak deep heating providing an explanation for main-sequence re-inflation of hot Jupiters. This degeneracy between heating rate and depth can be broken in the case of post-main-sequence re-inflation of warm Jupiters, as the inflation must be rapid to occur within post-main-sequence evolution timescales. We also show that the dependence of heating rate on incident stellar flux inferred from the sample of hot Jupiters can explain re-inflation of both warm and hot Jupiters. TESS will obtain a large sample of warm Jupiters orbiting post-main-sequence stars, which will help to constrain the mechanism(s) causing the anomalous radii of gas giant planets.

NLTT5306B: an inflated, weakly irradiated brown dwarf

“…However, brown dwarfs have a significantly higher internal temperature than exoplanets which may have an effect on how the radius of a brown dwarf reacts to heating. The current configuration of the binary has been in place for ∼700 Myr, considerably shorter than the 5-10 Gyr reinflation time-scales in Komacek et al (2020) for heat deposited anywhere but the core of the planet. This would suggest if reinflation is the mechanism that inflated the radius of NLTT5306B, then the heat is being deposited right to the centre of the brown dwarf.…”

“…There has been some discussion regarding Hot Jupiters and whether they may be re-inflated due to the evolution of their host star (e.g. Lopez & Fortney 2016;Komacek et al 2020). For these exoplanets, it has been determined that there needs to be a slow deposition of heat into the core over a long period of time, as merely slowing the rate of contraction for the exoplanet is not sufficient to cause the large radii seen for some exoplanets (Thorngren, Gao & Fortney 2019;Komacek et al 2020).…”

“…Lopez & Fortney 2016;Komacek et al 2020). For these exoplanets, it has been determined that there needs to be a slow deposition of heat into the core over a long period of time, as merely slowing the rate of contraction for the exoplanet is not sufficient to cause the large radii seen for some exoplanets (Thorngren, Gao & Fortney 2019;Komacek et al 2020). NLTT5306B has an equilibrium temperature of 920 K if albedo is neglected; just on the limit of what is presumed to be possible as exoplanets with T eq <1000 K are not found to be inflated.…”

TOI-481 b and TOI-892 b: Two Long-period Hot Jupiters from the Transiting Exoplanet Survey Satellite

“…In this context it is important to note that TOI-481 is in the final stages of the main-sequence evolution and has started to receive increased levels of irradiation during the last gigayear of evolution. Its non-inflated radius can be linked with a shallow level deposition of the stellar energy into the planet interior during main-sequence evolution as argued by Komacek et al (2020), which is not enough to re-inflate the planet even at temperatures higher than 1000 K. If warm Jupiters are efficiently re-inflated during post-main-sequence evolution, as some recent studies have proposed (Grunblatt et al 2016(Grunblatt et al , 2017Jones et al 2018), then some other mechanism should operate to allow the deposition of energy deeper in the planet interior.…”

Ariel planetary interiors White Paper

“…A common denominator from all these studies is that the inflation of hot-Jupiters is caused by the intense stellar irradiation that these planets receive, and therefore changes in the stellar irradiation either due to stellar evolution (e.g., [39,40,70]) or to the planet migration-that changes their semi major axis and the received Flux-(e.g., [12,101]), can cause a change in the inflation rate of planets, reflecting the planet history.…”