Evidence That the Occurrence Rate of Hot Jupiters around Sun-like Stars Decreases with Stellar Age

Abstract

We investigate how the occurrence rate of giant planets (minimum mass > 0.3 M Jup) around Sun-like stars depends on the age, mass, and metallicity of their host stars. We develop a hierarchical Bayesian framework to infer the number of planets per star (NPPS) as a function of both planetary and stellar parameters. The framework fully takes into account the uncertainties in the latter by utilizing the posterior samples for the stellar parameters obtained by fitting stellar isochrone models to the spectroscopic parameters, Gaia DR3 parallaxes, and 2MASS K s-band magnitudes adopting a certain bookkeeping prior. We apply the framework to 46 Doppler giants found around a sample of 382 Sun-like stars from the California Legacy Survey catalog that publishes spectroscopic parameters and search completeness for all the surveyed stars. We find evidence that the NPPS of hot Jupiters (orbital period P = 1–10 days) decreases roughly in the latter half of the main sequence over the timescale of  ( Gyr ) , while that of cold Jupiters (P = 1–10 yr) does not. Assuming that this decrease is real and caused by tidal orbital decay, the modified stellar tidal quality factor Q ⋆ ′ is implied to be  ( 10 6 ) for a Sun-like main-sequence star orbited by a Jupiter-mass planet with P ≈ 3 days.

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

“…Ultrahot Jupiters (UHJs), or giant planets with orbital periods of less than about 3 days, experience significant tidal effects that play a critical role in their long-term dynamical stability. Recent work has shown that the population of all hot Jupiter (P < 10 days) host stars is younger than the general population of either field stars or planet-hosting stars (Hamer & Schlaufman 2019), and two separate analyses have found lower UHJ occurrence rates around older host stars (Chen et al 2023;Miyazaki & Masuda 2023). All of this supports the idea that many giant, close-in planets quickly inspiral or are otherwise destroyed while their stars are still on the main sequence.…”

“…If WASP-12 is in fact evolved, that would leave no main-sequence stars known to host decaying planets, offering support to predictions that orbital decay is unlikely during the main sequence and is a feature of later stages of stellar life. This is, however, in tension with the independent observation that hot Jupiter host stars are younger than all planet hosts (Hamer & Schlaufman 2019;Chen et al 2023;Miyazaki & Masuda 2023) and that tidal decay does occur on the main sequence (Hamer & Schlaufman 2019). It is thus important to search more UHJs both on and off the main sequence for doomed worlds to see if this suggestive connection holds beyond a sample size of two planets.…”

The Apparent Tidal Decay of WASP-4 b Can Be Explained by the Rømer Effect

“…One of the key phenomena that has piqued the interest of astronomers is the tidal orbital decay of hot Jupiters, and as of now only WASP-12 b could be observationally confirmed to experience this effect [2][3][4]. However, there seems to be evidence for the occurrence rates of hot Jupiters in orbit around Sun-like stars to decrease with stellar age, as opposed to the occurrence rates of cold Jupiters, as found by Miyazaki and Masuda [5]. This is supported by the likely observation of planetary engulfment by a Sun-like star made by the Zwicky Transient Facility [6].…”

Relative Occurrence Rate between Hot and Cold Jupiters as an Indicator to Probe Planet Migration

“…Chen et al (2023) found that the discrepancy of η HJ between transit and RV surveys could be explained after accounting for the metallicity and age effect (and thus much less from the binarity effect). Such an effect is not yet seen to vary widely across stellar types (Miyazaki & Masuda 2023); hence, it may lead to a similar shift in the occurrence rate at different stellar…”