On the structure and evolution of planets and their host stars $-$ effects of various heating mechanisms on the size of giant gas planets

TL;DR

This study investigates how various heating mechanisms, especially stellar irradiation and tidal effects, influence the size and evolution of giant gas planets, revealing a universal relation between radius and irradiated energy and estimating planetary mass loss over time.

Contribution

It introduces a unified relation between planetary radius and irradiated energy per gram, considers tidal heating effects, and develops a new method for age and initial mass estimation of giant planets.

Findings

A single radius-irradiation relation applies across all planetary mass intervals.

Planets with $l_-$ higher than 1100 $l_\oplus$ show increased radii likely due to molecular dissociation.

Highly irradiated gas giants lose about 5% of their mass every Gyr.

Abstract

It is already stated in the previous studies that the radius of the giant planets is affected by stellar irradiation. The confirmed relation between radius and incident flux depends on planetary mass intervals. In this study, we show that there is a single relation between radius and irradiated energy per gram per second ($l_-$), for all mass intervals. There is an extra increase in radius of planets if $l_-$ is higher than 1100 times energy received by the Earth ($l_\oplus$). This is likely due to dissociation of molecules. The tidal interaction as a heating mechanism is also considered and found that its maximum effect on the inflation of planets is about 15 per cent. We also compute age and heavy element abundances from the properties of host stars, given in the TEPCat catalogue (Southworth 2011). The metallicity given in the literature is as [Fe/H]. However, the most abundant element is oxygen, and there is a reverse relation between the observed abundances [Fe/H] and [O/Fe]. Therefore, we first compute [O/H] from [Fe/H] by using observed abundances, and then find heavy element abundance from [O/H]. We also develop a new method for age determination. Using the ages we find, we analyse variation of both radius and mass of the planets with respect to time, and estimate the initial mass of the planets from the relation we derive for the first time. According to our results, the highly irradiated gas giants lose 5 per cent of their mass in every 1 Gyr.