A Physical Classification of Exoplanet Thermal Environments: Stellar Irradiation versus Tidal Heating

TL;DR

This paper introduces a physical framework to classify exoplanet thermal environments based on the relative contributions of stellar irradiation and tidal heating, using a dimensionless parameter applied to a large exoplanet sample.

Contribution

It develops a reproducible, physically motivated classification method centered on the parameter mbda, enabling analysis of thermal regimes dominated by different energy sources in exoplanets.

Findings

Most exoplanets are dominated by stellar irradiation.

A significant fraction of systems have tidal heating as the main energy source.

The boundary mbda=1 separates regimes with comparable flux contributions.

Abstract

In this study, we introduce a physical framework to analyse and classify the thermal regimes governed by tidal heating and stellar irradiation. Although all planetary systems are exposed to stellar radiation, this source is not always the dominant energy mechanism. This study is motivated by the lack of a physical framework that examines tidal heating in cases where this phenomenon dominates over stellar irradiation. We develop a reproducible physical approach that allows us to classify the relative contribution of both fluxes in a population of exoplanets, identifying the most relevant physical mechanisms that determine the thermal regime. We apply this method to a population of approximately 2000 exoplanets. This framework is centred on the dimensionless parameter \(\Lambda=F_{\mathrm{abs}}/F_{\mathrm{tide}}\), which quantifies the relative contribution of each flux. Our results show that most planetary thermal environments are dominated by \(F_{\mathrm{abs}}\), although there is a significant fraction of systems in which the tidal flux dominates. We identify a physical boundary at \(\Lambda=1\) that defines a regime in which both fluxes are comparable. We identify the semi-major axis \(a\) and the eccentricity \(e\) are the parameters that most influence the tidal flux. This framework provides a transparent and physically motivated tool for characterising planetary thermal environments and exploring the physical trends governing exoplanet populations.