# Orbital decay of short-period gas giants under evolving tides

## TL;DR

This paper introduces a semi-analytical model for the orbital decay of close-in gas giants that accounts for changes in planetary radius and dissipation parameters, revealing slower circularization timescales and implications for observed exoplanet eccentricities.

## Contribution

It presents a novel model incorporating evolving planetary properties during tidal interactions, improving understanding of orbital decay and eccentricity damping in gas giants.

## Key findings

- Eccentricity damping timescale increases by about an order of magnitude for inflated planets.
- Slower tidal circularization explains the prevalence of non-circularized close-in giants.
- Model constrains planetary interior properties through orbital evolution analysis.

## Abstract

The discovery of many giant planets in close-in orbits and the effect of planetary and stellar tides in their subsequent orbital decay have been extensively studied in the context of planetary formation and evolution theories. Planets orbiting close to their host stars undergo close encounters, atmospheric photoevaporation, orbital evolution, and tidal interactions. In many of these theoretical studies, it is assumed that the interior properties of gas giants remain static during orbital evolution. Here we present a model that allows for changes in the planetary radius as well as variations in the planetary and stellar dissipation parameters, caused by the planet's contraction and change of rotational rates from the strong tidal fields. In this semi-analytical model, giant planets experience a much slower tidal-induced circularization compared to models that do not consider these instantaneous changes. We predict that the eccentricity damping time-scale increases about an order of magnitude in the most extreme case for too inflated planets, large eccentricities, and when the planet's tidal properties are calculated according to its interior structural composition. This finding potentially has significant implications on interpreting the period-eccentricity distribution of known giant planets as it may naturally explain the large number of non-circularized, close period currently known. Additionally, this work may help to constrain some models of planetary interiors, and contribute to a better insight about how tides affect the orbital evolution of extrasolar systems.