Gravity-Darkened Seasons: Insolation Around Rapid Rotators

TL;DR

This paper models how rapid stellar rotation causes gravity-darkening, leading to significant variations in a planet's insolation and UV exposure depending on orbital inclination, with implications for planetary climate and habitability.

Contribution

It introduces a model of insolation variations caused by gravity-darkening in rapid rotators, highlighting the impact on planetary temperature and radiation exposure.

Findings

Planet equilibrium temperature can vary by up to 15%.

UV radiation exposure can change by approximately 80%.

Gravity-darkening effects are significant for planets orbiting rapid rotators.

Abstract

I model the effect of rapid stellar rotation on a planet's insolation. Fast-rotating stars have induced pole-to-equator temperature gradients (known as gravity-darkening) of up to several thousand Kelvin that affect the star's luminosity and peak emission wavelength as a function of latitude. When orbiting such a star, a planet's annual insolation can strongly vary depending on its orbit inclination. Specifically, inclined orbits result in temporary exposure to the star's hotter poles. I find that gravity-darkening can drive changes in a planet's equilibrium temperature of up to $\sim15\%$ due to increased irradiance near the stellar poles. This effect can also vary a planet's exposure to UV radiation by up to $\sim80\%$ throughout its orbit as it is exposed to an irradiance spectrum corresponding to different stellar effective temperatures over time.