The Ice Coverage of Earth-like Planets Orbiting FGK Stars

TL;DR

This study uses climate simulations to estimate the distribution and frequency of surface ice on Earth-like planets orbiting FGK stars, revealing that most are ice-free and that ice distribution varies with stellar type and orbital dynamics.

Contribution

It introduces a comprehensive climate modeling approach to predict surface ice coverage patterns on habitable exoplanets, considering both static and dynamic orbital conditions.

Findings

Over 90% of simulated habitable planets are ice-free.

Ice belts are more common than caps on planets orbiting K and G stars.

Surface ice can cycle between poles and equator depending on orbital perturbations.

Abstract

The photometric and spectroscopic signatures of habitable planets orbiting FGK stars may be modulated by surface ice coverage. To estimate its frequency and locations, we simulated the climates of hypothetical planets with a 1D energy balance model and assumed that the planets possess properties similar to modern Earth (mass, geography, atmosphere). We first simulated planets with fixed rotational axes and circular orbits, finding that the vast majority (>90%) of planets with habitable surfaces are free of ice. For planets with partial ice coverage, the parameter space for ice caps (interannual ice located at the poles) is about as large as that for "ice belts" (interannual ice located at the equator), but belts only persist on land. We then performed simulations that mimicked perturbations from other planets by forcing sinusoidal orbital and rotational oscillations over a range of frequencies and amplitudes. We assume initially ice-free surfaces and set the initial eccentricity distribution to mirror known exoplanets, while the initial obliquity distribution matches planet formation predictions, ie favoring 90 degrees. For these dynamic cases, we find again that ~90% of habitable planets are free of surface ice for a range of assumptions for ice's albedo. Planets orbiting F dwarfs are three times as likely to have ice caps than belts, but for planets orbiting K and G dwarfs ice belts are twice as likely as caps. In some cases, a planet's surface ice can cycle between the equatorial and polar regions. Future direct imaging surveys of habitable planets may be able to test these predictions.