  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.

Earth and Planetary Astrophysics