General Milankovitch Cycles

The Earth is thought to have gone through at least one globally frozen, "snowball" state in the last billion years that it presumably exited after several million years of buildup of greenhouse gases when the ice-cover shut off the carbonate-silicate cycle. Extrasolar terrestrial planets with the capacity to host life might fall into similar snowball states. Here we show that if a terrestrial planet has a giant companion on a sufficiently eccentric orbit, it can undergo Milankovitch-like oscillations of eccentricity of great enough magnitude to melt out of a snowball state.