In a bit of cosmic irony, planets orbiting cooler stars may be more likely to remain ice-free than planets around hotter stars. According to a new study co-funded by the NASA Astrobiology Institute and published recently in Astrobiology, this is due to the interaction of a star’s light with ice and snow on the planet’s surface.

Stars emit different types of light. Hotter stars emit high-energy visible and ultraviolet light, and cooler stars give off infrared and near-infrared light, which has a much lower energy.

It seems logical that the warmth of terrestrial or rocky planets should depend on the amount of light they get from their stars, all other things being equal. But new climate model research led by Aomawa Shields, a doctoral student in the University of Washington astronomy department, has added a surprising new twist to the story: planets orbiting cool stars actually may be much warmer and less icy than their counterparts orbiting much hotter stars, even though they receive the same amount of light.

That’s because the ice absorbs much of the longer wavelength, near-infrared light predominantly emitted by these cooler stars. This is counter to what we experience on Earth, where ice and snow strongly reflect the visible light emitted by the Sun.