Full atmosphere-ocean model of a rotationally locked exoplanet

Artist's conception of the inner four planets of the Gliese 581 system and their host star.

Lynette Cook; NASA

The most common stars in our galaxy are dwarfs—smaller, reddish stars that emit far less light than our Sun. Because of this reduced output, the habitable zones of these stars are quite close-in. This means that any planets in the habitable zone will be close enough to become tidally locked, only showing a single face to the star, just as the Moon keeps just one side pointed at the Earth.

This led to the proposal that any watery worlds in the vicinity could form what's called an "Eyeball Earth." Directly under the local star, the light would be intense enough to melt a circular patch of water, while the rest of the planet would remain locked in a deep freeze.

Exoplanet climates go 3D

Now, a full model of the ocean and climate of a tidally locked planet suggests that the ice and oceans of these planets would be dynamic, distorting the dark pupil of the eyeball into something resembling a lobster. There's also good news and bad news for life on these watery planets. Although the analysis suggests a narrower habitable zone, more of the planet's surface would have the potential to support life.