Lobster-shaped extrasolar oceans

What the day side of a tidally locked exoplanet orbiting a red dwarf might look like, given atmospheric carbon dioxide levels similar to modern-day Earth. 

On the top frame, white represents ice while blue represents open water; on the bottom frame, colors represent surface air temperatures. 

The top image in each frame represents a computer model that does not take ocean heat flow into account; the bottom image in each frame does take such heat flow into account. 

Credit: Yongyun Hu

Yongyun Hu

Alien planets circling the most common stars in the universe may often have strange lobster-shaped oceans on their surfaces, researchers in China now say.

These findings suggest the habitable zones where life as we know it might dwell around these stars is smaller than previously thought, scientists added.

The most common type of star in the universe is the red dwarf. These stars, also known as M dwarfs, are small and faint, about one-fifth as massive as the sun and up to 50 times dimmer.

They make up to 70 percent of the stars in the cosmos, a vast number that potentially makes them valuable places to look for extraterrestrial life.

Indeed, recent findings from NASA's Kepler space observatory reveal that at least half of these stars host rocky planets that are one-half to four times the mass of Earth.

Artistic representation of five known potential habitable worlds including Gliese 581g. 

Credit: The Habitable Exoplanets Catalogue, PHL @ UPR Arecibo

Research into whether a distant planet might host life as we know it usually focuses on whether or not it has liquid water, since there is life virtually everywhere there is liquid water on Earth, even miles underground.

Scientists typically concentrate on habitable zones, also known as Goldilock zones—the area around a star where it is neither too hot nor too cold enough for a planet to possess liquid water on its surface.

The habitable zones around red dwarfs are close to such stars because of how dim they are, often closer than the distance Mercury orbits the sun.

Artist's impression of the planetary system around the red dwarf Gliese 581. Credit: ESA

This makes it relatively easy for astronomers to detect worlds in a red dwarf's habitable zone; since the orbits of these exoplanets are small, they complete their orbits quickly and often, and scientists can in principle readily detect the way these worlds dim the light of these stars by passing in front of them.

When a planet orbits a star very closely, the star's gravitational pull can force the world to become "tidally locked" to it.

When a planet is tidally locked to its star, it will always show the same side to its star just as the moon always shows the same side to Earth, so that the planet will have one permanent day side and one permanent night side.

More information: Hu and Yang detailed their findings online Dec. 30 in the journal Proceedings of the National Academy of Sciences: www.pnas.org/content/111/2/629.full