Two-Star Earth-like Planets Could Host Life

Artist impression of the Kepler-35 system. Lior Taylor/NASA

A new model shows that Earth-sized planets orbiting two stars could retain water for a really long time, suggesting that they could be suitable for hosting life. Earth-size exoplanets might be sporting a variety of different environments and not just deserts like Star Wars’ Tatooine.

In a paper, published in Nature Communications, researchers Max Popp and Sigfried Eggl used data from the Kepler mission to create a realistic simulation of an exoplanet around two stars, also known as circumbinary planets.

"Our research is motivated by the fact that searching for potentially habitable planets requires a lot of effort, so it is good to know in advance where to look," Eggl, from NASA’s Jet Propulsion Laboratory, said in a statement. "We show that it's worth targeting double-star systems."

The research uses as a model of the Kepler-35 system. The system has two yellow stars only slightly less massive than our Sun. They are orbited by a gas giant named Kepler-35b. For the study, the scientists ignored the gas giant and pretended a water-rich Earth-size planet was orbiting the two stars with a period of between 341 and 380 days.

The amount of stellar light a planet like this would receive is expected to vary wildly depending on its place in the orbit and distance from the stars. Slight differences could lead a planet to be a moist greenhouse or a snowball world, but an Earth-like regime is also allowed.

A planet at the edge of the habitable zone would have strong variation in global temperatures over the course of the year, even up to a few degrees. A planet there would have little water vapor in its atmosphere, which would make it similar to deserts with temperatures swinging wildly from day to night.  

Within the habitable zone, but closer to the two stars, the planet would be able to keep a stable temperature.

"This means that double-star systems of the type studied here are excellent candidates to host habitable planets, despite the large variations in the amount of starlight hypothetical planets in such a system would receive," added Popp, from Princeton University in New Jersey, and the Max Planck Institute of Meteorology.

The scientists also discovered that such a planet would have fewer clouds in the sky than Earth. Making these worlds ideal location to stare wistfully at a double sunset.


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