Earth-Sized Exoplanets Have Circular Orbits and May be Habitable

First Posted: Jun 02, 2015 10:33 AM EDT

Which Earth-sized exoplanets are habitable? That's the question that scientists have asked one another for years as they continue the hunt for life on other planets. They've wondered whether the circular orbits seen in our own solar system are unusual rather than the norm, and whether that's why their hunt has remained fruitless for the time being. Now, though, they found that these circular orbits may actually be the norm for Earth-like planets.

In this latest study, the researchers examined 74 exoplanets located hundreds of light-years away. These exoplanets orbit a total of 28 stars, are about the size of Earth, and have circular trajectories that stand in stark contrast to more massive exoplanets.

"Twenty years ago, we only knew about our solar system, and everything was circular and so everyone expected circular orbits everywhere," said Vincent Van Eylen, one of the researchers, in a news release. "Then we started finding giant exoplanets, and we found suddenly a whole range of eccentricities, so there was an open question about whether this would also hold for smaller planets. We find that for small planets, circular is probably the norm."

The new findings are good news for the search of life elsewhere. If these planets maintain circular orbits, they would have a much more stable climate year-round. This would mean that it would be more likely for life to develop.

"If eccentric orbits are common for habitable planets, that would be quite a worry for life, because they would have such a large range of climate properties," said Van Eylen. "But what we find is, probably we don't have to worry too much because circular cases are fairly common."

The findings reveal that life may be possible on these smaller exoplanets. Now, the researchers hope to find out why larger planets have more eccentric orbits, and what causes these orbits in the first place.

The findings are published in The Astrophysical Journal.

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