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74 Small Exoplanets With Circular Orbits Identified

Accepted submission by takyon at 2015-06-02 12:52:06
Science

Researchers from the Massachusetts Institute of Technology and Aarhus University have found that 74 small exoplanets orbit their stars in circular rather than eccentric patterns [mit.edu], suggesting that orbital regularity is common. The results [arxiv.org] could enhance the odds of finding Earth-sized exoplanets hospitable to life:

These 74 exoplanets, which orbit 28 stars, are about the size of Earth, and their circular trajectories stand in stark contrast to those of more massive exoplanets, some of which come extremely close to their stars before hurtling far out in highly eccentric, elongated orbits.

"Twenty years ago, we only knew about our solar system, and everything was circular and so everyone expected circular orbits everywhere," says Vincent Van Eylen, a visiting graduate student in MIT's Department of Physics. "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."

Ultimately, Van Eylen says that's good news in the search for life elsewhere. Among other requirements, for a planet to be habitable, it would have to be about the size of Earth — small and compact enough to be made of rock, not gas. If a small planet also maintained a circular orbit, it would be even more hospitable to life, as it would support a stable climate year-round. (In contrast, a planet with a more eccentric orbit might experience dramatic swings in climate as it orbited close in, then far out from its star.)

The team chose 28 stars with multiplanet systems that have been previously observed by the Kepler space observatory [wikipedia.org], and for which mass and radius had been determined using asteroseismology [wikipedia.org]. Every one of the 74 known exoplanets orbiting those 28 stars were found to maintain circular orbits.


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