Earth-sized planets in habitable zones are more common than previously thought

March 14, 2013

(Credit: Chester Harman)

The number of potentially habitable planets in our galaxy is greater than previously thought, according to a  new analysis by a Penn State researcher, and some of those planets are likely lurking around nearby stars.

“We now estimate that if we were to look at 10 of the nearest small stars we would find about four potentially habitable planets,” said Ravi Kopparapu, an Evan Pugh Professor in Penn State’s Department of Geosciences. “That is a conservative estimate,” he added. “There could be more.”

(Those additional ones might include habitable planets, if any, of the third-nearest star system, WISE J104915.57-531906, just discovered — see The closest star system found in a century).

A paper on Kopparapu’s findings, will be published in Astrophysical Journal Letters. In it, he recalculated the commonness of Earth-sized planets in the habitable zones of low-mass stars, also known as cool stars or M-dwarfs.

According to his findings, “The average distance to the nearest potentially habitable planet is about seven light years. That is about half the distance of previous estimates,” Kopparapu said. “There are about eight cool stars within 10 light-years, so conservatively, we should expect to find about three Earth-size planets in the habitable zones.”

Scientists focus on M-dwarfs for several reasons, he explained. The orbit of planets around M-dwarfs is very short, which allows scientists to gather data on a greater number of orbits in a shorter period of time than can be gathered on Sun-like stars, which have larger habitable zones. M-dwarfs are also more common than stars like the Earth’s Sun, which means more of them can be observed.

These new estimates are based on an updated model developed by Kopparapu and collaborators, using information on water and carbon dioxide absorption that was not available in 1993.

“I found that there are nearly three times as many Earth-sized planets in the habitable zones around these low mass stars as in previous estimates,” Kopparapu said. “This means Earth-sized planets are more common than we thought, and that is a good sign for detecting extraterrestrial life.”

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