'Earth-like' planets three times more than thought

The number of Earth-sized and potentially habitable planets is three times higher than previously believed, an Indian-origin scientist has claimed.
Some of those planets are likely lurking around nearby stars, according to Ravi Kopparapu, a post-doctoral researcher in geosciences in the Penn State University.
"We now estimate that if we were to look at 10 of the nearest small stars we would find about four potentially habitable planets, give or take," Kopparapu said.
"That is a conservative estimate. There could be more," Kopparapu added.
Kopparapu 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 in a statement.

"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," he said.
The work follows up on a recent study by researchers at the Harvard-Smithsonian Center for Astrophysics which analysed 3,987 M-dwarf stars to calculate the number of Earth-sized planet candidates in cool stars' habitable zones - a region around a star where rocky planets are capable of sustaining liquid water and therefore life.

Kopparapu noticed that its findings, based on data from NASA's Kepler satellite, didn't reflect the most recent estimates for determining whether planets fall within a habitable zone.
These newer 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 used our new habitable zone calculations and 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," said Kopparapu.

The study was published in the journal Astrophysical Journal Letters.