Earth size planets in habitable zones are more common than previously thought

A Penn State researcher says that the number of Earth-size planets in habitable zones is greater than previously thought and a few of these planets may be orbiting nearby stars.
Ravi Kopparapu, a post-doctoral researcher in geosciences, described his findings in a paper accepted for publication in Astrophysical Journal Letters.
“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,” said Kopparapu. “That is a conservative estimate. There could be more.”
Kopparapu recalculated the number of Earth-size planets in the habitable zones of small stars, also known as cool stars or M-dwarfs. The habitable zone is defined as the area where conditions might potentially support life.
The orbit of planets around M-dwarfs is extremely short, which helps scientists obtain data on a greater number of orbits in a shorter period of time than can be amassed on Sun-like stars, which have bigger habitable zones. M-dwarfs are also more common than stars like our Sun.
“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.”
A recent study by researchers at the Harvard-Smithsonian Center for Astrophysics examined 3,987 M-dwarf stars to determine the number of Earth-sized planet candidates in cool stars’ habitable zones. Kopparapu discovered that the study’s findings, based on data from NASA’s Kepler satellite, didn’t take into consideration the most recent estimates for identifying whether planets are located within a habitable zone.
These newer estimates are based on an updated model created by Kopparapu and colleagues, utilizing information on water and carbon dioxide absorption that was not available to researchers at the Harvard-Smithsonian Center for Astrophysics in 1993. Kopparapu applied the newer estimates to the Harvard team’s study and discovered that there are additional planets in the newly determined habitable zones.