New research suggests a staggering one in five stars most likely have an Earth-sized planet located in a habitable zone.
The data comes from the now-retired NASA Kepler telescope, a University of California, Berkeley, news release reported.
"What this means is, when you look up at the thousands of stars in the night sky, the nearest sun-like star with an Earth-size planet in its habitable zone is probably only 12 light years away and can be seen with the naked eye. That is amazing," UC Berkeley graduate student Erik Petigura, who led the analysis of the Kepler data, said.
"It's been nearly 20 years since the discovery of the first extrasolar planet around a normal star. Since then we have learned that most stars have planets of some size and that Earth-size planets are relatively common in close-in orbits that are too hot for life," Andrew Howard, a former UC Berkeley post-doctoral fellow who is now on the faculty of the Institute for Astronomy at the University of Hawaii, said. "With this result we've come home, in a sense, by showing that planets like our Earth are relatively common throughout the Milky Way galaxy."
The team warned not every planet within a hospitable zone would host life.
"Some may have thick atmospheres, making it so hot at the surface that DNA-like molecules would not survive. Others may have rocky surfaces that could harbor liquid water suitable for living organisms," Geoffrey Marcy, UC Berkeley professor of astronomy, said. "We don't know what range of planet types and their environments are suitable for life."
Many of the planets are believed to be rocky, just like Earth. Recently an Earth-sized rocky planet was discovered, but it was determined to be too hot to host life as we know it.
Out of the 150,000 stars Kepler photographed during its mission 3,000 planet candidates were reported. Most of these planets are believed to be inhospitable to life. The team found 10 planets that were Earth-sized and had a habitable orbit on their own.
The researchers used a highly-tested planet-finding algorithm to see how many Earth-sized planets in habitable zones were missed.
"What we're doing is taking a census of extrasolar planets, but we can't knock on every door. Only after injecting these fake planets and measuring how many we actually found, could we really pin down the number of real planets that we missed," Petigura said.
The formula showed 22 percent of all stars have planets in habitable zones.
"The primary goal of the Kepler mission was to answer the question, When you look up in the night sky, what fraction of the stars that you see have Earth-size planets at lukewarm temperatures so that water would not be frozen into ice or vaporized into steam, but remain a liquid, because liquid water is now understood to be the prerequisite for life," Marcy said. "Until now, no one knew exactly how common potentially habitable planets were around Sun-like stars in the galaxy."
