Are there 300 million more Earths out there?

(Nanowerk News) From philosophers and astronomers to the child gazing up at the cosmos in wonder, the question remains unanswered: How many planets beyond our solar system known as exoplanets could host life? We’re getting closer to the answer.

How big is space?

According to a paper accepted for publication in The Astronomical Journal ("The Occurrence of Rocky Habitable Zone Planets Around Solar-Like Stars from Kepler Data"), worlds with similar conditions to Earth could have a rocky planet able to support liquid water on its surface.
In collaboration with colleagues from around the world, NASA scientists examined data gathered from the Kepler Mission’s space telescope that monitored about 150 000 stars. NASA’s planet-hunting mission successfully identified more than 4 000 exoplanets that could be candidates. They also used valuable data from the European Space Agency’s Gaia mission whose satellite has measured the position and brightness of 1 billion stars.
NASA estimates that there are about 100 to 400 billion stars in our Milky Way. A recent study (The Astronomical Journal, "Searching the Entirety of Kepler Data. II. Occurrence Rate Estimates for FGK Stars") estimates there may be up to 6 billion Earth-like planets in our galaxy.
“This is the science result we’ve all been waiting for,” co-author Natalie M. Batalha, an astronomer at the University of California, Santa Cruz, told ‘National Geographic’. Early estimates indicated that 7 % of Sun-like stars hosted a world similar to Earth’s. That number is now closer to 50 %, and possibly even more. “It’s higher than I thought. I was always saying to the public, one in four, one in five—this result is quite a pleasant surprise,” Prof. Batalha added. “Every other sunlike star is likely, on average, to have a potentially habitable planet.”
The researchers searched for stars similar to the Sun in age and temperature. They also searched for exoplanets with a similar radius to Earth’s and chose those that were most likely rocky. They also considered each planet’s distance from its star. Thanks to Gaia data, the team was able to take temperature into consideration for the very first time when calculating all these factors.

Can we end interstellar loneliness?

Some of these exoplanets could be fairly close to us. At least 4 are potentially within 30 light years of the Sun, with the closest probably about 20 light years at most from Earth.
“Kepler already told us there were billions of planets, but now we know a good chunk of those planets might be rocky and habitable,” lead author Steve Bryson, a researcher at NASA’s Ames Research Center in California’s Silicon Valley, commented. “Though this result is far from a final value, and water on a planet’s surface is only one of many factors to support life, it’s extremely exciting that we calculated these worlds are this common with such high confidence and precision.”
“To me, this result is an example of how much we’ve been able to discover just with that small glimpse beyond our solar system,” noted Bryson. “What we see is that our galaxy is a fascinating one, with fascinating worlds, and some that may not be too different from our own.”
Source: Cordis
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