How Common Are Habitable Planets? Astronomers Find Billions Similar To Earth
Astronomers have answered a key question about the nature of our universe: How many earth-like planets are there?
The number could be in the tens of billions, according to new research from the University of California, Berkeley, based on data beamed back from the Kepler space telescope. One co-author was so animated by the findings, he told The New York Times, "I'm feeling a little tingly."
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The news is a striking revelation in the search for life outside our solar system. Kepler, which NASA launched specifically to search for habitable planets, had seen nearly 3,000 planets roughly the size of earth pass in front of their suns as of earlier this year. The new study uses this data and estimates that for every five stars like the sun, a planet similar in size and orbit to the earth could be circling around one of them.
That adds up to about 40 billion earth-like planets in the Milky Way galaxy alone. And the nearest earth-size planet is so close to us — just 12 light-years — you don't need a telescope to see it.
"Until now, no one knew exactly how common potentially habitable planets were around sun-like stars in the galaxy," said Geoffrey Marcy, UC Berkeley professor of astronomy, in a statement. He helped write the article that appeared Monday in the journal Proceedings of the National Academy of Sciences.
He says "potentially." Just because an exoplanet (a planet outside our solar system) has roughly the same shape and amount of sunlight as our doesn't mean anybody's alive out there. The scientists don't even know what these planets are made of because they don't know their mass. They could be gaseous, or they could be Venus-like wastelands.
A 24-year-old UC Berkeley graduate student, Erik Petigura, led the analysis of the Kepler data and co-wrote the report along with Marcy and Andrew Howard, a professor at the Institute for Astronomy at the University of Hawaii.
They based their research on a few sets of assumptions. The first is what counts as potentially habitable. The habitable zone, they said, is a planet size between one and two times the size of earth and a distance from the sun that leaves it neither too hot nor too cold. Just the right distance allows for a temperature consistent with liquid water, a key ingredient of life, scientists say.
Scientists though, according to The Times, have identified examples of planets like ours that are just a little off. There's a planet called Kepler 78b, and last week researchers confirmed it has the same density of the earth; it's a big rock. Problem is, it's closer to its star than Mercury and completes its orbit in 8.5 hours. But, as Petigura said, "Nature knows how to make rocky earth-size planets," The Times reported.
For the Kepler mission, this is one of the most exciting postscrips since part of the telescope malfunctioned in 2012 and again earlier this year. But it gathered a lot of data since its 2009 launch, some of which has been made public for other astronomers to analyze.
"For NASA, this discovery is really important, because future missions will try to take an actual picture of a planet, and the size of the telescope they have to build depends on how close the nearest Earth-size planets are," Howard said. "An abundance of planets orbiting nearby stars simplifies such follow-up missions."
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