Kepler Space Telescope finds Earth-size, potentially habitable planets are common
Video: One in every five sunlike stars is orbited by a potentially habitable planet, according to a new analysis of observations by NASA’s Kepler Space Telescope. Video courtesy of Petigura/UC Berkeley; Howard/UH-Manoa; Marcy/UC Berkeley; Illumina Studies, Emeryville, Calif.
Roughly one in every five sunlike stars is orbited by a potentially habitable, Earth-size planet, meaning that the universe has abundant real estate that could be congenial to life, according to a new analysis of observations by NASA’s Kepler Space Telescope.
Our Milky Way galaxy alone could harbor tens of billions of rocky worlds where water might be liquid at the surface, according to the report, which was published Monday in the Proceedings of the National Academy of Sciences and discussed at a news conference in California.
If the estimate is correct, the nearest ocean planet might be just 12 light-years away, which, though extremely distant for all practical purposes (such as sending a robotic space probe), is just around the corner in our galactic neighborhood.
“When you look up at the stars in the night sky, how many of them have a planet like the Earth?” asked Erik Petigura, a graduate student at the University of California at Berkeley and the lead author of the paper. “We’re able to start answering this question.”
The best estimate is 22 percent of stars like our own, with an error margin of plus or minus 8 percent.
“Earth-sized planets having the temperature of a cup of tea are common around sunlike stars,” said planet hunter Geoff Marcy, a Berkeley astronomer and a co-author of the study. He said the finding “represents one great leap toward the possibility of life, including intelligent life, in the universe.”
Kepler, launched in 2009, is no longer able to search for “exoplanets” — outside our solar system — because it has been unable to point with precision after the failure of a steering mechanism this year. But the telescope amassed more than three years of observations before going on the blink. Kepler mission scientist Natalie Batalha said there’s still another full year of data to rummage through.
The telescope’s original mission was to obtain an estimate of the percentage of stars with potentially habitable planets, and this latest analysis comes close to meeting that goal. This is still an extrapolation of data, and is not the same thing as taking a careful census of these Earth-size planets directly, said Sara Seager, an astrophysicist at the Massachusetts Institute of Technology who was not directly involved in the new analysis.
“Earth-size” doesn’t necessarily mean “Earth-like,” she noted. But she said this result will boost efforts to build new telescopes that could potentially obtain direct imagery of one of these extremely distant worlds.
“Earth-sized planets are not rare, so we’ll know we’ll have stuff to look at,” Seager said. “It's reassuring for us."
Jill Tarter, a pioneer in SETI, the search for extraterrestrial intelligence, said in an e-mail: “We haven’t yet found Earth 2.0, but these statistics suggest that it should be forthcoming, and soon. When we can point to Earth 2.0 in the sky, it will seem completely natural to ask ‘Does anybody live there?’ and ‘Can we go there?’ I think Earth 2.0 will concretize SETI as nothing else has.”
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Kepler Space Telescope finds Earth-size, potentially habitable planets are commonContinuedKepler studied 150,000 stars in a small patch of the sky in the constellation Cygnus. The planets surrounding distant stars can’t be seen directly, because their faint, reflected light is swamped by the much brighter starlight. Thus Kepler looked for the periodic dimming of a star, which could be the signal of a planet passing across the star’s face.
The Kepler team has found amid Kepler’s data 10 “candidate” planets that, while not yet confirmed, appear to be roughly one to two times the mass of the Earth and orbiting at “Goldilocks” distances, neither too close nor too far from the stars.
The scientists extrapolated in two ways. They know that most planets are unlikely to be in orbits that, just by chance, cause them to pass in front of the face of the star as seen from Kepler. That’s a 1-in-100 longshot. For every planet seen, multiply by 100.
The scientists also knew that some planets would remain difficult to detect due to natural fluctuations in starlight — the “noise” in the signal. They found a way to test the accuracy of the algorithms for detecting planets by inserting 40,000 “synthetic” planets into the computer programs and seeing how many would be accurately retrieved by those programs.
The analysis doesn’t prove that any of these “habitable zone” planets actually resembles Earth. The report states only that they are roughly the size of our planet and aren’t too close or too far from the star for water — if it is present — to be liquid at the surface.
Moreover, being in a star’s habitable zone does not ensure that life will actually spring forth. Scientists have limited understanding of the origin of life on Earth. There could also be other constraints on life originating on another world. The Earth has a number of features that are amenable to life and that might not be common, including a nearly circular orbit, a large companion moon and tectonic activity that recycles the planet’s carbon.
Even with this new analysis, extraterrestrial life remains conjectural. There are no known examples of it, which is why skeptics sometimes say that exobiology is a science without a subject. But since the first extrasolar planet was discovered in 1995, hundreds more have been confirmed.
Kepler has found 3,538 candidate planets, meaning planets that need to be confirmed by further observation, said Jason Rowe, a research scientist at the SETI Institute, at the news conference Monday at which Kepler results were announced.
Of those, 647 are Earth-size, 104 are in the star’s habitable zone and 10 meet both criteria. But William Borucki, the principle investigator for Kepler, noted that some of larger planets in the habitable zone might have moons amenable to life.
“All of those 104, I think, are very interesting planets,” Borucki said.
He said that roughly 70 percent of stars appear to have at least one planet. If the new estimate is correct, by his calculation there should be about 25 billion Earth-size planets in habitable zones in our galaxy.
“Those numbers are pretty soft. We have a lot of corrections to make before we have really definitive numbers,” Borucki said.
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Comments
4:38 AM GMT+0800
As a sci fi fan, I've always believed that intelligent life must exist elsewhere in the Universe. However, the article only focuses on one characteristic, i.e., a planet being in the 'goldilocks' zone of it's orbited star. However, there are many, many other factors that allowed life to progress on Earth, including:
1. a molten iron core that generates a strong magnetic field, deflecting harmful radiation
2. the existence of super planets in the same system that blocked the worst of debris.
3. the existence of a moon that blocked some debris, but also generate tides
4. active tectonic plates that recycle minerals.
5. the composition of the planet (water, oxygen, carbon, hydrogen, other elements and minerals)
6. a precise axis tilt that provides seasonal changes.
plus many other factors.
As planetary research progresses, it's becoming more and more clear that Earth is very special in its capacity to harbor life capable of evolving intelligence. I think there must be other planets with intelligent life. I hope someday we will be ready to meet them. However, to assert that habital planets are 'common' is a bit strong I think.
1. a molten iron core that generates a strong magnetic field, deflecting harmful radiation
2. the existence of super planets in the same system that blocked the worst of debris.
3. the existence of a moon that blocked some debris, but also generate tides
4. active tectonic plates that recycle minerals.
5. the composition of the planet (water, oxygen, carbon, hydrogen, other elements and minerals)
6. a precise axis tilt that provides seasonal changes.
plus many other factors.
As planetary research progresses, it's becoming more and more clear that Earth is very special in its capacity to harbor life capable of evolving intelligence. I think there must be other planets with intelligent life. I hope someday we will be ready to meet them. However, to assert that habital planets are 'common' is a bit strong I think.
4:47 AM GMT+0800
wolfeja...I've been a life long sci-fi fan too. There may be many planets with simple life. But, I agree with you that planets that can form intelligent, thus fragile life, are rare and delicate. The molten iron core and its magnetic field being critical as you say.
4:47 AM GMT+0800
Excellent commentary - I agree it is too strong. On the other hand, I think biology is also finding that life may be a bit tougher than we first thought. It is hard to tell what that means for habitability.
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1. a molten iron core that generates a strong magnetic field, deflecting harmful radiation
2. the existence of super planets in the same system that blocked the worst of debris.
3. the existence of a moon that blocked some debris, but also generate tides
4. active tectonic plates that recycle minerals.
5. the composition of the planet (water, oxygen, carbon, hydrogen, other elements and minerals)
6. a precise axis tilt that provides seasonal changes.
plus many other factors.
As planetary research progresses, it's becoming more and more clear that Earth is very special in its capacity to harbor life capable of evolving intelligence. I think there must be other planets with intelligent life. I hope someday we will be ready to meet them. However, to assert that habital planets are 'common' is a bit strong I think.