Skip to main content

Tens of billions of planets out there are like Earth, study finds

  • Astronomers used Kepler telescope data to extrapolate number of planets in Milky Way
  • 22% of sun-like stars have possibly habitable planets, research shows
  • Kepler has found 3,538 planet candidates to date

(CNN) -- Ever have one of those days where you just wanna be alone, maybe have the planet to yourself?

Well, based on sheer numbers, there may be a planet just for you.

Astronomers at the University of California-Berkeley and the University of Hawaii, using data from NASA's Kepler space telescope, estimate there are tens of billions of Earth-size, possibly habitable planets in our Milky Way galaxy.

Given that there just more than 7 billion of us on this planet, that means a planet for each of us with some spares for your picky neighbors. Or a vacation planet or two for you, maybe.

And the closest may be circling a star you can see if you look up into the heavens tonight.

"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, the leader of the team that analyzed data from the Kepler, said in a press release.

Lonely, young planet drifting in space without a star

To be sure, the astronomers haven't seen any of the planets themselves. They came to their conclusions like this:

Scientists announced in June 2013 that three planets orbiting star Gliese 667C could be habitable. This is an artist's impression of the view from one of those planets, looking toward the parent star in the center. The other two stars in the system are visible to the right. Scientists announced in June 2013 that three planets orbiting star Gliese 667C could be habitable. This is an artist's impression of the view from one of those planets, looking toward the parent star in the center. The other two stars in the system are visible to the right.
Where life might live beyond Earth
Photos: Where life might live beyond Earth Photos: Where life might live beyond Earth

The Kepler telescope photographed 150,000 of the 300 billion stars in the Milky Way every 30 minutes for four years. It looked for when orbiting planets passed between the camera and the star, causing a slight change in brightness of that star. Analyzing the data, the astronomers say, they found 3,000 planet candidates.

The astronomers narrowed that number by focusing on just 42,000 stars like our sun or a bit cooler. That brought the number of planets down to 603. But only 10 of those were about the size of Earth in the so-called "Goldilocks zone," just the right distance from the star where temperatures are suitable for life as we know it.

Diamonds may be produced on other planets

So how did they get a number of planets in the billions? By using a computer model with fake planets to test the validity of the algorithms used in the calculations.

"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 in the press release.

Using the data, the astronomers calculated that 22% of stars in the Milky Way similar to our sun have planets like Earth in their "Goldilocks zone." As there are about 20 billion stars similar to the sun in the galaxy, the possibilities add up quickly -- more than one for each of us Earthlings.

Stargazing in the desert: The magic of Namibia's night skies

The researchers do caution, though, that despite being in the habitable zone, a planet could still not be right to 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. We don't know what range of planet types and their environments are suitable for life," Geoffrey Marcy, UC Berkeley professor of astronomy, said in a press release.

But the study gives researchers a number to work with.

"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."

The new study is published in the Proceedings of the National Academy of Sciences and was discussed this week at the second Kepler Science Conference, being held at NASA's Ames Research Center in Moffett Field, California.

Also at the gathering, scientists announced the Kepler telescope has found 833 new candidate planets, including 10 that are of the right size and right distance from their stars to host life, adding to ones previously confirmed. That brings the official list to 3,538 planet candidates found using Kepler, according to a NASA press release. Of those, smaller Earth-sized planets are most common, NASA said.

Part of complete coverage on
updated 11:03 AM EDT, Wed April 9, 2014
Planetary nebula Abell 33 has taken on romantic proportions.
updated 11:55 AM EDT, Tue April 8, 2014
You can't see it happening on Earth, but space itself is stretching. Ever since the Big Bang happened 13.8 billion years ago, the universe has been getting bigger.
updated 4:59 PM EDT, Wed March 26, 2014
Scientists have added another celestial body to the short list of objects in our solar system that have rings around them.
updated 1:59 PM EDT, Thu March 27, 2014
Astronomers have discovered a dwarf planet that's even farther away than Pluto.
updated 7:59 AM EST, Fri February 28, 2014
Our galactic neighborhood just got a lot bigger. NASA announced the discovery of 715 new planets.
updated 10:37 AM EDT, Tue March 18, 2014
Scientists have made a breakthrough in understanding how our world as we know it came to be.
updated 3:27 PM EST, Tue February 25, 2014
From a sheep ranch in Western Australia comes the oldest slice of Earth we know.
updated 2:02 PM EST, Wed February 19, 2014
Cassiopeia A was a star more than eight times the mass of our sun before it exploded in the cataclysmic, fiery death astronomers call a supernova.
updated 5:07 PM EST, Mon February 10, 2014
Researchers have found clues that water could be flowing in the present, at least during warm seasons.
updated 11:02 AM EST, Sat February 15, 2014
The "jelly doughnut" rock that seemed to appear out of nowhere on Mars last month did not fall out of an extraterrestrial pastry box.
updated 10:56 PM EST, Thu February 6, 2014
It's a dot in the sky.
updated 2:44 AM EST, Thu February 13, 2014
Reports of Jade Rabbit's demise may have been premature.
updated 8:58 AM EST, Thu January 16, 2014
It's rare for astronomers to spot a planet in a star cluster. That's partly why a cluster called Messier 67 is so special: We now know that it has three planets orbiting stars.
updated 7:03 AM EST, Thu December 19, 2013
What do you need to map a billion stars? A billion-pixel camera certainly helps.
updated 2:50 PM EST, Tue December 10, 2013
NASA's rover Curiosity has now given scientists the strongest evidence to date that the environment on the Red Planet could have supported life billions of years ago.
updated 12:45 PM EST, Sat December 7, 2013
NASA's Cassini spacecraft has provided your multicolored space distraction of the day: images of a swirling, six-sided weather feature on the surface of Saturn.
updated 3:23 PM EST, Mon December 9, 2013
Imagine the delight at unwrapping your Christmas present in 2043 and discovering you've been gifted a trip around the Moon.
updated 5:06 PM EST, Tue December 10, 2013
A Dutch company says it is moving along with its plan to send four lucky Earthlings to colonize the Red Planet. The catch: They won't ever come back.
updated 12:11 PM EST, Tue November 19, 2013
You may have heard it before: billions of years ago Mars probably looked more like Earth does now, with clouds and oceans and a much thicker atmosphere.
updated 10:52 AM EST, Wed November 13, 2013
NASA has given the people of Earth a rare treat: A color mosaic that captures not only Saturn, but also the tiny dots of Earth and other planets in the background.
updated 12:39 PM EST, Tue November 5, 2013
Ever have one of those days where you just wanna be alone, maybe have the planet to yourself?