NASA — the U.S. space agency — said it found nearly 1,300 planets outside our solar system.
Nine of the planets are orbiting stars at the distance that can support life.
NASA said that the Kepler space telescope confirmed the existence of 1,284 planets. This result came from studying more than 4,000 possible planets identified by a statistical analysis.
Scientists said the research is important to help them find out whether there is life on other planets.
Paul Hertz is NASA’s director of astrophysics. He said, "this gives us hope that somewhere out there, around a star much like ours, we can eventually discover another Earth."
He said before the Kepler space telescope launched, scientists did not know whether exoplanets—those outside our solar system—were rare or common in the galaxy.
"We now know there could be more planets than stars," Hertz said.
He said the information brings humans a little closer to finding out whether they are alone in the universe.
To reach this number of planets, scientists looked at thousands of pieces of data. The researchers used a new statistical analysis method to study thousands of candidates in Kepler's database for traits that would establish them as planets.
Princeton University's Timothy Morton led the analysis. It involved watching a planet's brightness for changes that would mean it was orbiting its star, the way that Earth circles the sun.
The data gave scientists a "planethood probability percentage" to help the experts focus on candidates most likely to turn out to be actual planets.
But, with so many objects in space, what makes a planet, a planet?
The International Astronomical Union (IAU), approved the first scientific definition of a planet in August 2006. It says the object must have three things to be called a planet.
It must orbit its star. Second, it must be big enough that gravity shapes it into a ball. And third, the pull of that gravity must be strong enough to clear small objects out of the way of its orbit.
NASA said nearly 550 of the planets were “rocky planets,” somewhat like Earth, based on their size. Nine of those planets were orbiting their suns at the distance that would allow liquid water to pool.
That means, they have conditions that would make life possible. At least, the kind of life that exists here on Earth.
Natalie Batalha is Kepler mission scientist at NASA's Ames Research Center in California. She thinks there is life on other planets.
"Absolutely, no question," she said. "Why would we be the only ones?"
She used a line from the movie "Contact," that astronomer Carl Sagan was supposed to have said. If humans were the only life in the universe, it would be "an awful waste of space."
Recently, popular movies like "The Martian" and "Interstellar" have focused on finding new homes for humans in case we destroy Earth.
Batalha said she is focused on searching for life, not on finding new homes for humans.
"We have so many questions," she said. "Is DNA the only code that sustains life? How does life begin? Questions about the origin of life, why we're here."
That new number, 1,284 new planets, makes the idea that we are “alone in the universe” seem more and more unlikely.
I’m Anne Ball.
Marissa Melton wrote this story for VOA News. Anne Ball adapted it for Learning English. Hai Do was the editor.
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Words in This Story
statistical analysis – n. a mathematical process used to summarize data
trait – n. a quality that makes one person or thing different from another
sustain – v. to provide what is needed to exist
origin – n. the point or place where something begins or is created