WASHINGTON — Our galaxy is looking far more crowded and hospitable. NASA on Wednesday confirmed a bonanza of 715 newly discovered planets outside our solar system.
Scientists using the planet-hunting Kepler telescope pushed the number of planets discovered in the galaxy to about 1,700. Twenty years ago, astronomers had not found any planets circling stars other than the ones revolving around our sun.
"We almost doubled just today the number of planets known to humanity," NASA planetary scientist Jack Lissauer said during a Wednesday teleconference, calling it "the big mother lode."
Astronomers used a new confirmation technique to come up with the largest single announcement of a batch of exoplanets — what planets outside our solar system are called.
While Wednesday's announcement was about big numbers, it also was about implications for life behind those big numbers.
All of the new planets are in systems like ours where multiple planets circle a star. The 715 planets came from looking at just 305 stars. They were nearly all in size closer to Earth than to gigantic Jupiter.
And four of the new exoplanets orbit their stars in "habitable zones" where it is not too hot and not too cold for liquid water, which is crucial for life to exist.
Douglas Hudgins, NASA's exoplanet exploration program scientist, called Wednesday's announcement a major step toward Kepler's ultimate goal: "finding Earth 2.0."
It's a big step in finding not just other Earths but "the possibility of life elsewhere," said Lisa Kaltenegger, a Harvard and Max Planck Institute astronomer who wasn't part of the discovery team.
The four new habitable zone planets are all at least twice as big as Earth, so that makes them more likely to be gas planets instead of rocky ones like Earth — and less likely to harbor life.
So far, Kepler has found nine exoplanets in habitable zones, NASA said. Astronomers expect to find more when they look at all four years of data collected by the now-crippled Kepler; so far, they have looked at two years' worth.
Planets in the habitable zones are likely to be farther out from their stars because it is hot close in. And planets farther out take more time orbiting, so Kepler had to wait longer to see them again.