Nasa's planet-hunting Kepler telescope has discovered more than 700 new worlds outside the solar system.
Scientists say the latest results push the number of planets discovered in the galaxy to about 1,700.
Just 20 years ago, astronomers had not found any planets circling stars other than the ones revolving around the sun.
"We almost doubled just today the number of planets known to humanity," Nasa planetary scientist Jack Lissauer said.
Nasa scientist Douglas Hudgins called the discovery a major step towards Kepler's ultimate goal: "finding Earth 2.0".
Astronomers used a new technique to come up with the largest single announcement of a batch of exoplanets - what planets outside our solar system are called.
All the new planets are in systems like ours where multiple planets circle a star.
The 715 planets were nearly all similar in size to Earth and four orbit their stars in "habitable zones" where conditions would support liquid water which is crucial for life to exist.
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