Astronomers say that one in six stars has an Earth-sized planet in a close orbit.
They gathered the information from Nasa's Kepler space observatory.
Kepler scientists now reckon there could be as many as 17 billion such planets in our galaxy.
They also announced 461 possible new planets, bringing the total number of planets found by the satellite to 2,740.
Kepler was launched into orbit in 2009 and looks at a fixed part of the sky, with a view of more than 150,000 stars
It looks for planets passing in front of stars, which it sees as tiny dips in light.