Milky Way Home To 17 Billion Earth-Sized Planets, Astronomers Announce

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Artist's illustration of planets discovered by the Kepler spacecraft. | CFA

There are at least 17 billion Earth-sized planets in our galaxy, scientists have announced.

In fact there could be many, many more.

Astronomers have announced that at least 17 percent of stars - roughly one in six - host a planet which is roughly the same size as Earth, in a close orbit similar to our own.

There are about 100 billion stars in our galaxy - meaning 17 billion Earth-a-likes is a good ballpark figure.

But it's not just Earth-sized planets which could be capable of supporting life. Larger rocky worlds orbiting their suns at larger differences could also be a home to strange life forms, meaning the total number of worlds on which organic life could evolve could be even greater.

"These kind of rocky objects are everywhere," said Francois Fressin, a team member at the Harvard-Smithsonian Center for Astrophysics.

The findings were announced at the 221st meeting of the American Astronomical Society.

The team analysed data by the Kepler Space Telescope, which is able to detect alien planets by changes in the brightness of stars as they pass in front of its surface relative to Earth.

The telescope launched in 2009 and has since found more than 2,700 potential planets orbiting 150,000 stars.

Of these about 461 are the same size as Earth, in a similar orbit - and 10 are in the zone where liquid water could exist.

By simulating how the telescope works, the researchers found that it is at least 90 percent accurate - leading them to round up to the rough 17 billion figure.

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