TECH
05/11/2013 05:58 GMT | Updated 23/01/2014 10:52 GMT

Milky Way Galaxy May Hold 20 Billion Earth-Like Planets

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There may be up to 20 billion habitable planets in our galaxy, scientists have said.

About one in five stars which researchers have been able to study for evidence of planets so far has an Earth-sized world within the so-called 'habitable zone'.

The conclusion? Planets like ours are a "relatively common" occurrence in the universe.

The 'habitable zone' is described as a distance far enough from the sun to have a surface temperature which could support liquid water.

So far Nasa's Kepler space telescope, which has scoured the skies for planets since its launch in 2009, has found evidence of these Earth-like planets in orbit around 22% of stars.

The team admits that not all of these planets will be able to hold life - variables such as their size, density and the age of the star all affect how possible it is that life could be sustained.

Photo galleryArtists' Conceptions Of Extrasolar Planets See Gallery

"Some may have thick atmospheres, making it so hot at the surface that DNA-like molecules would not survive. Others may have rocky surfaces that could harbor liquid water suitable for living organisms," said Geoffrey Marcy, UC Berkeley professor of astronomy.

"We don't know what range of planet types and their environments are suitable for life."

But if their rough calculation holds true across the galaxy, the nearest Earth-like planet capable of sustaining life might be just 12 light years away.

"Human beings have been looking at the stars for thousands of years," study researcher Erik Petigura, a graduate student at the University of California, Berkeley, told Space.com.

"How many of those stars have planets that are in some way like Earth? We're very excited today to start to answer that question.

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About 1,000 alien worlds have been confirmed so far using data from Kepler and other telescopes. While the Kepler telescope is now at the end of its mission after suffering damage to its rotator wheels, there is still mountains of data from the satellite with which scientists can find more planets.