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Scientists estimate billions of habitable planets in Milky Way

March 28, 2012|By Deborah Netburn
  • This artist's impression shows a sunset seen from the super-Earth Gliese 667 Cc.
This artist's impression shows a sunset seen from the super-Earth… (ESO / L. Calcada )

Looking for a new planet to colonize? A team of European astronomers says you've got options -- billions of them.

Using results from the High Accuracy Radical Velocity Planet Searcher (HARPS) at the European Southern Observatory, the scientists say there are likely tens of billions of planets in the Milky Way galaxy alone that may be able to sustain life.

They estimate that one hundred of those planets are in the sun's immediate neighborhood -- which in space-speak is 30 light years away.

The generally accepted (though perhaps shortsighted) definition of a planet that can sustain life is one that has a mass between one and 10 times that of Earth, as well as a rocky surface, and the ability to sustain liquid water -- meaning the planet's surface temperature is neither too hot that water would evaporate nor too cold that it would freeze.

Although there are no planets that meet those criteria in our own solar system, the report suggests that they are common around other stars.

For this study, scientists focused exclusively on finding planets orbiting red dwarf stars, which are fainter and cooler than our sun, but which make up 80% of the stars in the Milky Way.

After surveying a carefully chosen sample of red dwarf stars over a period of six years, the team concluded that 40% of all red dwarf stars have rocky planets roughly the same size of the Earth located in the "habitable zone."

"Because red dwarfs are so common -- there are 160 billion of them in the Milky way -- this leads us to the astonishing result that there are tens of billions of these planets in our galaxy alone," Xavier Bonfils, the French astronomer who led the research team, said in a statement.

There is a caveat, however, and it's kind of a big one.

Since red dwarfs are cooler than our sun, a planet would have to be much closer to the star than Earth is to the sun] in order for the planet's surface to be warm enough to sustain liquid water.

And as team member Stephane Udry of Geneva University notes, the planet may then be all the more susceptible to the "stellar eruptions or flares, which may bathe the planet in X-rays or ultraviolet radiation, and which may make life there less likely."

Which leads us to conclude that there is no place like home.

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Original source: Scientists estimate billions of habitable planets in Milky Way

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