Scientists from around the world have been scanning the heavens for other habitable planets to find an answer to the age-old question: Are we alone in the universe?
A study released Monday by a team of researchers from the University of Chicago and Northwestern University finds that the odds are good that we're not.
There may be 60 billion planets — double the number cited in earlier studies — in the Milky Way galaxy alone that could support life, according to the study.
In its search, NASA has so far found only 10 or so potentially habitable planets in their search for Earth-like planets, which the space agency describes as small, rocky planets orbiting sun-like stars.
The latest study found that cloud cover that could affect planet climate doubles the number of potentially habitable planets orbiting red dwarfs, which are the most common type of stars in the universe.
"Most of the planets in the Milky Way orbit red dwarfs," said Nicolas Cowan, a Northwestern researcher. "A thermostat that makes such planets more clement means we don't have to look as far to find a habitable planet."
The Northwestern-University of Chicago team based their findings on computer simulations of cloud behavior on alien planets.
Data collected from NASA's Kepler Telescope, which has been searching for potentially habitable planets orbiting other stars for the last four years, showed NASA scientists that each red dwarf could have one planet orbiting in its habitable zone, a relatively small area where an Earth-like planet could maintain liquid water on its surface.
The study that was released this week doubles that estimate.
"Clouds cause warming, and they cause cooling on Earth," said Dorian Abbot, an assistant professor in geophysical sciences at the University of Chicago. "They reflect sunlight to cool things off, and they absorb infrared radiation from the surface to make a greenhouse effect. That's part of what keeps the planet warm enough to sustain life."
Last week, a group of astronomers working with the European Southern Observatory reported the discovery of a solar system with three super-Earths that could possibly hold liquid water and thus support life.
The three potentially habitable planets are part of a system of at least six planets that orbit a star known as Gliese 667C, which is 22 light-years away from Earth in the constellation Scorpius or The Scorpion.
It was the first time that three planets have been found orbiting in a habitable zone in the same system.
Meanwhile, NASA in April reported that its Kepler Space Telescope found two other planets, 1,200 light years from earth, that are perfectly sized and positioned to potentially hold life.
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