Cloud Behavior Indicates 60 Billion Planets In Milky Way Could Be Habitable: Study

An artist's rendering image released to Reuters on October 19, 2009 shows an exoplanet 6 times the Earth-size circulating around its low-mass host star at a distance equal to 1/20th of the Earth-Sun distance.

A new study on how clouds affect temperatures on alien planets has expanded the number of exoplanets, or planets outside our solar system, which are believed to be capable of supporting life, according to a study published in the Astrophysical Journal Letters.

The study was conducted by a team of scientists from the University of Chicago and Northwestern University using a 3D model they created to analyze how clouds would affect temperatures on these outlier planets.  

“Clouds cause warming, and they cause cooling on Earth," Dorian Abbot, an assistant professor in geophysical sciences at the University of Chicago, and one of the study’s authors, told The Christian Science Monitor. "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."

Too far from a star and any water on an exoplanet would freeze while too much closeness to a star would evaporate any water present on a planet.

By this measure, the results showed that 60 billion planets could be habitable, as each one of them is situated at just the right distance from its star to preserve water in a liquid form -- a requirement for life to survive. This finding doubles the number of planets that scientists previously believed could possibly support life.

A Los Angeles Times report pointed out that the increase in number is because scientists have now taken into account the role of clouds in altering the temperature of a planet that was previously considered too close to its star to support life.

Researchers believe, the Times report said, that the part of the planet that directly faces its star will have a thick cloud shielding it, which will reflect heat and light back to the source, thereby preventing the planet from getting too warm.

"Normally you would expect a planet to be hotter on the day side than on the night side," Abbot told the Los Angeles Times. "But a planet with a weather pattern like this will be colder on the day side than on the night side. If you see that reversal, we were right."