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Clouds may keep exoplanets cool

Even when close to their stars, other worlds could harbor liquid water

Clouds may keep Earth-sized exoplanets that sit close to their stars cool enough to have liquid water, as in this artist's conception.

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“Cloudy with a chance of life” is astronomers’ latest forecast for Earth-sized exoplanets, even if they tightly hug their stars.

Planets that sit too close to their stars should be sizzling hot and are tidally locked — one side of the planet always faces the star while the other side is always dark. But new climate simulations indicate that clouds can help mitigate the heat. On tidally locked Earth-sized planets that orbit red dwarfs, stars slightly smaller and cooler than the sun, clouds may reflect enough radiation to keep the temperature cool enough for liquid water. The clouds also should hold in enough radiation to warm the planet’s dark side.

The findings could double the number of potentially habitable Earth-sized planets around red dwarfs, Jun Yang of the University of Chicago and colleagues report in the July 10 Astrophysical Journal Letters.

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