In “Most common stars are more life-friendly than thought” (New Scientist, 05 November 2011), Lisa Grossman reports:
SMALL and cool they may be, but red dwarfs, the most common kind of stars, are more likely to support life than we thought. Far-off icy planets that orbit these stars could still be warm enough to contain liquid water because of the way snow and ice absorb their near-infrared light.
Alien-hunting astronomers tend to look for planets in the “habitable zone”, the range of distances from a star where temperatures are balmy enough for water to be in liquid form but not so hot that it boils off.
Which some think to be a mistake. One astronomer has an ingenious theory for how red dwarfs might enable liquid water on far-off planets.
Ice and snow reflect 50 to 80 per cent of visible light so the ice on Earth bounces most sunlight back to space, and stays frozen. Compared with our sun, red dwarfs shine less in visible wavelengths, and brighter in the near-infrared, which ice and snow soak up. “If there’s ice or snow on the ground, more of the radiation that hits the surface will be absorbed,” Joshi says. “Which means that you’d expect it to be a lot hotter than it would be otherwise.”
This theory hasn’t changed the status of any known exoplanets, but it’s ingenious.
See also: Extraterrestrial civilizations: Have we tried looking for their city lights yet?
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