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An artist places us on the surface of Gliese 876 d, a planet in or near the habitable zone around a red dwarf star. (Inga Nielsen, Hamburg OBS., Gate To Nowhere)

Earth-Like Planets Could be Right Next Door

Astronomers estimate that billions of habitable planets are orbiting red dwarf stars. What would it be like to live there?

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For comparison, our sun is about halfway through its 10-billion-year lifespan; the simplest life on Earth developed about 3.8 billion years ago, and Homo sapiens barely more than 100,000 years ago. A red dwarf that was among the first stars that formed, nearly 13 billion years ago, could still be around today, and could theoretically be hosting a planet where life has existed for twice, maybe even three times as long as single-cell bacteria have existed on Earth.

“I’m very confident that within my lifetime—I’m 35 now—we will be able to find biosignatures of potentially habitable planets,” says Penn State’s Ravi kumar Kopparapu. His reported estimate, that as many as 61 percent of red dwarfs might have habitable planets, came from information about Venus and Mars extrapolated from our solar system’s history—that is, when water was still present on Venus before it evaporated and when the ice on Mars was liquid. Kopparapu calculated the sun’s brightness on each planet during these times and compared it to the brightness of red dwarfs. When he used this data to put limits on a habitable zone, he found it was larger than the zone Dressing used for her estimate.

Johnson, from Caltech, says speculating about what it’s like on a habitable planet orbiting a red dwarf is clearly an exercise that has just begun. “As for what’s [actually] going on on the surface of those planets, we don’t have the slightest clue, to be honest,” he says. Johnson said he’s still blown away by the thought that rocky, potentially habitable exoplanets are common. “I haven’t gotten used to that yet,” he says. “It’s not hunting anymore; it’s gathering. You just reach up into the sky and grab these things. They’re sitting right next door.”

“I would say it’s the golden age of exoplanet studies,” says Kopparapu. “The best studies are ahead, if we can get together and get missions going. Do we really want to know if we’re alone? I think we can find out, if we’re committed to it.”

Bruce Lieberman is a freelance science writer in Carlsbad, California. He writes about astrophysics, climate change, and other subjects.

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