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A crucial clue in the search for extraterrestrial life is just around the corner, in cosmic terms.

Discovered in 2016, the planet called Proxima b circles our Sun’s nearest neighboring star, Proxima Centauri. Revealed by the telltale wobbles its gravitational tug elicits upon its star, this world is slightly more massive than Earth, and, like the Earth, resides in Proxima Centauri’s “habitable zone,” a circumstellar region in which warmth from starlight could conceivably allow liquid water to exist upon a rocky planet’s surface. Beyond that, not much more is known about this planet, and its similarities to our own Earthly situation may end there.

Proxima Centauri is a red dwarf, a ruddy stellar runt shining with only about a thousandth the brilliance of our far larger yellow star. Its planet’s orbit is correspondingly scaled-down, with a year that is only 11 days, not 365, placing it nearly 10 times closer-in than Mercury is to the Sun. And while starlight may be sufficient to sustain liquid water there, other effects of that close proximity—a far more luminous phase of the shrunken star’s youth, steady bombardment by powerful stellar winds and x-ray flares—could have long ago swept away the planet’s air, moisture and any possibility for surface life. Around red dwarfs, it seems, “habitable zones” and “danger zones” are much the same thing, and ever since Proxima b’s discovery scientists have been arguing about its prospects for life. The latest salvo in the debate emerged on July 24, in a paper from a group of researchers whose modeling suggested that, even protected by a potent magnetic field, an Earth-like atmosphere on Proxima b would still rapidly dissipate due to intense stellar radiation. Of course, no one is really convinced the case is closed.

“There are so many caveats, it’s really too early to answer the question” of Proxima b’s habitability, says the planet’s foremost discoverer, Guillem Anglada-Escudé, an astronomer at Queen Mary University of London. “It’s just a matter of philosophy and simulations right now. What we need is actual data.”

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