Scientists have found an Earth-sized planet only 4.3 light years away:
Bringing the search for another Earth about as close as it will ever get, a team of European astronomers was scheduled to announce on Wednesday that it had found a planet the same mass as Earth’s in Alpha Centauri, a triple star system that is the Sun’s closest neighbor, only 4.4 light-years away.
The planet is the lightest one ever found orbiting another star and — in the words of its discoverer, Xavier Dumusque, a graduate student at the Geneva Observatory — “it will surely be the closest one ever.”
It is presumably a rocky ball like our own, but it is not habitable. It circles Alpha Centauri B, a reddish orb about half as luminous as the Sun, every three days at a distance of only about four million miles, resulting in hellish surface temperatures of 1,200 degrees.
So this is not “Earth 2.0.” Yet.
Astronomers said the discovery raised the possibility that there were habitable Earthlike planets right next door and that methods and instruments were now precise enough to detect them.
“Very small planets are not rare,” said Mr. Dumusque, who is the lead author of a paper being published on Wednesday in Nature. “When you find one small planet, you find others.” He and his colleagues discussed the results on Tuesday in a news conference hosted by the European Southern Observatory in Garching, Germany.
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There are three stars in that system. Alpha Centauri A, which is slightly larger and brighter than the Sun, and Alpha Centauri B, slightly smaller, are close companions, circling each other and passing as close as nine billion miles every 80 years. They in turn are being circled at a much greater distance, some one trillion miles, by a dwarf star that is known as Proxima Centauri because it is slightly closer to the Earth, due to that trillion miles, than the other two.
The so-called habitable zone of Alpha Centauri B, where temperatures would be moderate enough for water and creatures like us, is about 65 million miles from the star, where a year would take 200 days or so, about the same as the orbit of Venus in our own system.
We keep getting closer and closer to the point where we’re actually going to find a planet in the Habitable Zone with evidence of the kind of atmosphere that can support life (and, yes, there are ways of detecting that even now). When that happens, the final confirmation that our world is not unique in the universe will have been received.
