Scientists find most Earthlike planet yet

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David Charbonneau, an astronomer at the Harvard-Smithsonian Center for Astrophysics who was not involved in the study, said the new finding is an “absolutely fantastic discovery.”

“It means there probably are many more such planets out there,” Charbonneau said in a telephone interview. Whether Gliese 581 C harbors life is still unknown, but “it satisfies for the first time a key requirement.”

Charbonneau also praised the team’s technical skills. “The wobble induced on the star by each of these planets is really tiny — it’s just a few meters a second. That means their measurement precision is exquisite,” he said.

David Latham, another astronomer at Harvard-Smithsonian CfA, echoed other scientists’ praise of the discovery but said the next step is to find a similar world where the orbit of the habitable planet carries it between Earth and its parent star. This will allow scientists to observe it using the transit technique, whereby the small dimming starlight caused by the planet’s passage across the face of its sun can be used to calculate its size.

Only then can scientists determine for certain whether the world is rocky or covered by water, Latham said.

Alan Boss, a planetary theorist at the Carnegie Institution of Washington in Washington D.C., said the new planet’s potential for liquid water made it “fascinating." Gliese 581 C “is the closest planet to another Earth that has been found to date. I hope the SETI folks are listening,” Boss said.

Seth Shostak, a senior astronomer at the SETI institute, said the Gliese 581 system has in fact been looked at twice before for signs of intelligent life. The first time was in 1995 using the Parks Radio Telescope in Australia; the second time was using the Greenbank Radio Telescope in West Virgina. Both times revealed nothing.

“It has been looked at twice, but that doesn’t mean we shouldn’t look at it again,” Shostak said. “And indeed we should because this is the best candidate the solar planet guys have come up with yet.”

Shostak said he was “jazzed” by the discovery. “This is pointing to something that in the past has only been an assumption, namely that Earth-sized worlds are not rare,” he said. “We know of only two [planets in the habitable zone]. We know this one and we know our own. But two is better than one.”

Shostak said the Gliese 581 system might be looked at again when the new Allen Telescope Array begins operations this summer.

“You could say it’s going to the head of the class,” he said.

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