Doubt Raised Over Discovery of New 'Habitable' Planet

(Oct. 13) -- Astronomers grabbed headlines last month when they announced they had discovered an Earth-like planet that could theoretically support alien life, but now at least one scientist is questioning the finding.

"We cannot confirm the presence of the announced planet Gliese 581g," Francesco Pepe of the Geneva Observatory in Switzerland told Astrobiology Magazine in an e-mail.

Astronomer Steve Vogt of the University of California, Santa Cruz, described Gliese 581g as a rocky planet that fits the profile needed to contain water, the basis for life. He said he stands by his work.

Gliese 581g is an extrasolar planet, which means that it can't simply be seen with a telescope in the way Mars or Venus can. Instead, scientists try to deduce the presence of the planet from its gravitational pull on its star, which affects the star's position in the sky.

Unfortunately, not all the changes in a star's position necessarily arise from the presence of a planet, so planet-hunters have to be able to filter out the impact of other phenomena in order to discover new worlds.

It could be that what seemed like a breakthrough in the hunt for a habitable world is something other than a planet.

"Simulations on the real data have shown that the probability that such a signal is just produced 'by chance' out of the noise is not negligible, of the order of several percents," Pepe told the magazine.

Gliese 581g excited scientists because of its apparent similarity to Earth. Vogt and his team described a world that had a diameter about 1.2 to 1.4 times that of the earth.

The planet appeared to be a rocky world, rather than a gaseous planet like Jupiter. Its orbit, around a star 20 light years away from our solar system, suggested that temperatures on some parts of the planet would allow water to exist as a liquid.

Vogt and his team based their study on 11 years' worth of observations, and they are certainly not giving up yet.

In an e-mail to AOL News, Vogt said that he would examine Pepe's work once it has been published in a peer-reviewed journal.

"They must publish their data, analysis and conclusions in a peer-reviewed archival scientific journal for all the world and history to see," Vogt said. "I stand by our data and analysis."

Media coverage of Gliese 581g may have overstated Vogt's case, making a possibility sound like a sure thing, Ray Jayawardhana, an astronomer at the University of Toronto, told Astrobiology Magazine.

"I would say the detection was less than comfortably secure, even in the original Vogt et al. paper -- the paper was carefully worded, as opposed to what was in some media reports," Jayawardhana said.

The hunt for alien life and earth-like worlds has gone on for centuries. Near the turn of the 20th century, American astronomer W.H. Pickering believed that he saw signs of vegetation on the moon and oases on Mars.

As astronauts and satellites explored the solar system, it seemed unlikely that we would find life on other planets in our system, and scientists have looked further afield.

This means using more advanced and experimental techniques. According to B. Scott Gaudi, an assistant professor of astronomy at Ohio State University, these techniques inevitably mean that there will be scientific debate about results -- exactly what he sees taking place in the Gliese 581g discussion.

"This is more or less part of the process," Gaudi told AOL News. "It's part of the scientific method."

Still, Vogt seems confident that his work will stand the test of this scientific debate.

"In 15 years of exoplanet hunting, with over hundreds of planets detected by our team, we have yet to publish a single false claim, retraction, or erratum," Vogt told AOL News. "We are doing our level best to keep it that way."