Unearthing another earth
Physicists’ data suggest the possibility of life beyond our planet
UT Arlington physics Associate Professor Manfred Cuntz and a team of scientists recently took one giant step toward answering a question that has tantalized stargazers for centuries. Is anyone out there?
Using a climate model and a model for the evolution of Earth-like planets, they demonstrated habitable conditions on Gliese 581d in the constellation Libra, 20 light years away.
Last spring a European Space Agency team working in Chile discovered two “Super Earths” far removed from our solar system. Labeled Gliese 581c and Gliese 581d, they differ from most planets recently found outside the solar system and are more similar to Saturn or Jupiter.
The scientists thought that Gliese 581c—the smaller of the two planets at five times the size of Earth—contained an atmosphere that would enable something to survive. Turns out that’s not the case, a fact established by Dr. Cuntz’s mathematical analysis.
“Gliese 581c is just too hot for life to exist,” he said. “Owing to the fact that the planet is too close to its host star, it is just like Venus. It is simply too close to its sun.”
Along with the research team, headed by Werner von Bloh at the Potsdam Institute for Climate Impact Research in Germany, Cuntz prepared a report for Astronomy and Astrophysics, one of the most prestigious journals in astrophysics. The report shows that it is the larger, colder Gliese 581d that may have a life support system in place. Eight times the size of Earth, it sits in a “tidally locked” state. That is, when moving along its orbit, it doesn’t spin on its axis like Earth does.
Cuntz has a lifelong interest in planets in their earliest stages. “I’ve always wanted to be a witness of newly formed planets.”
And life on those planets?
“Typically, scientists like the idea of life on planets because that opens the possibility of more interesting studies.”
Cuntz and his UT Arlington colleagues, physics Professor Zdzislaw Musielak and graduate student Jason Eberle, were aiming their studies at planets around many different stars long before Gliese 581c proved it was not another Earth.
The trick to finding the zone on a planet where life has a chance to survive and evolve is to think like Goldilocks: not too hot, not too cold, but just right. Orbiting at 23 million miles from its parent star, Gliese 581d is far too cold for liquid water unless there is extra heating. But Gliese 581d is believed to have copious amounts of greenhouse gases. Although a bad sign on Earth, this could make the planet livable.
Cuntz conducted extensive data verifications while other research team members studied climatology. They studied how long Gliese 581d had been around (perhaps 2 billion years, but maybe as long as Earth, or about 4.5 billion years), where its orbit takes it and what its surface climate is like.
Gliese 581c had proved unlivable because greenhouse gases keep temperatures intolerably hot, largely because the planet is three times closer to its parent star than Gliese 581d. But that same carbon dioxide provides thermal insulation for Gliese 581d, stopping the temperature from being extremely cold.
Consequently, life has a chance to begin—if it hasn’t already. Harvard-Smithsonian astrophysicist Dimitar Sasselov agreed in a piece in The New York Times that greenhouse gases are positive in this case.
“I would trust that result,” he said of Cuntz’s work, “because I’m getting the same numbers.”
How good is the data? Good enough to turn once-unrealistic missions into explorations with funding now under way.
Jane Platt with Jet Propulsion Laboratories in California said plans have begun for NASA’s Terrestrial Planet Finder and the European Space Agency’s Darwin to study terrestrial planets beyond Earth’s solar system. The mission will attempt to detect biomarkers, molecules that indicate if living organisms are or were present in the atmospheres of planets like those around Gliese 581d.
Steven Dick, NASA’s chief historian, has long maintained that a biologically based (versus a machine-based) technological civilization is a brief phenomenon limited to a few thousand years and “exists in the universe in the proportion of one thousand to one billion, so that only one in a million civilizations are biological.”
Cuntz, however, says there’s no way to be certain about those odds.
“We really have to do more work,” he says with a smile, “but we may not be alone.”
— David Van Meter