Other Solar Systems More Habitable Than Ours
December 4, 2012

Variations In Radioactive Elements May Help Search For Alien Life

Lee Rannals for redOrbit.com - Your Universe Online

A new study has found that many planets in other solar systems may be more habitable than our very own.

Astronomers and geologists at Ohio State University teamed up to search for alien life in a whole new way; by studying eight "solar twins" of our sun in order to measure the amounts of radioactive elements they contain.

Those stars came from a dataset recorded by the High Accuracy Radial Velocity Planet Searcher (HARPS) spectrometer at the European Southern Observatory in Chile.

The researchers looked through the solar twins for elements like thorium and uranium, which are both essential to Earth's plate tectonics. Plate tectonics help to maintain water on the surface of Earth, so another planet having this feature is an indicator of planet's hospitality to life.

Of the eight solar twins observed, seven seem to contain much more thorium than our sun, suggesting that planets orbiting those stars contain more thorium as well.

Ohio State doctoral student Cayman Unterborn says one star in the survey contains 2.5 times more thorium than our sun. He found that terrestrial planets that formed around that star probably generated 25 percent more internal heat than Earth, allowing plate tectonics to persist longer through a planet's history.

“If it turns out that these planets are warmer than we previously thought, then we can effectively increase the size of the habitable zone around these stars by pushing the habitable zone farther from the host star, and consider more of those planets hospitable to microbial life,” said Unterborn, who presented the results at the American Geophysical Union meeting in San Francisco this week.

He said that at this point, all we can say is that there is some natural variation in the amount of radioactive elements inside stars like ours.

"With only nine samples including the sun, we can´t say much about the full extent of that variation throughout the galaxy," Unterborn said. "But from what we know about planet formation, we do know that the planets around those stars probably exhibit the same variation, which has implications for the possibility of life.”

Wendy Panero, associate professor in the School of Earth Sciences at Ohio State, said that radioactive elements like thorium, uranium, and potassium are present within Earth's mantle.

“The core is hot because it started out hot,” Panero said. “But the core isn´t our only heat source. A comparable contributor is the slow radioactive decay of elements that were here when the Earth formed. Without radioactivity, there wouldn´t be enough heat to drive the plate tectonics that maintains surface oceans on Earth.”

The researchers say the relationship between plate tectonics and surface water is complicated, with Panero calling it "one of the great mysteries in the geosciences."

Researchers are beginning to suspect that the same forces of heat convection in the mantle that move Earth's crust regulate the amount of water in oceans.

“It seems that if a planet is to retain an ocean over geologic timescales, it needs some kind of crust ℠recycling system,´ and for us that´s mantle convection,” Unterborn said.

Microbial life on Earth benefits from subsurface heat, and scores of microbes known as archaea do not rely on the sun for energy. Instead, they live directly off of heat arising from inside the Earth.

Most of the heat from radioactive decay comes from uranium on Earth. Unterborn said that planets rich in thorium would "run" hotter and remain hot longer, giving them more time to develop life.