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Earth-Matching Planet Eludes Astronomers

Posted on: Tuesday, 21 February 2006, 15:00 CST

By Dan Vergano USA Today

Astronomers have detected more than 150 planets orbiting nearby stars. But there may be trouble finding that "Goldilocks" planet: just the right size and distance from its star to match Earth.

Discoveries of planets only about five to seven times bigger than Earth show that astronomers are closing in on a planet in the "habitable zone," in which temperatures are neither too cold nor too hot for life, suggest researchers such as Princeton's Bohdan Paczynski.

Last month Paczynski was one of the discoverers of the latest "Super Earth," this one only five times bigger than our planet.

"But it may not be so simple," says University of Minnesota physicist Renata Wentzcovitch and colleagues in the current Science magazine. For planets only a few times heavier than Earth, the chemistry of the planet's core may have a big effect on whether future space tourists will ever want to vacation there. In the study, the team examined the Super Earth orbiting the star Gliese 876, which is 15 light-years away (one light-year equals about 5.9 trillion miles.)

The researchers analyzed the chemistry of perovskite, an electronically inert mineral made of oxygen, silicon and magnesium found in the mantle covering the iron cores of planets.

Earth has a thin layer of perovskite in the mantle. Through computer simulations, the study team found that the extra gravity of a Super Earth (twice as strong on its surface as Earth's) would crush these minerals into new forms, ones that would take on the properties of semiconductors or metals, Wentzcovitch says.

The result there would be enhanced heat flow from the planet's core to the surface, which means more volcanoes and "planetquakes."

The effects on the planet's magnetic field from increased electrical activity in the mantle are more difficult to figure out, she says. But such activity might increase the field, which shields the Earth's surface from solar radiation.

The larger point is that there is more to finding another Earth than detecting a planet the same size and the same distance from its star, she says.

Venus and Earth are similar, she notes, but have significant differences in their interior chemistries.

Venus has a more viscous interior that led to a planet-size earthquake hundreds of millions of years ago, she says, and that probably explains the hellish conditions there, where 800-degree winds are lashed by sulfuric acid rain.

Source: Deseret News (Salt Lake City)

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