Magazine article Science News

Exoplanets Require Right Stuff for Life: Wrong Makeup Could Nix Tectonic Activity Needed for Biology

Magazine article Science News

Exoplanets Require Right Stuff for Life: Wrong Makeup Could Nix Tectonic Activity Needed for Biology

Article excerpt

For some exoplanets, just being in the Goldilocks zone isn't enough. Planets need to be made of the right stuff to become a cradle of life.

Planets composed of certain element cocktails can't host a continual recycling of Earth-like tectonic plates, new simulations of exoplanet interiors indicate. Measuring the compositions of stars could help astronomers narrow the list of potentially habitable planets, said Cayman Unterborn, who presented the work December 18.

"This is a new way of thinking--astronomers don't think in geology terms," said Unterborn, an extrasolar planetary scientist at Ohio State University. Exoplanet hunters currently treat an exoplanet as potentially habitable if it orbits the right distance from its sun for water to exist in liquid form.

"When we talk about habitable planets, it may not be wise to just say Goldilocks zone--there may be a Goldilocks composition as well," Unterborn said.

Earth's surface is divided into a jigsaw puzzle of shifting rigid plates. When two plates collide, one can dive under the other down into the mantle. This subduction helps regulate carbon dioxide levels in the atmosphere. Without plate tectonics, C[O.sub.2] from volcanic eruptions would accumulate unchecked and cook the planet, as on Venus.

A descending plate is initially too light to sink all the way into the mantle. As pressures mount during descent, however, the atoms in the plate undergo a reorganization that makes the plate denser. This phase change, at roughly 40 kilometers belowground, allows the plate to sink deeper into the mantle. …

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