June 11, 2009

Add Heat, Then Tectonics: Narrowing the Hunt for Life in Space

Written by Anne Minard

In order to support life, an exoplanet should simply hang out where heat from its star is just right for liquid water. Right?

Not necessarily. New research is suggesting that in order to support life, such a planet might also need plate tectonics, and those are triggered in a narrower band of distance from the parent star.

Rory Barnes, a University of Washington astronomer, is lead author of a paper to be published by The Astrophysical Journal Letters that uses new calculations from computer modeling to define a “tidal habitable zone.”

Besides liquid water, scientists think plate tectonics are needed to pull excess carbon from its atmosphere and confine it in rocks, to prevent runaway greenhouse warming. Tectonics, or the movement of the plates that make up a planet’s surface, typically is driven by radioactive decay in the planet’s core, but a star’s gravity can cause tides in the planet, which creates more energy to drive plate tectonics.

“If you have plate tectonics, then you can have long-term climate stability, which we think is a prerequisite for life,” Barnes said.

The tectonic forces cannot be so severe that geologic events quickly repave a planet’s surface and destroy life that might have gotten a foothold, he said. The planet must be at a distance where tugging from the star’s gravitational field generates tectonics without setting off extreme volcanic activity that resurfaces the planet in too short a time for life to prosper.

“Overall, the effect of this work is to reduce the number of habitable environments in the universe, or at least what we have thought of as habitable environments,” Barnes said. “The best places to look for habitability are where this new definition and the old definition overlap.”

Full article here:

http://www.universetoday.com/2009/06/11/add-heat-then-tectonics-narrowing-the-hunt-for-life-in-space/