New calculations may further limit habitable zones around distant suns

June 11th, 2009 - 3:32 pm ICT by ANI  

Washington, June 11 (ANI): New calculations by scientists indicate that tidal forces exerted on planets by the parent star’s gravity could limit what is regarded as a star’s habitable zone and change the criteria for planets where life could potentially take root.

Scientists believe liquid water is essential for life. But, a planet also must have plate tectonics 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,” said Rory Barnes, a University of Washington postdoctoral researcher in astronomy.

“However, 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 added.

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.

Barnes uses new calculations from computer modeling to define a “tidal habitable zone.”

“Our model predicts that tides may contribute only one-quarter of the heating required to make the planet habitable, so a lot of heat from decay of radioactive isotopes may be required to make up the difference,” Jackson said.

“The bottom line is that tidal forcing is an important factor that we are going to have to consider when looking for habitable planets,” said Barnes.

“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. The best places to look for habitability are where this new definition and the old definition overlap,” he added.

The new calculations have implications for planets previously considered too small for habitability.

An example is Mars, which used to experience tectonics but that activity ceased as heat from the planet’s decaying inner core dissipated.

But as planets get closer to their suns, the gravitational pull gets stronger, tidal forces increase and more energy is released.

If Mars were to move closer to the sun, the sun’s tidal tugs could possibly restart the tectonics, releasing gases from the core to provide more atmosphere.

If Mars harbors liquid water, at that point it could be habitable for life, as we know it. (ANI)

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