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Planets have to be about the size of Earth to be conducive for life

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Event Horizon
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« on: September 12, 2009, 11:20:15 pm »

Planets have to be about the size of Earth to be conducive for life
ANI 8 September 2009, 12:42pm IST

LONDON: In a new research, it has been determined that rocky worlds have to be about the size of Earth to be conducive for life.

According to a report in the New Scientist, the discovery of extra solar 'super-Earths' - rocky planets about five to ten times the mass of Earth - has raised hopes that some may harbor life.

Life is comfortable on Earth in part because of its relatively stable climate and its magnetic field, which deflects cosmic radiation capable of damaging organic molecules as well as producing amazing auroras.

The long term stability of Earth's climate depends on the way the planet's crust is broken up into plates, which continually slide over and under one another in a process called plate tectonics. Carbon scrubbed from the atmosphere by natural chemical reactions gets buried and recycled within the Earth because of plate tectonics, part of a cycle that stabilizes atmospheric carbon dioxide concentrations.

Now, it seems rocky worlds have to be about the size of Earth to have both plate tectonics and magnetic fields, according to Lade Stamenkovic of the German Aerospace Center in Berlin.

Heat from Earth's core creates the convection currents needed for plate tectonics. Such currents generate the force to tear the crust, produce multiple plates and move those plates around.

Stamenkovic's team found that the pressure and viscosity inside a 'super-Earth' would be so high that a stagnant, insulating layer would form outside the core, weakening the convective currents needed to drive plate tectonics thus making the process unlikely.

The researchers also found that the slow transfer of heat out of the core in 'super-Earths' would prevent a sufficiently rapid circulation of their molten cores, robbing them of a magnetic field.

Planets about 0.5 to 2.5 times the mass of Earth are most likely to support plate tectonics. The limits are fuzzier for magnetic field generation, but also favour Earth-sized planets.

"Earth is special," said Stamenkovic.

But astrobiologist David Grinspoon of the Denver Museum of Nature and Science in Colorado points out that Venus seems to have recycled its crust in volcanic outbursts despite a lack of plate tectonics.

While this has not stabilized Venus's climate, the possibility that other forms of crustal recycling on super-Earths might do so should not be ruled out.
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