'Super Earths' Will Have Plate Tectonics, Scientists Predict

November 21, 2007 feature

The discoveries of large Earth-like planets outside our Solar System, so-called “super-Earths,” has prompted much speculation about just how Earth-like they may be. Recently, scientists from Harvard University suggested that these planets will, like Earth, have plate tectonics.

Plate tectonics, the movement of the giant plates that make up Earth's solid outer shell, are responsible for earthquakes, volcanoes, and other major geological events. In essence, they have dominated Earth's geological history. Earth is the only known planet that has plate tectonics, and this activity has been proposed as one necessary condition for the evolution of life.

However, in a paper published in The Astrophysical Journal, Harvard planetary scientist Diana Valencia and her colleagues predict that super-Earths – which are between one and ten times as massive as Earth – will fulfill one of the requirements for sustaining life by having plate tectonics.

“Some of these super-Earths may be in the 'habitable zone' of their solar systems, meaning they are at the right distance from their mother star to have liquid water, and thus life,” Valencia, the paper's corresponding author, told PhysOrg.com. “Ultimately, though, only these planets' thermal and chemical evolution will determine whether they are habitable. But these thermal and chemical properties are closely tied to plate tectonics.”

Using detailed models they developed of the interior of massive terrestrial planets, Valencia and her group determined how the mass of a super-Earth is related to the thickness of its plates and the magnitude of the stresses the plates experience. These stresses, part of the slow, slow convection of Earth's mantle, are the driving force behind the deformation and subduction (when one plate sinks below another) of the plates. For planets more massive than Earth, this driving force is larger than Earth's.

The group found that as planetary mass increases, there is an increase in the shear stress and a decrease in the plate thickness. Both of these factors weaken the plates and contribute to plate subduction, which is a key component of plate tectonics. Therefore, the scientists say, the conditions required for plate deformation and subduction are easily met by super-Earths. Their results show that this is particularly true for the larger super-Earths.

“Our work strongly suggests that super-Earths, even if they have no water, will exhibit plate tectonic behavior,” Valencia said.

In the future, it may be possible to verify these results using NASA's Terrestrial Planet Finder devices or the European Space Agency's Darwin project, which will consist of three telescopes to search out Earth-like planets.

Citation: Diana Valencia, Richard J. O'Connell, and Dimitar D. Sasselov “Inevitability of Plate Tectonics on Super-Earths” The Astrophysical Journal, volume 670, part 2 (2007)

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

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3.8 / 5 (5) Nov 21, 2007
I wonder if their simulations show anything about our own Earth having an unusually thin shell due to the manner in which the moon was formed?
2.3 / 5 (4) Nov 22, 2007
Earth crust is thickest under less dense continents, thin under higher density oceanic plates. This is called isostasy, Pratt hypothesis. Larger earths crusts would depend on compositions.
3 / 5 (6) Nov 22, 2007
The article states "%u201COur work strongly suggests that super-Earths, even if they have no water, will exhibit plate tectonic behavior,%u201D Valencia said."

Without recallling that I ever read it. I had the impression that water was essential in many, if not most, of the plate tectonics functions.

Was/am I completely out of my league?
3.2 / 5 (6) Nov 22, 2007
No, you're not completely out of your league.

On Earth, water is essential to plate tectonics, and it should be the same for [i]all[/i] earth mass planets, however, what the article is saying, in a nut shell, is that as a rocky terrestrial planet increases, the thickness of it's crust decreases, and the convective forces in the mantle increase. Basicaly, as the earth like planets get bigger, the driving forces of plate tectonics get stronger, and the ability of the planets crust to resist them get weaker. That help at all?
2.5 / 5 (6) Nov 23, 2007
Water does not drive plate tectonics. Mantle convection does.
3.3 / 5 (4) Nov 23, 2007
Nobody is saying that water drives mantle convection, however, without the presenc of water in the crust, and on the surface of the earth, the Earth would not have plate tectonics.

Maybe you need to read my post again.
1 / 5 (4) Nov 25, 2007
1.7 / 5 (3) Nov 25, 2007
What's taking so long for the Terrestrial Planet Finder or any other similar mission? Why it always takes so long? In my view space missions of critical importance (manned or unmanned) are snail paced. No wonder science is itself progressing slowly.
2.3 / 5 (3) Nov 28, 2007
usman_exc, there's a lot of precision and details that go into this type of advanced research. Even if the experiment last less than a second, the prep and cleanup is still going to take quite some time. Just think back to how annoying those labs in High School/College were... Not because of the science, but the scientific method.

Doing things right the first time is definitely a much better option than FUD.
2.3 / 5 (3) May 19, 2008
As I understand it, Earth "should" have had a thicker atmosphere and a thicker crust, and would have had both, but for the impact that formed the Moon. Without this event, Earth would have turned out rather like Venus. It seems that most Earth-sized planets are probably more "Venusian" than "Terrestrial", with dense atmospheres, thicker crusts and no plate tectonics.

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