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Sunday, October 14, 2007
Super-Earths plate tectonics
Super-Earths will have plate tectonics
Super-Earths" - rocky planets up to 10 times the mass of Earth that orbit other stars - probably have similar structures to our world, with a solid inner core surrounded by a liquid mantle and then a crust. They may even have plate tectonics, which some argue is necessary for life to evolve.
Dimitar Sasselov of the Harvard-Smithsonian Center for Astrophysics and colleagues came to this conclusion after modelling geological processes on planets of various sizes. They found that as planetary mass increases, more heat is trapped and convection increases. As a result the shear stress within the crust increases too and plate thickness decreases. That means the plates are weaker and plate tectonics becomes "inevitable" (www.arxiv.org/abs/0710.0699v1). Our own planet seems to lie at the threshold. If it were any less massive, it would probably not be geologically active.
Plate tectonics may boost biodiversity by recycling chemicals and minerals through the crust. "When it comes to habitability, super-Earths are our best destination," says Sasselov.
"The idea is right," says Jack Lissauer of NASA's Ames Research Center in Moffett Field, California. "Plate tectonics is more likely on more massive planets."
Abstract
The recent discovery of super-Earths (masses less or equal to 10 earth-masses) has initiated a discussion about conditions for habitable worlds. Among these is the mode of convection, which influences a planet's thermal evolution and surface conditions. On Earth, plate tectonics has been proposed as a necessary condition for life. Here we show, that super-Earths will also have plate tectonics. We demonstrate that as planetary mass increases, the shear stress available to overcome resistance to plate motion increases while the plate thickness decreases, thereby enhancing plate weakness. These effects contribute favorably to the subduction of the lithosphere, an essential component of plate tectonics. Moreover, uncertainties in achieving plate tectonics in the one earth-mass regime disappear as mass increases: super-Earths, even if dry, will exhibit plate tectonic behaviour.
Google stock soars to record high
Shares of Google Corp. (Nasdaq: GOOG) soared to a record high Tuesday in pre-market trading on an optimistic outlook toward Google's third-quarter results with many analysts raising their price estimates to $700 a share.
Shares of Google are up 32 percent for the year and this morning's high of $615 is the seventh record in the past two weeks putting co-founders Larry Paige and Sergey Brin's personal stake in Google well over $17 billion each.
Since going public three years ago at $85 per share, Google's value has climbed to $187 billion; more than Coca Cola, IBM or retail giant, Wal-Mart Stores - a more than seven-fold increase.
Google is set to release its third-quarter results on October 18th.
Analysts on average are estimating that Google will report $3.75 per share in earnings, which is a 40 percent increase.
Buoyed by recent gains in search engine market share over rivals Yahoo! Corp (Nasdaq: YHOO) and Microsoft Corp.'s MSN (Nasdaq: MSFT), tech investors are showing their confidence in Google's stock at a time when other tech companies are reporting strong results.
Shares of Google were trading up $5.88, or nearly 1%, at $615.25 as of 8am EST Tuesday, a new 52-week hi.
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