SOURCE: New Scientist
14 October 2007
"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 have plate tectonics.
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."
This article: http://www.newscientist.com/article/mg19626255.500