September 26, 2012
Super-Earths May Not Be As Earth-Like As Name Suggests
Lee Rannals for redOrbit.com — Your Universe Online
A new study presented at the European Planetary Science Congress on Wednesday shows just how rare our Earth really is.
"We are discovering planets orbiting distant stars that are similar to Earth in composition but more massive than Earth. The major question is: are they just scaled-up versions of Earth, or are they fundamentally different?," Dr. Vlada Stamenkovic, a researcher at the Massachusetts Institute of Technology, said in a press release.
"Some of these features are crucial for determining if a planet might be capable of supporting surface life," Stamenkovic continued.
The Earth hosts plate tectonics and volcanic activity to help regulate the climate and release and recycle nutrients for life.
Our planet's magnetic field is driven by a liquid metallic core, and even protects the atmosphere from being stripped away by solar and cosmic particles.
The researchers have found that the viscosity and the melting temperature of mantle rock are strongly affected by pressure.
The team said that in super-Earths, internal pressures are tens of times greater than those in the terrestrial interior, and can lead to large viscosities and melting temperatures. This can negatively impact the habitability of a planet.
The calculations made by the researchers suggest that rock super-Earths may not be separated into a metallic core and rocky mantle like Earth.
"Current understanding is that the terrestrial planets in our solar system formed rapidly–in about the first 50 million years," Stamenkovic said in the release. "The time scale of core formation depends strongly on viscosity. The high melting temperatures and the large viscosities that we've calculated for super-Earths suggest either a slow core formation or no core formation at all. This raises doubts about whether super-Earths could generate magnetic fields."
The research shows that convection would be sluggish, or that stagnant layers which form deep in the mantle of those super-Earths are differentiated.
The team found the propensity of plate tectonics to decline with planetary mass as well, and they also found that water in the lithosphere can easily buffer these effects, making plate tectonics on super-Earths depend on a set of unknown planetary characteristics.
They said the duration of volcanic outgassing and the production of molten rock generally decrease with increasing planetary mass. This could limit the timescales for ongoing volcanic activity on super-Earths.
"Our work highlights the importance of understanding the thermal evolution of planets–moreover, it shows that super-Earths are more diverse than expected," Stamenkovic said. "We will only be able to fully answer questions by gathering more data from high-pressure experiments and from spectroscopic observations of super-Earth atmospheres orbiting close-by bright stars."
He said the theory shows the possibilities are far larger than previously thought, but are a lot more uncertain as well.