Saturday, July 7, 2012

Super-Earth

As I was researching this topic, I was mildly disappointed that the term "super-earth" didn't describe some rare, mega-planet with exotic properties, but they are still pretty cool. A super-earth is a planet with a mass between 1 and 10 earth masses. Greater than 10 earth masses and the planet is called either a giant planet or a gas giant (depending on how much greater than 10 earth masses, and composition). To give you some perspective, the smallest gas giants in our solar system are Neptune and Uranus, weighing 17.1 and 14.5 earth masses respectively.

A comparison of Earth, super-earth COROT 7b and Neptune. Source

The classification of a super-earth has absolutely nothing to do with the planet's composition. It's name might suggest a planet larger than Earth with Earth-like qualities, however, a super-earth can be anything, gaseous, molten, oceanic, etc,. The reason that super-earths are important currently is that they are the easiest to see. I hope that most of you already know that we are scanning the skies looking for extrasolar planets (exoplanets) but if you don't, then let me be the first to inform you that we are. When our telescopes watch the sky, they are intently focused on the varying brightness of the stars. When the brightness of a star dips it means that something has passed infront of it, that something being one of its orbiting bodies. How much the star's brightness decreases indicates the size of that orbiting body. All of this means that larger bodies like super-earths are easier for us to detect. So far scientists have identified smaller super-earths in the habitable zones of their stars, a promising discovery for the possibility of life outside our solar system.

A super-earth and a gas giant have been found orbiting extremely close to one-another in the Kepler-36 system. Source

Two opposing predictions about the surface geology of these large planets have already been proposed. One theory says that larger planets would have much more tectonic activity than Earth because their greater masses would put their thin outer plates under a lot of stress, much more than on already tectonically active Earth. Plus the increased heat from the cores of these planets would create powerful magma currents beneath the surface. The other theory says that the intense gravity associated with the greater masses of these super-earths would lock the the planets tectonic plates in place, thus negating the possibility of surface disruption. Both theories are quite interesting, but some scientists say that they are premature. We still don't even completely understand plate tectonics on earth and we have very few examples of how it might behave on other planets. Still, these predictions could tell us something about the possibility of life on these super-earths.

The solid surface of a planet is just a thin shell. Source

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