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TOPIC: Terrestrial Exoplanets


L

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RE: Terrestrial Exoplanets
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How common are alien Earths - small, rocky planets orbiting at the right distance to be not so hot that water boils and not so cold that it stays frozen? Till now clues have been hard to come by, because surveys have not been sensitive enough to find many such planets.
That should soon change thanks to the Kepler space telescope, which NASA is expecting to launch on 5 March. Its unique positioning in the solar system and unprecedented sensitivity mean that for the first time we will be able to see Earth-size planets in the "habitable zone" of their stars - the region where the temperature on the planet should be right for liquid water to exist at its surface.

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L

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Earth-like planets may in fact be common in the galaxy, increasing the likelihood of extraterrestrial life.
By observing the remains of smashed up asteroids around dead stars, astronomers were able to deduce their chemical composition. They found that the dust of many chewed-up asteroids resembles the materials inside Earth and the other small, rocky inner planets of our solar system.

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Title: Coreless Terrestrial Exoplanets
Authors: L. Elkins-Tanton, S. Seager (MIT)

Differentiation in terrestrial planets is expected to include the formation of a metallic iron core. We predict the existence of terrestrial planets that have differentiated but have no metallic core--planets that are effectively a giant silicate mantle. We discuss two paths to forming a coreless terrestrial planet, whereby the oxidation state during planetary accretion and solidification will determine the size or existence of any metallic core. Under this hypothesis, any metallic iron in the bulk accreting material is oxidised by water, binding the iron in the form of iron oxide into the silicate minerals of the planetary mantle. The existence of such silicate planets has consequences for interpreting the compositions and interior density structures of exoplanets based on their mass and radius measurements.

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