05-April-2006, 06:50 PM
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Vulcan Administrator
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Join Date: Oct 2001
Location: Greenbelt, MD
Posts: 25,997
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Why is Mercury so heavy?
Hardcore Mercury had soft edges smashed away
Quote:
A jolting collision between Mercury and a large planetesimal in the solar system's formative years could have left the planet unusually dense, according to a new simulation. And as much as 16 million billion tonnes of the material kicked up by the impact might have rained down on the proto-Earth.
Jonathan Horner and colleagues at the University of Bern, Switzerland, created the model to see whether a collision between an early Mercury – about 2.25 times its current size – and a planetesimal of half Mercury's current size could have produced the first rock from the Sun that we see today.
Mercury is something of a planetary misfit. It is less than 5000 kilometres in diameter, making it slightly smaller than Saturn's giant moon, Titan. Yet it is more than twice as massive as Titan and is thought to have an iron core that accounts for about two-thirds of its mass.
Scientists have suggested several possible explanations, but more direct measurements of the planet are needed to determine how Mercury came to be so dense.
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