The smallest planet is getting smaller - Tucson News Now

Smallest planet getting smaller

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Mercury is made mostly of iron. Mercury is made mostly of iron.
TUCSON, AZ (Tucson News Now) -

Mercury, the closest planet to the sun, is smaller now than it was four billion years ago.  This may be a surprise to most people but not to most astronomers. They have known since the 1970s that the first planet and the smallest planet in the solar system has been shrinking at a very slow pace. 

Mercury is a small planet made mostly of iron. It is roughly 5,000 kilometers across, or 3,100 miles in diameter, and has a small rock crust around it which is falling apart by the rocks buckling and breaking down from movement under the surface. The main reason why Mercury is smaller now than it was before is due to the liquid iron core in the center turning to a solid, allowing it to contract.

It was once believed that Earth was a shrinking planet, but we now know that since Earth is made up of multiple plates, the heat Earth's core produces is allowed to escape easily without disturbing the outer crust.

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