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Meet Mercury, the solar system's incredibly shrinking planet


In this handout from NASA, Mercury is seen from the Messenger spacecraft on Jan. 14, 2008.


NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The smallest planet in our solar system is getting even smaller.

Mercury, the first scorched rock from the Sun, has contracted into itself even more than previously thought over the past 4 billion years, according to new research using images from NASA's MESSENGER spacecraft.

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The proof is in its stretch marks.

Looking at tectonic features like wrinkle edges and rounded cliffs (similar to wrinkles on our skin), researcher determined Mercury has shrunk up to 8.6 miles in diameter over the course of several millennia.

The shrinkage is a result of the huge temperature difference between Mercury's core and its surface.

As heat from the interior tries to escape to the surface, the planet contracts.

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"It solves a mystery that's been lingering for a while," planetary scientist William McKinnon of Washington University in Saint Louis told Discovery. "Mariner 10 (in the 1970s) first saw these giant cliffs."

So scientists knew Mercury was shrinking as early as the 1970s. They just didn't know how much -- or how fast.

Heat rises to the surface in pretty much every planet. But don't worry, Earth isn't shrinking.

Our home planet has constantly shifting tectonic plates, while Mercury is a single-plate planet.

Learn more about this strange, hot little world in the video below: