Mercury Is Shrinking

Almost 9 miles narrower

Mercury has shrunk almost nine miles in diameter.     Photo: Courtesy of NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The solar system’s smallest planet is getting even smaller.

Mercury has shrunk almost nine miles in diameter over the past four billion years, according to a report published Sunday. The reason? The planet is cooling, making its single tectonic plate contract and warp the surface into rocky ridges.

"It is Mercury's version of a mountain belt," Paul Byrne, a planetary geologist and lead author of the study, told National Geographic. "It would be a very dramatic landscape." 

All of the planets in the solar system are getting colder, and Mercury is no exception, despite its proximity to the sun. But the process has taken a harder toll on the small planet, forming cliffs as tall as Mount St. Helens and ridges longer than twice the length of Florida.

The findings come from the Messenger spacecraft, which has circled Mercury since 2011. Now that the ship has successfully mapped the planet’s entire surface, earthbound scientists have a detailed map of the alien landscape.

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