Mercury, the Smallest Planet, Is Getting Even Smaller


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Like a raisin spinning around the sun, Mercury is shrinking and wrinkling. The planet is now up to 8.6 miles (14 kilometers) smaller in diameter than it was nearly four billion years ago, according to a report released on Sunday.

The planet is downsizing because it is cooling. Images snapped by a NASA spacecraft have provided the first complete picture of how the single rocky plate that encapsulates Mercury is contracting, warping the surface into puckered ridges and scallop-edged cliffs known as lobate scarps.

"It is Mercury's version of a mountain belt," Paul Byrne, a planetary geologist at the Carnegie Institution in Washington, D.C., and lead author of the study in Nature Geoscience. "It would be a very dramatic landscape."

All planets are chilling and shedding heat to varying degrees, and Mercury is no exception, despite being the closest planet to the sun. But the process has taken an unusual toll on Mercury's already cratered complexion, forming cliffs that can soar up to two miles (three kilometers) high?about as tall as Mount St. Helens?and long chains of aligned ridges that snake across the face of the planet for up to 1,050 miles (1,700 kilometers), more than twice the length of Florida.

 

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