Large valley found on Mercury

A large valley has been discovered on Mercury that could be evidence of buckling of the planet's crust due to its cooling.

A model of Mercury’s surface created using stereo images obtained by NASA’s MESSENGER spacecraft reveals the planet’s great valley.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/DLR/Smithsonian Institution.

Images captured by NASA’s MESSENGER spacecraft have revealed a large valley on Mercury that could be the first evidence of contraction of the planet’s outer shell due to cooling.

The valley is about 400km wide and about 3km deep. It is over 1,000km long and extends into the Rembrandt basin, which is one of the largest and youngest impact basins on Mercury.

The contraction has occurred in the planet’s lithosphere, which consists of its crust and upper mantle. While Earth’s lithosphere is made up of many tectonic plates, Mercury’s is just one plate. This contraction is thought to be caused by cooling of the planet’s interior, which makes Mercury’s plate contract and bend.

“There are examples of lithospheric buckling on Earth involving both oceanic and continental plates, but this may be the first evidence of lithospheric buckling on Mercury,” says Thomas R. Watters, lead author of the new study.

The valley is bordered by two large ‘steps’ known as fault scarps. These scarps are created when one side of a fault has moved vertically with respect to the other. In Mercury’s case, contraction has caused the fault scarps bordering the valley to increase in size so that they have formed cliff-like features.

“Unlike Earth’s Great Rift Valley in East Africa, Mercury’s Great Valley is not caused by the pulling apart of lithospheric plates due to plate tectonics; it is the result of the global contraction of a shrinking one-plate planet,” says Watters. “Even though you might expect lithospheric buckling on a one-plate planet that is contracting, it is still a surprise when you find that it’s formed a great valley that includes the largest fault scarp and one of the largest impact basins on Mercury.”

Carousel image: A MESSENGER image of Mercury as the spacecraft neared the planet on 14 January 2008.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
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