Using images from NASA’s MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) spacecraft, planetary researchers have discovered a broad valley in the southern hemisphere of the planet Mercury.
Using colorized topography, Mercury’s ‘great valley’ (dark blue) and Rembrandt impact basin (purple, upper right) are revealed in this high-resolution digital elevation model merged with an image mosaic obtained by NASA’s MESSENGER spacecraft. Image credit: NASA / Johns Hopkins University Applied Physics Laboratory / Carnegie Institution of Washington / DLR / Smithsonian Institution.
The team, led by Dr. Thomas Watters, a researcher at the Smithsonian National Air and Space Museum, used MESSENGER images to create a high-resolution map that revealed the broad valley extending into the Rembrandt basin, one of the youngest impact basins on Mercury.
Mercury’s great valley is more than 620 miles (1,000 km) long, 250 miles (400 km) wide and 2 miles (3 km) deep. It is smaller than Mars’ Valles Marineris, but larger than North America’s Grand Canyon and wider and deeper than the Great Rift Valley in East Africa.
“Unlike Earth’s Great Rift Valley, 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,” Dr. Watters said.
The valley is bound by two large fault scarps — cliff-like landforms that resemble stair steps.
The scarps formed as Mercury’s interior cooled; the planet’s shrinking was accommodated by the crustal rocks being pushed together, thrusting them upward along fault lines.
However, the valley is not only the product of two large, parallel, fault scarps — the elevation of the valley floor is below that of the surrounding terrain, suggesting that another process may be at work.
The most likely explanation for the valley is long-wavelength buckling of the planet’s outermost shell in response to global contraction or shrinking.
“The association of the valley and the contractional tectonic landforms (lobate scarps and high-relief ridges) suggests that the valley and bounding structures may have been localized by a long-wavelength, lithospheric-scale mechanism,” the researchers said.
“One such mechanism is buckling of the lithosphere, a mechanism proposed to accommodate a fraction of the horizontal contraction on Mercury.”
According to the team, cooling of Mercury’s interior caused the planet’s single outer crust plate to contract and bend. Crustal rocks were thrust upward while the emerging valley floor sagged downward. The sagging valley floor lowered part of the rim of the Rembrandt basin as well.
“There are similar examples of this on Earth involving both oceanic and continental plates, but this may be the first evidence of this geological process on Mercury,” Dr. Watters said.
The findings were published this week in the journal Geophysical Research Letters.
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Thomas R. Watters et al. Fault-bound valley associated with the Rembrandt basin on Mercury. Geophysical Research Letters, published online November 16, 2016; doi: 10.1002/2016GL070205
This article is based on a press-release issued by NASA.
