Long Scarps on Mercury Tell of the Planet's Unique History

Extending from the left edge of this image diagonally toward the lower right corner is a long scarp (cliff) face. This scarp runs through a large ancient crater in the center of the frame and was seen for the first time during MESSENGER's second Mercury flyby. Planetary geologists use the Latin term "rupes" for scarps on Mercury. Scarps such as this one have been identified all over the planet. The presence of many long and high scarps suggests a history for Mercury that is unlike that of any of the other planets in the Solar System. These giant scarps are believed to have formed when Mercury's interior cooled and the entire planet contracted slightly as a result, causing the surface rocks to fracture and some blocks of crust to thrust over others along great faults. Determining the geometry of such scarps on Mercury and information on the times that deformation occurred can thus be used to understand the thermal history of the planet. Next year, when the MESSENGER spacecraft is in orbit around Mercury, MDIS will acquire for the first time global imaging coverage of Mercury's surface with lighting conditions optimal for identifying such scarps.

Source: Courtesy NASA/JPL-Caltech.

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