MESSENGER Reveals Mercury’s Geological History
Shortly following MESSENGER’s closest approach to Mercury on January 14, 2008, the spacecraft’s Narrow Angle Camera (NAC) on the Mercury Dual Imaging System (MDIS) instrument acquired this image as part of a mosaic that covers much of the sunlit portion of the hemisphere not viewed by Mariner 10. Images such as this one can be read in terms of a sequence of geological events and provide insight into the relative timing of processes that have acted on Mercury's surface in the past.
The double-ringed crater pictured in the upper right of this image appears to be filled with smooth plains material, perhaps volcanic in nature. This crater was subsequently disrupted by the formation of a prominent scarp (cliff), the surface expression of a major crustal fault system, that runs alongside part of its southern rim and may have led to the uplift seen across a portion of the crater’s floor. A smaller crater in the upper left of the image has also been cut by the scarp, showing that the fault beneath the scarp was active after both of these craters had formed.
This MESSENGER image was taken from a distance of about 18,000 kilometers (11,000 miles) from the surface of Mercury, at 20:03 UTC, about 58 minutes after the closest approach point of the flyby. The region shown is about 500 kilometers (300 miles) across, and craters as small as 1 kilometer (0.6 mile) can be seen in this image.
A truly gigantic new species of the dinomyid rodent Josephoartigasia, christened J. monesi, has been discovered from the Pliocene of Uruguay. The skull indicates an animal roughly three metres in length and weighing about one tonne, making it the largest known rodent.