Hollows on the Northern Wall of an Impact Crater

Do hollows form preferentially on crater walls that receive more direct sunlight? In the northern hemisphere, the northern walls of craters are frequently sunlit, while the southern walls receive more grazing sunlight and are more often in shadow. (In the southern hemisphere it is the opposite.) The greater solar heating experienced by the northern wall may be an important factor in the formation of hollows. Images like the one here can help answer this question and are an area of focus for MESSENGER's current low-altitude imaging campaign. See these two other examples of hollows in craters walls.

This image was acquired as part of the MDIS low-altitude imaging campaign. During MESSENGER's second extended mission, the spacecraft makes a progressively closer approach to Mercury's surface than at any previous point in the mission, enabling the acquisition of high-spatial-resolution data. For spacecraft altitudes below 350 kilometers, NAC images are acquired with pixel scales ranging from 20 meters to as little as 2 meters.

Date acquired: February 25, 2014
Image Mission Elapsed Time (MET): 35646241
Image ID: 5828285
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 42.92°
Center Longitude: 330.9° E
Resolution: 17 meters/pixel
Scale: This crater has a diameter of 12.5 kilometers (7.8 miles)
Incidence Angle: 43.5°
Emission Angle: 46.1°
Phase Angle: 30.1°

Photo credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington