Some impact craters on Mercury have non-circular, irregularly shaped depressions or pits on their floors. Such craters have been termed pit-floor craters, and MESSENGER team members have suggested that such pits formed by the collapse of subsurface magma chambers. If this suggestion is correct, the pits are evidence of volcanic processes at work on the Solar System's innermost planet. With high-resolution images from MESSENGER's third Mercury flyby, more pit-floor craters are being identified on Mercury's surface. This NAC image shows a good view of a pit-floor crater imaged last week prior to closest approach. The large crater near the center of the image contains an elongated bean-shaped depression on its floor and is a pit-floor crater. The slightly smaller crater to the south also contains a pair of depressions on its floor, though from this image alone it cannot be determined if the depressions are pits or overlapping impact craters. Other examples of pit-floor craters discovered in MESSENGER images include Beckett, Gibran, and another newly imaged crater from Mercury flyby 3.

Date Acquired: September 29, 2009
Image Mission Elapsed Time (MET): 162744290
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Resolution: 390 meters/pixel (0.24 miles/pixel)
Scale: This image is about 400 kilometers (250 miles) from top to bottom
Spacecraft Altitude: 15,200 kilometers (9,400 miles)

These images are from MESSENGER, a NASA Discovery mission to conduct the first orbital study of the innermost planet, Mercury. For information regarding the use of images, see the MESSENGER image use policy.