One of the major surprises of MESSENGER's orbital mission is the discovery of an unexpected class of shallow, irregular depressions (arrows). Some of the depressions have bright interiors and halos (white arrows). The science team is referring to these features as "hollows" in order to distinguish them from other types of non-impact depressions found on Mercury (volcanic vents, collapse pits). This image, a figure from a paper published in the Sept. 30, 2011 issue of the journal Science, shows hollows on the peak-ring mountains of an unnamed 170-km-diameter impact basin (inset). The origin of the hollows is not certain, but may involve loss of volatile material.

This is Figure 1A of Blewett et al. (2011) Science vol. 333, #6050.

This image was acquired as a high-resolution targeted observation. Targeted observations are images of a small area on Mercury's surface at resolutions much higher than the 250-meter/pixel (820 feet/pixel) morphology base map or the 1-kilometer/pixel (0.6 miles/pixel) color base map. It is not possible to cover all of Mercury's surface at this high resolution during MESSENGER's one-year mission, but several areas of high scientific interest are generally imaged in this mode each week.

Date acquired: May 14, 2011
Image Mission Elapsed Time (MET): 213851669
Image ID: 251497
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Center Latitude: 34.42°
Center Longitude: 282.0° E
Resolution: 15 meters/pixel
Scale: 5 kilometers is about 3 miles.
Incidence Angle: 66.3°
Emission Angle: 32.7°
Phase Angle: 33.6°

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.