This image shows a detailed view of the irregular depression seen in the enhanced color image released earlier this week during the NASA Science Update telecon. This region of high reflectance was just barely seen on the limb during MESSENGER's second flyby, but without enough detail to characterize it as anything other than a bright spot. A more favorable viewing angle reveals this bright spot to be an irregular rimless depression approximately 30 kilometers across surrounded by highly reflective material. Its features are distinctly different from those of impact craters and, though its origin remains ambiguous, it is suspected to be volcanic, possibly the site of an explosive volcanic vent. The high-reflectance halo surrounding this enigmatic feature is distinct in color (see the enhanced color image) and may represent a pyroclastic deposit greater than 150 kilometers in diameter.

Date Acquired: September 29, 2009
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Scale: The irregular rimless depression in the center of the image is approximately 30 kilometers (19 miles) across

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.