An Intriguing Dark Halo Target Name:   Mercury Spacecraft:   MESSENGER Produced by:   NASA/JHUAPL Copyright:  Copyright Free Date Released:  October 9, 2008

• MESSENGER Reveals Mercury as Never Seen Before
• Mercury
• MESSENGER

Date Acquired: October 6, 2008
Image Mission Elapsed Time (MET): 131774051
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Resolution: 540 meters/pixel (0.34 miles/pixel)
Scale: This image is about 550 kilometers across (340 miles)
Spacecraft Altitude: 21,000 kilometers (13,000 miles)

A crater discovered in the newly imaged portion of Mercury's surface during MESSENGER's second Mercury flyby has uncommonly dark material within and surrounding the crater. The material is darker than the neighboring terrain such that this crater with a diameter of 180 kilometers (110 miles) is easily identified even in a distant global image of Mercury; it is located just south of the equator near the limb of the planet in this previously released Wide Angle Camera (WAC) image. The dark halo may be material with a mineralogical composition different from the majority of Mercury's visible surface. Craters with similar dark material on or near their rims were seen on the floor of the Caloris basin during MESSENGER's first flyby. Images acquired though the 11 different narrow-band color filters of the WAC during MESSENGER's second flyby will be crucial to an understanding of the nature of this newly seen, unusual feature.

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