On January 14, 2008, the MESSENGER spacecraft observed about half of the
hemisphere not seen by Mariner 10. These images, mosaicked together by the
MESSENGER team, were taken by the Narrow Angle Camera (NAC), part of the
Mercury Dual Imaging System (MDIS) instrument, about 20 minutes after
MESSENGER's closest approach to Mercury (2:04 pm EST), when the spacecraft
was at a distance of about 5,000 kilometers (about 3,100 miles). The image
shows features as small as 400 meters (0.25 miles) in size and is about
370 kilometers (230 miles) across.
The image shows part of a large, fresh crater with secondary crater chains
located near Mercury's equator on the side of the planet newly imaged by
MESSENGER. Large, flat-floored craters often have terraced rims from
post-impact collapse of their newly formed walls. The hundreds of
secondary impactors that are excavated from the planet's surface by the
incoming object create long, linear crater chains radial to the main
crater. These chains, in addition to the rest of the ejecta blanket,
create the complicated, hilly terrain surrounding the primary crater. By
counting craters on the ejecta blanket that have formed since the impact
event, the age of the crater can be estimated. This count can then be
compared with a similar count for the crater floor to determine whether
any material has partially filled the crater since its formation. With
their large size and production of abundant secondary craters, these
flat-floored craters both illuminate and confound the study of the
geological history of Mercury.
Mission Elapsed Times (MET) of images: 108826040, 108826045
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.
