![Click here for annotated version of PIA11244](https://webarchive.library.unt.edu/eot2008/20090120200046im_/http://photojournal.jpl.nasa.gov/figures/PIA11244_fig1_thumb.jpg)
Click on image for larger annotated version
Earlier today, at 4:40 am EDT, MESSENGER passed a mere 200 kilometers
(124 miles) above Mercury’s surface for its closest approach to the planet
during the mission’s second Mercury flyby. Now, the spacecraft is speeding
away from Mercury, acquiring science observations as it goes. The planned
flyby science observations continue for about 20 hours following closest
approach, and only after the completion of all science observations will
the data be transmitted to Earth. For the moment, the MESSENGER team waits.
However, scientists on the team are already eagerly exploring the optical
navigation images acquired just prior to the flyby. Shown here is a NAC
image from the eighth and final optical navigation image set, taken about
14.5 hours before the flyby’s closest approach; Mercury appears as a
thin sunlit crescent. Though much of Mercury is in darkness in this image,
the visible portion had never been seen by spacecraft before. This portion
of Mercury’s surface was not viewed during any of Mariner 10’s three
flybys or during MESSENGER’s first flyby earlier this year. The newly
imaged terrain shows a wide range of geologic features. Near the northern
limb of the planet, extensive smooth plains, possibly volcanic in origin,
are identified. A nearby crater is the brightest feature visible in the
image, suggesting a relatively young age. This bright crater is consistent
with a bright feature seen in Earth-based telescopic observations. In the
southern region, a large basin is seen with a smooth floor, likely also a
product of volcanism. A large scarp that appears to cut through this basin
may have formed as Mercury cooled and contracted.
Many more features in this image have also captured the MESSENGER team’s
interest. Hints of ridges and scarps are barely discernable near the
terminator, and a crater near the limb suggests the presence of intriguing
dark and light materials. With the comparatively low resolution of this
image, any insight that can be gained into these areas is limited. But
that limitation will not last long. After all, this is just an optical
navigation image. Early this morning, MESSENGER acquired a NAC mosaic of
this same area with a resolution ten times higher! As the first images
from the flyby begin to arrive early Tuesday morning, the MESSENGER team
will see these features in great detail as well as other large expanses of
Mercury not yet viewed by spacecraft.
Date Acquired: October 5, 2008
Image Mission Elapsed Time (MET): 131717310
Instrument: Narrow Angle Camera (NAC) of the Mercury Dual Imaging System (MDIS)
Resolution: 7 kilometers/pixel (4 miles/pixel)
Scale: Mercury’s diameter is 4880 kilometers (3030 miles)
Spacecraft Altitude: 270,000 kilometers (170,000 miles)
Sub-spacecraft Latitude and Longitude: 1.6°N, 129.8°E
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.