[meteorite-list] MESSENGER: New Images Shed Light on Mercury's Geological History, Surface Textures

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 17 Jan 2008 14:12:45 -0800 (PST)
Message-ID: <200801172212.OAA11759_at_zagami.jpl.nasa.gov>

http://messenger.jhuapl.edu/news_room/status_report_01_17_08.html

MESSENGER Mission News
January 17, 2008

New Images Shed Light on Mercury's Geological History, Surface Textures
MESSENGER Reveals Mercury's Geological History

Shortly following MESSENGER's closest approach to Mercury on January 14,
2008, the spacecraft's Narrow Angle Camera (NAC) on the Mercury Dual
Imaging System (MDIS) instrument acquired this image
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=121>
as part of a mosaic that covers much of the sunlit portion of the
hemisphere not viewed by Mariner 10. Images such as this one can be read
in terms of a sequence of geological events and provide insight into the
relative timing of processes that have acted on Mercury's surface in the
past.

The double-ringed crater pictured in the upper right of this image
appears to be filled with smooth plains material, perhaps volcanic in
nature. This crater was subsequently disrupted by the formation of a
prominent scarp (cliff), the surface expression of a major crustal fault
system, that runs alongside part of its southern rim and may have led to
the uplift seen across a portion of the crater's floor. A smaller crater
in the upper left of the image has also been cut by the scarp, showing
that the fault beneath the scarp was active after both of these craters
had formed.

The MESSENGER team is working to combine inferences about the timing of
events gained from this image with similar information from the hundreds
of other images acquired by MESSENGER to extend and refine the
geological history of Mercury previously defined on the basis only of
Mariner 10 images.

This MESSENGER image was taken from a distance of about 18,000
kilometers (11,000 miles) from the surface of Mercury, at 20:03 UTC,
about 58 minutes after the closest approach point of the flyby. The
region shown is about 500 kilometers (300 miles) across, and craters as
small as 1 kilometer (0.6 mile) can be seen in this image.

------------------------------------------------------------------------

MESSENGER Views Mercury's Horizon

As the MESSENGER spacecraft drew closer to Mercury for its historic
first flyby, the spacecraft's Narrow Angle Camera (NAC) on the Mercury
Dual Imaging System (MDIS) acquired an image mosaic of the sunlit
portion of the planet. This image
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=122>
is one of those mosaic frames and was acquired on January 14, 2008,
18:10 UTC, when the spacecraft was about 18,000 kilometers (11,000
miles) from the surface of Mercury, about 55 minutes before MESSENGER's
closest approach to the planet.

The image shows a variety of surface textures, including smooth plains
at the center of the image, many impact craters (some with central
peaks), and rough material that appears to have been ejected from the
large crater to the lower right. This large 200-kilometer-wide (about
120 miles) crater was seen in less detail by Mariner 10 more than three
decades ago and was named Sholem Aleichem for the Yiddish writer. In
this MESSENGER image, it can be seen that the plains deposits filling
the crater's interior have been deformed by linear ridges. The shadowed
area on the right of the image is the day-night boundary, known as the
terminator. Altogether, MESSENGER acquired over 1200 images of Mercury,
which the science team members are now examining in detail to learn
about the history and evolution of the innermost planet.

------------------------------------------------------------------------

Additional information and features from MESSENGER's first flyby of
Mercury will be available online at
http://messenger.jhuapl.edu/mer_flyby1.html. Following the flyby, be
sure to check for the latest released images and science results!

------------------------------------------------------------------------

MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and
Ranging) is a NASA-sponsored scientific investigation of the planet
Mercury and the first space mission designed to orbit the planet closest
to the Sun. The MESSENGER spacecraft launched on August 3, 2004, and
after flybys of Earth, Venus, and Mercury will start a yearlong study of
its target planet in March 2011. Dr. Sean C. Solomon, of the Carnegie
Institution of Washington, leads the mission as principal investigator.
The Johns Hopkins University Applied Physics Laboratory built and
operates the MESSENGER spacecraft and manages this Discovery -class
mission for NASA.
Received on Thu 17 Jan 2008 05:12:45 PM PST