[meteorite-list] MESSENGER: Counting Mercury's Craters

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 25 Jan 2008 09:00:33 -0800 (PST)
Message-ID: <200801251700.JAA01101_at_zagami.jpl.nasa.gov>

http://messenger.jhuapl.edu/news_room/status_report_01_24_08.html

MESSENGER Mission News
January 24, 2008

Counting Mercury's Craters

On January 14, 2008, MESSENGER flew by Mercury and snapped images of a
large portion of the surface that had not been previously seen by
spacecraft. Ever since the first images were received back on Earth one
day later, January 15, MESSENGER team members have been closely
examining and studying this "new" terrain with great interest and
excitement.

One of many investigations underway includes identifying and measuring
the impact craters on these previously unseen regions. The density of
craters on the surface of a planet can be used to indicate the relative
age of different places on the surface; the more craters the surface has
accumulated, the older the surface. By counting craters on different
areas of Mercury's surface, a relative geologic history of the planet
can be constructed, indicating which surfaces formed first and which
formed later.

However, this process is also time consuming; Mercury has a lot of
craters! This image
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=136>
shows just a portion (276 kilometers, or 172 miles, wide) of one frame
taken with the Narrow Angle Camera (NAC) of the Mercury Dual Imaging
System (MDIS). In this image alone, 763 craters have been identified and
measured (shown in green) along with 189 hills (shown in yellow).
Altogether, 491 frames were taken by the NAC to create high-resolution
mosaics of Mercury's surface.

Of course, simply counting the craters is not enough. Each crater has to
be measured and classified to fully interpret the differences in crater
density. Many small craters form as "secondaries," as clumps of material
ejected from a "primary" crater re-impact the surface in the regions
surrounding the primary. In order to learn about the history of asteroid
and comet impacts on Mercury, scientists have to distinguish between the
primary and secondary craters. Once many more craters are measured,
MESSENGER researchers will have new insights into the geological history
of Mercury.

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

Additional information and features from this first flyby will be
available online at http://messenger.jhuapl.edu/mer_flyby1.html, so
check back frequently. 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 Fri 25 Jan 2008 12:00:33 PM PST