[meteorite-list] MESSENGER's First Look at Mercury's Previously Unseen Side

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 15 Jan 2008 17:56:14 -0800 (PST)
Message-ID: <200801160156.RAA11411_at_zagami.jpl.nasa.gov>

http://messenger.jhuapl.edu/news_room/status_report_01_15_08_2.html

MESSENGER Mission News
January 15, 2008

MESSENGER's First Look at Mercury's Previously Unseen Side

When Mariner 10 flew past Mercury three times in 1974 and 1975, the same
hemisphere was in sunlight during each encounter. As a consequence,
Mariner 10 was able to image less than half the planet. Planetary
scientists have wondered for more than 30 years about what spacecraft
images might reveal about the hemisphere of Mercury that Mariner 10
never viewed.

On January 14, 2008, the MESSENGER spacecraft observed about half of the
hemisphere missed by Mariner 10. This image
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=117>
was snapped by the Wide Angle Camera, part of the Mercury Dual Imaging
System (MDIS) instrument, about 80 minutes after MESSENGER's closest
approach to Mercury (2:04 p.m. EST), when the spacecraft was at a
distance of about 27,000 kilometers (about 17,000 miles). The image
shows features as small as 10 kilometers (6 miles) in size. This image
was taken through a filter sensitive to light near the red end of the
visible spectrum (750 nm), one of a sequence of images taken through
each of MDIS's 11 filters..

Like the previously mapped portion of Mercury, this hemisphere appears
heavily cratered. It also reveals some unique and distinctive features.
On the upper right is the giant Caloris basin, including its western
portions never before seen by spacecraft. Formed by the impact of a
large asteroid or comet, Caloris is one of the largest, and perhaps one
of the youngest, basins in the Solar System. The new image shows the
complete basin interior and reveals that it is brighter than the
surrounding regions and may therefore have a different composition.
Darker smooth plains completely surround Caloris, and many unusual
dark-rimmed craters are observed inside the basin. Several other
multi-ringed basins are seen in this image for the first time. Prominent
fault scarps (large ridges) lace the newly viewed region.

Other images obtained during the flyby will reveal surface features in
color and in much more detail. Collectively, these images and
measurements made by other MESSENGER instruments will soon provide a
detailed global view of the surface of Mercury, yielding key information
for understanding the formation and geologic history of the innermost
planet.

Additional information and features from this first flyby 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 Tue 15 Jan 2008 08:56:14 PM PST