[meteorite-list] Latest MESSENGER Images Show Fascinating Views of Mercury's Surface

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 22 Jan 2008 14:52:36 -0800 (PST)
Message-ID: <200801222252.OAA06011_at_zagami.jpl.nasa.gov>

http://messenger.jhuapl.edu/news_room/status_report_01_20_08.html

MESSENGER Mission News
January 20, 2008

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Latest MESSENGER Images Show Fascinating Views of Mercury's Surface
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MESSENGER Views an Intriguing Crater

MESSENGER's Narrow Angle Camera (NAC) on the Mercury Dual Imaging System
(MDIS) acquired this view
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=127>
of Mercury's surface illuminated obliquely from the right by the Sun.
The unnamed crater (52 kilometers, or 31 miles, in diameter) in the
center of the image displays a telephone-shaped collapse feature on its
floor. Such a collapse feature, not seen on the floors of other craters
in this image, could reflect past volcanic activity at and just below
the surface of this particular crater.

MESSENGER team members are examining closely the more than 1,200 images
returned from this flyby for other surface features that can provide
clues to the geological history of the innermost planet.

The crater is located in the southern hemisphere of Mercury, on the side
that was not viewed by Mariner 10 during any of its three flybys in 1974
and 1975. This scene was imaged while MESSENGER was departing from
Mercury from a distance of about 19,300 kilometers (12,000 miles), about
one hour after the spacecraft's closest encounter with Mercury. The
image is of a region approximately 236 kilometers (147 miles) across,
and craters as small as 1.6 kilometers (1 mile) can be seen.

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Ridges and Cliffs on Mercury's Surface

A complex history of geological evolution is recorded in this frame
<http://messenger.jhuapl.edu/gallery/sciencePhotos/image.php?gallery_id=2&image_id=128>
from the Narrow Angle Camera (NAC), part of the MDIS instrument, taken
during MESSENGER's close flyby of Mercury on January 14, 2008. Part of
an old, large crater occupies most of the lower left portion of the
frame. An arrangement of ridges and cliffs in the shape of a "Y" crosses
the crater's floor. The shadows defining the ridges are cast on the
floor of the crater by the Sun shining from the right, indicating a
descending stair-step of plains.

The main, right-hand branch of the "Y" crosses the crater floor, the
crater rim, and continues off the top edge of the picture; it appears to
be a classic "lobate scarp" (irregularly shaped cliff) common in all
areas of Mercury imaged so far. These lobate scarps were formed during a
period when Mercury's crust was contracting as the planet cooled. In
contrast, the branch of the Y to the left ends at the crater rim and is
restricted to the floor of the crater. Both it and the lighter-colored
ridge that extends downward from it resemble "wrinkle ridges" that are
common on the large volcanic plains, or "maria," on the Moon.

The MESSENGER science team is studying what features like these reveal
about the interior cooling history of Mercury.

Ghostly remnants of a few craters are seen on the right side of this
image, possibly indicating that once-pristine, bowl-shaped craters (like
those on the large crater's floor) have been subsequently flooded by
volcanism or some other plains-forming process.

This image was taken 18 minutes after close approach, when MESSENGER was
about 5,000 kilometers (about 3,000 miles) away from Mercury. The image
is about 200 kilometers (about 125 miles) across, and features as small
as about 400 meters (about 400 yards) can be resolved.

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Additional information and features from MESSENGER's first flyby of
Mercury are online at http://messenger.jhuapl.edu/mer_flyby1.html.

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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 22 Jan 2008 05:52:36 PM PST