20 September 2006
When it was launched in 1996, the plan was that Mars Global Surveyor (MGS)
would wrap up its mission in 2000. Damage to a hinge connected to a solar
panel slowed the orbit insertion aerobraking process by a year, so in 1997
the spacecraft team determined that MGS's mission would end in early 2001.
However, the spacecraft and its instruments remained healthy, and its
mission was extended. And extended. And extended again. And again. MGS has
now been orbiting the red planet for just over nine years. Throughout the
mission, data from the Mars Orbiter Camera (MOC) have emphasized details
about some of the very oldest and the very newest features exposed on the
planet's surface.
The very ancient and the modern come together in this small, approximately
3 km by 3 km (1.9 mi by 1.9 mi) area on the floor of an unnamed impact
crater in western Arabia Terra.
Old are the light-toned, layered mounds scattered across the image. The
layers form stair-steps leading to the top of each mound. In most cases,
the 'steps' are not clean, but are instead covered with debris eroded from
the next layer, or step, above. The mounds are remnants of layered rock
that once covered the entire scene. They were deposited as sediment in the
large, unnamed crater in which these landforms occur. Their regular
thickness and repeated character suggest that episodic, or perhaps cyclic,
processes brought sediment to the crater floor. If the crater contained
water at the time the sediments were deposited, then they represent
lakebed materials. The processes that (a) brought sediment to this site,
(b) cemented the sediment to form rock, and (c) eroded the sediment to
form the mounds we see today, all occurred at some time in the distant
past.
New are the dark-toned sand dunes and intermediate-toned ripples. The dark
dunes were formed of sand that in relatively recent times has been blown
by wind from the northeast (upper right) toward the southwest (lower
left). The dunes have slowly encroached upon the older, light-toned,
layered mounds. Surrounding each mound is a suite of intermediate-toned
ripples. These are large ripples, relative to counterparts on Earth, and
are most likely made up of grains somewhat coarser than sand, typically of
several millimeters in size. The ripples form a pattern that is generally
radial to each mound, indicating that they formed in winds that interacted
with these topographic obstacles. The dark dunes are generally younger
than the ripples, as dark sand has encroached upon and over-ridden some of
the ripples.
This image is one of the favorites of the MOC operations team at Malin
Space Science Systems, because it is not only pretty, it also emphasizes
aspects of both the ancient and modern sedimentary processes and materials
on Mars. Sediments, sedimentary rocks, and the environments in which they
were deposited have been a key theme of the MOC science investigation from
the beginning, more than 20 years ago, when MOC was selected by NASA to be
built and sent to Mars. The first MOC was aboard Mars Observer when it was
lost in 1993; the second MOC was built for MGS and is still operating
today.
Location near: 8.8°N, 1.2°W
Image width: ~3 km (~1.9 mi)
Illumination from: lower left
Season: Northern Winter