[meteorite-list] Mars Odyssey THEMIS Images - April 8-13, 2002

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:50:26 2004
Message-ID: <200204122058.NAA19755_at_zagami.jpl.nasa.gov>

MARS ODYSSEY THEMIS IMAGES
April 8-13, 2002

o Gorgonum Chaos (Released 8 April 2002)
o Uzboi Vallis, Nirgal Vallis, and Luki Crater (Released 9 April 2002)
o Medusae Fossae Formation (Released 10 April 2002)
o Southern rim of Isidis Planitia basin (Released 11 April 2002)
o The so-called "Face on Mars" (Released 13 April 2002)

Note: These images have not been radiometrically nor geometrically calibrated
for this preliminary release. An empirical correction has been performed to
remove instrumental effects. A linear shift has been applied in the
cross-track and down-track direction to approximate spacecraft and planetary
motion. Fully calibrated and geometrically projected images will be released
through the Planetary Data System in accordance with Project policies at a
later time.

NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for
NASA's Office of Space Science, Washington, D.C. The Thermal Emission
Imaging System (THEMIS) was developed by Arizona State University, Tempe, in
collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS
investigation is led by Dr. Philip Christensen at Arizona State University.
Lockheed Martin Astronautics, Denver, is the prime contractor for the
Odyssey project, and developed and built the orbiter. Mission operations are
conducted jointly from Lockheed Martin and from JPL, a division of the
California Institute of Technology in Pasadena.

Image Credit: NASA/JPL/Arizona State University


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Mars 2001 Odyssey
Thermal Emission Imaging System (THEMIS)
Gorgonum Chaos (Released 8 April 2002)

This image shows the cratered highlands of Terra Sirenum in the
southern hemisphere. Near the center of the image running from left to
right one can see long parallel to semi-parallel fractures or troughs
called graben. Mars Global Surveyor initially discovered gullies on the
south-facing wall of these fractures. This image is located at 38°S,
174°W.

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Mars 2001 Odyssey
Thermal Emission Imaging System (THEMIS)
Uzboi Vallis, Nirgal Vallis, and Luki Crater (Released 9 April 2002)

This THEMIS image captures two channels (Nirgal Vallis the smaller sinuous
channel on the left and Uzboi Vallis the larger channel located in the
lower right) and Luki Crater located in the upper right. The mouth of Nirgal
Vallis appears to be truncated by Uzboi Vallis. This indicates that Nirgal
Vallis is an older channel than Uzboi Vallis. The floor of Uzboi Vallis was
subsequently bombarded by an asteroid or comet which gouged out the 21 km
diameter crater named Luki. Luki is named after a town in the Ukraine. Uzboi
is the name of a dry river in Russia. Nirgal is the Babylonian name for Mars.
Gullies and alluvial deposits discovered by Mars Global Surveyor are clearly
visible on the polar-facing (south) wall and floor of Nirgal Vallis and also
in the inner rim of Luki crater. These gullies appear to emanate from a
specific layer in the walls. There is a pronounced sparsity of gullies on
the equator-ward facing slopes but some are present in this image. The
gullies have been proposed to have formed by the subsurface release of water.
The western channel wall of Uzboi Vallis does not appear to have the
fine-scale gullying as does Nirgal Vallis. However, the western channel wall
of Uzboi Vallis does show some evidence of downslope movement (mass wasting).
Some patches of dunes are also seen on the channel floor, notably along the
edges of the channel floor near the canyon walls. There is also a landslide
located along the southern wall of Luki Crater. '

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Mars 2001 Odyssey
Thermal Emission Imaging System (THEMIS)
Medusae Fossae Formation (Released 10 April 2002)

                      The Story

Medusa of Greek mythology fame, the name-giver to this
region, had snaky locks of hair that could turn a person to stone.
Wild and unruly, this monster of the underworld could certainly
wreak havoc on the world of the human imagination. As scary
as she was, Medusa would have no advantage over the fierce,
masterful winds blowing across Mars, which once carved the
streaky, terrain at the top of this image. Wild and whipping,
these winds have slowly eroded away the "topsoil," revealing
ancient craters and other surface features they once covered.
The loosely cemented particles of this "topsoil" are likely made
up of dust or volcanic ash, and are thus more susceptible to
windblown erosion. The Martian winds have actually been
strong and relentless enough over time to strip the land in the
bottom of this image of the material that once covered it, leaving
it hard and bare to the eye.

The Science

This THEMIS visible image was acquired near
7° S, 172° W and shows a remarkable martian
geologic deposit known as the Medusae Fossae
Formation. This Formation, seen here as the
raised plateau in the upper two-thirds of the
image, is a soft, easily eroded deposit that
extends for nearly 1,000 km along the equator of
Mars. In this region the deposit has been heavily
eroded by the wind to produce a series of linear
ridges called yardangs. These parallel ridges
point in direction of the prevailing winds that
carved them, and demonstrate the power of
martian winds to sculpt the dry landscape of
Mars. The Medusae Fossae Formation has been
completely stripped from the surface in the lower
third of the image, revealing a harder layer below
that is more resistant to wind erosion. The easily
eroded nature of the Medusae Fossae Formation
suggests that it is composed of weakly cemented
particles, and was most likely formed by the
deposition of wind-blown dust or volcanic ash.
Several ancient craters that were once
completely buried by this deposit are being
exposed, or exhumed, as the overlying Medusae
Formation is removed. Very few impact craters
are visible on this Formation, indicating that the
surface seen today is relatively young, and that
the processes of erosion are likely to be actively
occurring.

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Mars 2001 Odyssey
Thermal Emission Imaging System (THEMIS)
Southern rim of Isidis Planitia basin (Released 11 April 2002)

                     The Story

Battered and beaten up, the surface of Mars reads like a
history book to geologists, who want to study what has
happened to the red planet over its geological history. Look
for two larger craters diagonal from one another in the
northern part of this image, and then for the smattering of
tinier craters near them. How did these smaller craters come
to be? Did a large meteoroid streak in through the Martian
atmosphere and get broken up as it passed through,
pummeling Mars moments later with its smaller, scattered
pieces? Or were rocks and dirt blasted off the surface when
the two larger craters were formed, only to rain down again on
Mars shortly afterwards? No one quite knows for sure....

Another enigmatic-looking feature is near the left center of
this image. Dark and shadowy-seeming, it looks something
like an exclamation point with the small crater just below it.
Look closely, and you'll see dunes within the large, dark,
blurry patch, which is itself probably composed of moving
sands. Dark, streaky features also appear on the eastern side
of the ridge that runs down the right side of the image,
showing how debris once tumbled down its steepened slopes


               The Science

This image, crossing the southern rim of the
Isidis Planitia basin, displays the contrasting
morphologies of the relatively rough highland
terrain (in the lower portion of the image) and the
relatively smooth materials of the basin (at top).
Upon closer viewing, the basin materials display
an extensive record of cratering, including a small
cluster of craters just north and west of the two
prominent craters in the upper part of the image.
This cluster of craters may represent what are
called 'secondary' craters, which are craters that
form as a result of the ejection of debris from a
nearby impact. Alternatively, these craters may
have formed simultaneously by the impact of
many pieces of a larger meteoroid that broke up
upon entry into Mars' atmosphere. The large
craters in the image are approximately 800
meters (~875 yards) in diameter. Also visible in
the image are dark streaks on the east-facing
side of the north-south trending ridge. These
streaks are likely the result of debris movement
down slope. A dark patch of material is visible at
the left of the image; dark materials are typically
mobile sands, and linear duneforms are apparent
within the dark patch.

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Mars 2001 Odyssey
Thermal Emission Imaging System (THEMIS)
The so-called "Face on Mars" (Released 13 April 2002)

                      The Story

Nature is an imaginative artist, creating all kinds of wonderful
landforms, cloud shapes, and other patterned features that
remind people of familiar things in our lives. We see a "man in
the moon" when it is full in the night sky, and dream of a
dromedary-dotted desert when coming upon Arizona's
Camelback Mountain or Colorado's "Kissing Camels" in the
"Garden of the Gods." Near Ludlow, California, a lonely
prospector once noticed that the appealing outline of the
mountains resembled a reclining woman, and named the place
Sleeping Beauty. And this naming delight isn't limited to
Earth. The Mars Pathfinder mission team couldn't help but
name the rocks at the landing site, including a
bear-headed-looking one named Yogi.

Part of the fun of exploration is not just visiting a strange
world, but relating to it in human terms. On Mars, we've
already seen a valentine heart-shaped crater, a happy-faced
crater, and even a murky and mysterious "face" on Mars. This
face (seen here about halfway down the image and to the
right) is really just a hill with slopes and ridges that are
shadowed in a way that can sometimes resemble a face from
far away. The first picture of this area was taken by the Viking
spacecraft in the 1970s, and people have been intrigued ever
since. However, orbiter camera technologies have actually
become so good in providing a clear view of the hill that it's
almost a disappointment to see how normal an eroded hill this
well-liked feature is. Well, disappointing unless you're a
geologist, that is!

This whole area is, in fact, a geologist's dream. Erosion has
been Nature's sculptor throughout the area, and all kinds of
remarkably shaped knobs and hills speckle the region. While
their shapes are fun to contemplate, it's no mystery to
geologists how they formed. Several flat ledges part way up
the slopes of these hills are made of layers of rock that stand
strong against erosion's relentless carving. Less resistant
layers in the region have eroded away completely in most
places, leaving behind only the small, isolated hills and knobs
we see today. Don't think everything in this scene is easily
understandable, however. What captures the attention of
scientists is a bunch of unusual deposits of material on the
cold, north-facing slopes of the hills. Did Nature mix some
Martian dirt and ice from the planet's "pallet," and then
"paste" on a slightly cemented deposit over the northern
slopes? Or did an upper layer of material slowly creep
downslope over time, carried by the movement of ice? Ground
ice, in this case, has probably been more of a preserver than an
eroder, keeping a record of the formation and existence of
these deposits over time. Geologists are grateful for that peek
into the Martian past and the chance to study it in-depth.

               The Science

The so called "Face on Mars" can be seen
slightly above center and to the right in this
THEMIS visible image. This 3-km long knob,
located near 10° N, 40° W, was first imaged by
the Viking spacecraft in the 1970's and was
seen by some to resemble a face carved into the
rocks of Mars. Since that time the Mars Orbiter
Camera on the Mars Global Surveyor spacecraft
has provided detailed views of this hill that
clearly show that it is a normal geologic feature
with slopes and ridges carved by eons of wind
and downslope motion due to gravity. A
similar-size hill in Phoenix, Arizona resembles
a camel lying on the ground, and Phoenicians
whimsically refer to it as Camelback Mountain.
Like the hills and knobs of Mars, however,
Camelback Mountain was carved into its
unusual shape by thousands of years of erosion.
The THEMIS image provides a broad
perspective of the landscape in this region,
showing numerous knobs and hills that have
been eroded into a remarkable array of different
shapes. Many of these knobs, including the
"Face", have several flat ledges partway up the
hill slopes. These ledges are made of more
resistant layers of rock and are the last
remnants of layers that once were continuous
across this entire region. Erosion has
completely removed these layers in most places,
leaving behind only the small isolated hills and
knobs seen today.

Many of the hills and ridges in this area also
show unusual deposits of material that occur
preferentially on the cold, north-facing slopes. It
has been suggested that these deposits were
pasted on the slopes, with the distinct,
well-defined boundary on their upslope edges
being the highest point of this pasted-on layer.
Alternatively, these unique features could be the
result of the slow downslope motion of the
surface layer, possibly enhanced by the
presence of ground ice. In this model the top
layer of material has separated from the
sub-surface near the crest of the slope and
moved downslope, creating the rounded
boundary seen at the top of the detached layer.
In several cases, such as in the large knob
directly south of the "Face" these deposits occur
at several different heights on the hill, providing
evidence that downslope motion may be the
more likely explanation. In either case, ground
ice likely plays an important role in the formation
and preservation of these deposits because they
only occur on the cold slopes facing away from
the Sun where ground ice is more stable and
may still be present today.

This image is the 13th image in a series of daily
images released by the THEMIS Team.
Received on Fri 12 Apr 2002 04:58:05 PM PDT