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Posted by baalke on June 28, 2007, 12:42 pm
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http://www.esa.int/SPECIALS/Mars_Express/SEMF399OY2F_0.html
Tectonic transition zone, Aeolis Mensae
European Space Agency
Mars Express
28 June 2007
The High Resolution Stereo Camera (HRSC) on board Mars Express has
provided snapshots of the Aeolis Mensae region. This area, well known
for its wind-eroded features, lies on a tectonic transition zone,
characterised by incised valleys and unexplained linear features.
Illuminated by the Sun from the west (right side in the image), the
pictures are of a ground resolution of approximately 13 metres per
pixel. The region, imaged on 26 and 29 March 2007, during Mars Express
orbits 4136 and 4247, is located at approximately 6=C2=B0 South and 145=C2=
=B0
East.
[Aeolis Mensae context map]
The morphology of the terrain, which lies close to the volcanic region
of Elysium, is characterised by an extensive transition zone or the
so-called "global crustal dichotomy boundary" which separates the
southern highlands and northern lowlands. It exhibits clod-shaped or
lumpy relief separated by valleys and graben structures, or elongated,
trench-like erosional features.
Aeolis Mensae is located at the border between the northern plains and
the southern highlands, indicated by the transition zone. The area
shown
in the image mosaic is part of the southern highlands and the
transition
zone to the north. Between the highlands and the plains there is a
large
average difference in elevation, of about 3000 metres. The origin of
this dichotomy is currently a subject of discussion.
[Aeolis Mensae North, perspective view]
2500 metre-deep valleys are incised into the highlands in the northern
part of the scene showing linear features on the floor of the valley.
Although the origins are unclear, they may have been created by
glacial
processes, a conclusion drawn from the study of similar glacial
grooves
on Earth. But since the features are orthogonal to the elongation of
the
valley, a glacial origin is unlikely. It is possible that the features
originate due to erosion caused by the wind.
Since the valleys lie close to the transition zone between the
southern
highlands and the northern plains (the crustal dichotomy boundary),
scientists believe that the valleys might originate primarily from
tectonic activity.
[Aeolis Mensae North, perspective view]
Aeolis Mensae is well-known for its features most probably related to
aeolian, or wind-related, activity on the planet's surface and
exhibits
a number of so-called 'yardangs'.
Yardangs are long, irregular ridges with sharp crests that lie between
two round-bottomed troughs carved out by wind erosion in an arid
region.
In this picture, they are more or less linear to streamlined remnants
of
resistant material shaped by the action of sand-blown material which
eroded the weaker material. They can reach a length of several hundred
metres. The direction of the yardangs is from southeast to northwest
indicating the prevalent wind direction.
These structures are also found in deserts on Earth where winds are
the
main agent of change for the landscape. Such features have previously
been observed by Mars Express=E2 HRSC near Olympus Mons on 5 May 2004,
orbit number 143.
[Aeolis Mensae South, perspective view]
If the layered material is more resistant to the action of wind-blown
sands, the landscape can be carved out differently, as can be seen in
the southern and less dissected area of Aeolis Mensae, where
individual
layers become visible.
The images in colour have been derived from the three HRSC colour
channels in combination with the nadir channel. The perspective view
was
obtained from a Digital Terrain Model derived from the HRSC stereo
channels.
[Aeolis Mensae]
The 3D (anaglyph) images were calculated by pulling together data from
the nadir channel and one of the stereo channels. The black and white
high resolution images were derived from the nadir channel, which
provides the highest level of detail.
[Aeolis Mensae North, anaglyph image]
The colour and nadir scenes are a mosaic of pictures derived from
orbits
4136 and 4147. Image resolution has been decreased for easier
downloading.
[Aeolis Mensae South, anaglyph image]
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