http://www.esa.int/esaSC/SEM26D2VW3H_index_0.html
Melas Dorsa reveals a complex geological history on Mars
European Space Agency
5 July 2012
ESA's Mars Express has imaged an area to the south of the famed Valles
Marineris canyon on
the Red Planet, showing a wide range of tectonic and impact features.
On 17 April, the orbiter pointed its high-resolution stereo camera at the Melas
Dorsa
region of Mars. This area sits in the volcanic highlands of Mars between Sinai
and
Thaumasia Plana, 250 km south of Melas Chasma. Melas Chasma itself is part of
the
Valles Marineris rift system.
The image captures wrinkle ridges, some unusual intersecting faults and an
elliptical
crater surrounded by ejecta in the shape of a butterfly and with a strange
"fluid-like"
appearance.
[Image]
Melas Dorsa impact crater perspective view
Elliptical craters like this 16 km-wide example are formed when asteroids or
comets
strike the surface of the planet at a shallow angle.
Scientists have suggested that a fluidised ejecta pattern indicates the
presence of
subsurface ice which melted during the impact. Subsequent impacts have created
a number
of smaller craters in the ejecta blanket.
[Image]
Zoom view of flooded crater
The rim of another large crater is visible in the upper centre part of the
image, but
it appears mostly to have been almost buried during some distant epoch by
volcanic dust
and ash.
This makes any detailed study of it almost impossible. However, its centre shows
concentric deposits that could provide insights into the composition of the
volcanic
material that buried it.
[Image]
Melas Dorsa topography
Several wrinkle ridges can be seen across the image. These form when horizontal
compression forces in the crust pushes the crust upwards.
To the left, the ridges are bisected by crustal displacement faults. These have
cut into
the ridges and the surrounding surface at some later epoch. This highlights the
different
tectonic phases responsible the formation of this region.
[Image]
Melas Dorsa in context
[Image]
Melas Dorsa 3D anaglyph
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