[meteorite-list] Water in a Martian Desert (Mars Express)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 1 Aug 2013 13:25:01 -0700 (PDT)
Message-ID: <201308012025.r71KP1YK014510_at_zagami.jpl.nasa.gov>

http://www.esa.int/Our_Activities/Space_Science/Mars_Express/Water_in_a_martian_desert

Water in a martian desert
European Space Agency
1 August 2013

Craters once brim-full with sediments and water have long since
drained dry, but traces of their former lives as muddy lakes cling
on in the martian desert.

[Image]
Tagus Valles in context

The images were taken on 15 January by ESA's Mars Express, and
feature a region just a few degrees south of the equator within
the ancient southern highlands of Mars. The unnamed region lies
immediately to the north of an ancient riverbed known as Tagus
Valles and east of Tinto Valles and Palos crater that were presented
in an earlier release.

The 34 km-wide crater in the top left of the main images perhaps
draws most attention with its chaotic interior. Here, broad
flat-topped blocks called mesas can be found alongside smaller
parallel wind-blown features known as yardangs.

Both mesas and yardangs were carved from sediments that originally
filled the crater, deposited there during a flood event that
covered the entire scene. Over time, the weakest sediments were
eroded away, leaving the haphazard pattern of stronger blocks behind.

[Image]
Colour-coded topography of Tagus Valles region

Further evidence of this crater's watery past can be seen in the
top right of the crater in the shape of a small, winding river
channel.

Clues also hang onto the ghostly outline of an ancient crater some
20 km to the east (below in the main images). While the crater has
all but been erased from the geological record, a long meandering
channel clearly remains, and flows towards the crater in the
centre of the scene.

This central complex of craters is seen close up in the
perspective view below, showing in more detail another
channel-like feature, along with a highly deformed crater. Perhaps
the rim of this eroded crater was breached as sediments flooded
the larger crater.

[Image]
Deformation in a flooded crater

The crater is also seen from a different angle and in the
background of the second perspective view below. In the foreground
is one of the deepest craters in the scene, as indicated by the
topography map.

Numerous landslides have occurred within this crater, perhaps
facilitated by the presence of water weakening the crater walls.
Grooves etched into the crater's inner walls mark the paths of
tumbling rocks, while larger piles of material have slumped
en-masse to litter the crater floor.

[Image]
Landslides inside a crater

A group of interconnected craters with flat floors smoothed over
by sediments lie in the lower right part of the main image. One
small crater with a prominent debris deposit - an ejecta blanket -
lies within the crater.

Ejecta blankets are composed of material excavated from inside the
crater during its formation. This particular crater exhibits a
"rampart" ejecta blanket - one with petal-like lobes around its
edges. Liquid water bound up in the ejected material allowed it to
flow along the surface, giving it a fluid appearance.

[Image]
Tagus Valles region in 3D

But it's not just water that has played a role in this region;
volcanic eruptions have also had their say. A dark layer of
fine-grained ash covers the top left corner of the main image that
may have been deposited from the Elysium volcanic province to the
northeast. Over time, the ash was redistributed by wind, and
buried deposits exposed in localised areas by erosion.

This region is one of many that exposes evidence of the Red
Planet's active past, and shows that the marks of water are
engraved in even the most unlikely ancient crater-strewn fields.
Received on Thu 01 Aug 2013 04:25:01 PM PDT