[meteorite-list] Mars Express: Reull Vallis - A River Ran Through It

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 23 Jan 2013 09:12:40 -0800 (PST)
Message-ID: <201301231712.r0NHCeCs004566_at_zagami.jpl.nasa.gov>

http://www.esa.int/Our_Activities/Space_Science/Reull_Vallis_a_river_ran_through_it


Reull Vallis: a river ran through it
European Space Agency
17 January 2013

ESA's Mars Express imaged the striking upper part of the Reull
Vallis region of Mars with its high-resolution stereo camera last
year.

Reull Vallis, the river-like structure in these images, is
believed to have formed when running water flowed in the distant
martian past, cutting a steep-sided channel through the Promethei
Terra Highlands before running on towards the floor of the vast
Hellas basin.

This sinuous structure, which stretches for almost 1500 km across
the martian landscape, is flanked by numerous tributaries, one of
which can be clearly seen cutting in to the main valley towards
the upper (north) side.

[Image]
Perspective view of Reull Vallis

The new Mars Express images show a region of Reull Vallis at a
point where the channel is almost 7 km wide and 300 m deep.

[Image]
Topographic view of Reull Vallis

The sides of Reull Vallis are particularly sharp and steep in
these images, with parallel longitudinal features covering the
floor of the channel itself. These structures are believed to be
caused by the passage of loose debris and ice during the
"Amazonian" period (which continues to this day) due to glacial
flow along the channel.

The structures were formed long after it was originally carved by
liquid water during the Hesperian period, which is believed to
have ended between 3.5 billion and 1.8 billion years ago.

Similar lineated structures, believed to be rich in ice, can also
be found in many of the surrounding craters.

[Image]
Reull Vallis in context

In the wider context image, the tributary intersecting the main
channel appears to be part of a forking of the main valley into
two distinct branches further upstream before merging back into a
single main valley.

The right (northern) part of the main image is dominated by the
Promethei Terra Highlands with their high and soft-rounded
mountains shown in these images, rising around 2500 m above the
surrounding flat plains.

The perspective view below shows one of these mountains with
nearby sediment-filled impact craters.

[Image]
Perspective view of Reull Vallis

This region shows a striking resemblance to the morphology found
in regions on Earth affected by glaciation. For example, we can
see circular step-like structures on the inner walls of the
sediment-filled crater in the foreground of the second perspective
view. Planetary scientists think that these may represent former
high water or glacial levels, before ice and water sublimated or
evaporated away in stages at various times.

[Image]
3D view of Reull Vallis

The morphology of Reull Vallis suggests it has experienced a
diverse and complex history, with analogies seen in glacial
activity on Earth. These analogies are giving planetary geologists
tantalising glimpses of a past on the Red Planet not too
dissimilar to events on our own world today.
Received on Wed 23 Jan 2013 12:12:40 PM PST