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. 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.
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. This
computer-generated perspective view of Reull Vallis was created using
data obtained from the High-Resolution Stereo Camera
(HRSC) on ESA’s Mars Express. This perspective view shows a small
tributary channel which, in the wider context view, is seen to later
merge back into the main channel. Strong linear features are clearly
seen on the valley floor in this view, evidence of ice and loose debris
scraping away the floor in a glacial-like manner. The sides of Reull
Vallis are particularly sharp and steep in these images, with parallel
longitudinal features covering the floor of the channel itself.
The color-coded overhead view below is based on an ESA Mars Express
HRSC digital terrain model of the Reull Vallis region, from which the
topography of the landscape can be derived. The color coding shows the
depth of the main channel, coloured in blue, which contrasts clearly
against the Promethei Terra Highlands and their smooth, soft and rounded
mountain tops. The image was taken during revolution 10657 on 14 May
2012.
Similar lineated structures, believed to be rich in ice, can also be
found in many of the surrounding craters. 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 computer-generated perspective view of part of the Promethei
Terra highlands adjacent to Reull Vallis shown below was created using
data obtained from the High-Resolution Stereo Camera (HRSC) on ESA’s
Mars Express. The image shows a rounded and smooth-topped mountain with a
large impact crater in the foreground. The crater is largely filled in
with sediments and shows step-like structures towards the right side,
possibly indicative of sublimation or evaporation of water ice at
different times and at different depths within the crater.
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.
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.
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.
Image credit: Credit: ESA/DLR/FU Berlin (G. Neukum)
Source: The Daily Galaxy via European Space Agency
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