[meteorite-list] Exhumed Rocks Reveal Mars Water Ran Deep

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 27 Jun 2012 09:52:29 -0700 (PDT)
Message-ID: <201206271652.q5RGqTmj019176_at_zagami.jpl.nasa.gov>


Exhumed rocks reveal Mars water ran deep
European Space Agency
27 June 2012

By studying rocks blasted out of impact craters, ESA's Mars Express has
found evidence that underground water persisted at depth for prolonged
periods during the first billion years of the Red Planet's existence.
Impact craters are natural windows into the history of planetary
surfaces - the deeper the crater, the further back in time you can probe.

In addition, rocks blasted out during the impact offer a chance to study
material that once lay hidden beneath the surface.

In a new study, ESA's Mars Express and NASA's Mars Reconnaissance
Orbiter zoomed in on craters in a 1000 x 2000 km region of the ancient
southern highlands, called Tyrrhena Terra, to learn more about the
history of water in this region.

Focusing on the chemistry of rocks embedded in the crater walls, rims
and central uplifts, as well as the surrounding exhumed material,
scientists identified 175 sites bearing minerals formed in the presence
of water.

Tyrrhena Terra

"The large range of crater sizes studied, from less than 1 km to 84 km
wide, indicates that these hydrated silicates were excavated from depths
of tens of metres to kilometres," says Damien Loizeau, lead author of
the study.

"The composition of the rocks is such that underground water must have
been present here for a long period of time in order to have altered
their chemistry."

While the material excavated by impacts appears to have been in close
contact with water, there is little evidence for rocks on the surface
lying between the craters in Tyrrhena Terra having been altered by water.

"Water circulation occurred several kilometres deep in the crust some
3.7 billion years ago, before the majority of craters formed in this
region," says co-author Nicolas Mangold.

"The water generated a diverse range of chemical changes in the rocks
that reflect low temperatures near the surface to high temperatures at
depth, but without a direct relationship to the surface conditions at
that time."

By comparison, Mawrth Vallis, one of the largest identified clay-rich
regions of Mars, displays a more uniform aqueous mineralogy that
indicates a closer link with surface processes.

"The role of liquid water on Mars is of great importance for its
habitability and this study using Mars Express describes a very large
zone where groundwater was present for a long time," says Olivier
Witasse, ESA's Mars Express project scientist.
Contact for further information
Received on Wed 27 Jun 2012 12:52:29 PM PDT

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