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New research by the University of
Leicester and The Open University into evidence of water on Mars,
sufficiently warm enough to support life, has been published this
week in the journal Earth and Planetary Science Letters.
The study determined that water
temperatures on the Red Planet ranged from 50°C to 150°C. Microbes
on Earth can live in similar waters, for example in the volcanic
thermal springs at Yellowstone Park, the scientists behind the
research point out.
Dr John Bridges, Reader in Planetary
Science in the University of Leicester Space Research Centre and Lead
Author, said: "Rovers on Mars – the Mars Exploration rovers
Spirit and Opportunity, and the Mars Science Laboratory rover
Curiosity – are studying rocks to find out about the geologic
history of the Red Planet. Some of the most interesting questions are
what we can find out about water, how much there was and what
temperature it might have had.
"While the orbiters and rovers are
studying the minerals on Mars, we also have meteorites from Mars here
on Earth. They come in three different groups, the shergottites, the
nakhlites and the chassignites. Of most interest for the question of
water on Mars are the nakhlites, because this group of Martian
meteorites contains small veins, which are filled with minerals
formed by the action of water near the surface of Mars."
Dr. Bridges and his group studied those
alteration minerals in great detail. Altogether eight nakhlite
Martian meteorites are known, and all have small but significant
differences between them and in their alteration minerals.
Lafayette is one of them; and the most
complete succession of newly formed minerals can be found in its
veins (see figure). Careful investigations of the minerals with an
electron microscope and a transmission electron microscope have
revealed that the first newly formed mineral to grow along the walls
of the vein was iron carbonate. The carbonate would have been formed
by CO2-rich water around 150°C. When the water cooled to 50°C, it
would have formed the clay minerals, which were then followed by an
amorphous phase that has the same composition as the clay.
Microbes use the reactions during
mineral formation to gain energy and elements essential for their
survival.
Dr Bridges added: "The
mineralogical details we see tell us that there had been high carbon
dioxide pressure in the veins to form the carbonates. Conditions then
changed to less carbon dioxide in the fluid and clay minerals formed.
We have a good understanding of the conditions minerals form in but
to get to the details, chemical models are needed."
Dr Susanne Schwenzer, Postdoctoral
Research Associate in the Department of Physical Sciences at The Open
University who previously studied Martian meteorite compositions,
said: "Until John's study was finished, I used the findings from
orbiters around Mars, and modelled each of the new minerals
individually. Those orbiters have found clays on the surface of Mars,
but the spatial resolution is very different from the detailed study
achieved in the nakhlites. Before we had the detailed study of the
nakhlite meteorites, we did not know that carbonates are forming
first, followed by the clays. Therefore I was very excited to see the
details of the new mineralogical study."
By combining data from both
universities, researchers were able to predict water conditions on
Mars. Initially, the water was around 150°C and contained a lot of
CO2, forming the carbonates, then cooled to about 50°C, thus forming
the clays.
"The driving force heating the
water might have been an impact into the Martian surface." Dr.
Bridges explains. "And you only have to look at a map of Mars to
see how numerous those are on the Martian surface," Dr.
Schwenzer adds.
Image of the Lafayette meteorite
available from pressoffice@le.ac.uk
1. Bridges J.C. and Schwenzer S.P. The
nakhlite hydrothermal brine on Mars.Earth and Planetary Science
Letters 359 (2012) 117.
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