Mars Express's OMEGA uncovers possible sites for life
http://www.esa.int/SPECIALS/Mars_Express/SEM117OFGLE_0.html

20 April 2006
By mapping minerals on the surface of Mars using the
European Space Agency's Mars Express spacecraft,
scientists have discovered the three ages of Martian
geological history - as reported in today's issue of
Science - and found valuable clues as to where life
might have developed.

The new work shows that large bodies of standing water
might only have been present on Mars in the remote
past, before four thousand million years ago, if they
were present at all. Within half a billion years,
these conditions had faded away.

The results come from the Observatoire pour
la Mineralogie, l'Eau, les Glaces et l'Activite (OMEGA)
instrument on board Mars Express. In one Martian year
(687 Earth days) of operation, OMEGA mapped 90 percent
of the surface, allowing the identification of a
variety of minerals and the processes by which they
have been altered during the course of Martian history.
The maps have allowed a team of scientists, led by
Professor Jean-Pierre Bibring, Institut d'Astrophysique
Spatiale (IAS), Orsay (France), to identify three
geological eras for Mars.

The earliest, named by the authors as the 'phyllosian'
era, occurred between 4.5-4.2 thousand million years
ago, soon after the planet formed. The environment
was possibly warm and moist at this time, allowing
the formation of large-scale clay beds, many of which
survive today.

The second era, the 'theiikian', took place between
4.2 and 3.8 billion years ago. It was prompted by
planet-wide volcanic eruptions that drove global
climate change. In particular, the sulphur these
eruptions belched into the atmosphere reacted with
the water to produce acid rain, which altered the
composition of the surface rocks where it fell.

Finally, there was the 'siderikian', the longest
lasting of the Martian eras. It began sometime
around 3.8-3.5 billion years ago and continues
today. There is little water involved in this era;
instead, the rocks appear to have been altered during
slow weathering by the tenuous Martian atmosphere.
This process gave Mars its red colour.

The eras are named after the Greek words for the
predominant minerals formed within them. The one
most likely to have supported life was the
phyllosian, when clay beds could have formed at
the bottom of lakes and seas, providing the damp
conditions in which the processes of life
could begin.

However, there are still question marks. The team
points out that the clay beds might have been
formed underground, rather than in lakebeds.

"Hydrothermal activity below the surface,
the impact of water-bearing asteroids,
even the natural cooling of the planet
could all have promoted the formation of
clay below Mars's surface. If so, the surface
conditions may always have been cold and dry,"
said Bibring.

After this initial period, water largely
disappeared from the planet's surface either
by seeping underground or being lost into space.
Except for a few localised transient water events,
Mars became the dry, cold desert seen by spacecraft
today. This new identification of clay beds on Mars
provides high-priority targets for future Mars
landers that seek to investigate whether Mars once
harboured life.

"If living organisms formed, the clay material would
be where this biochemical development took place,
offering exciting places for future exploration because
the cold Martian conditions could have preserved most
of the record of biological molecules up to the present
day," concluded Bibring.
http://www.esa.int/SPECIALS/Mars_Express/SEM117OFGLE_0.html

The full results are published in the 21 April issue
of the journal Science.
http://www.sciencemag.org/content/vol312/issue5772/
http://www.sciencemag.org/cgi/content/full/312/5772/400

Science Magazine
http://www.sciencemag.org/magazine.dtl

Mars Express
http://www.esa.int/SPECIALS/Mars_Express/index.html

Mars Reconnaissance Orbiter - Update:
http://marsprogram.jpl.nasa.gov/mro/mission/orbiter_update.h...
http://mars.jpl.nasa.gov/mro/
http://mars.jpl.nasa.gov/