[meteorite-list] Meteors Not Water Colored Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:29:50 2004
Message-ID: <200309032333.QAA06755_at_zagami.jpl.nasa.gov>

http://www.eurekalert.org/pub_releases/2003-09/ns-mnw090303.php

Contact: Claire Bowles
claire.bowles_at_rbi.co.uk
44-207-331-2751
New Scientist

Meteors not water coloured Mars
Written by Hazel Muir
New Scientist issue: 6th September 2003

WHY is Mars red? The generally accepted explanation that liquid water rusted
its rocks may be wrong. Lab experiments that mimic the environment on Mars
suggest that the planet's reddish hue came from a dusting of tiny meteors
falling on the surface.

The result is fuelling the debate about whether Mars was ever hospitable to
life. The mineral that gives the planet its colour is a reddish iron oxide.
Until now, astronomers thought that it probably formed in a chain of
chemical reactions as iron in rocks dissolved into pools and rivers on the
warm young planet.

The iron oxidised, precipitated, and was then blown all over the planet. But
Albert Yen of NASA's Jet Propulsion Laboratory in Pasadena, California,
began to doubt this after the Mars Pathfinder mission reached the Red Planet
in 1997. The mission revealed that there is more iron and magnesium in
Martian topsoil than within its rocks. This suggests the minerals actually
came from the small, metal-rich meteors and dust particles that constantly
fall onto Mars, says Yen. Calculations suggest they deposit 5 centimetres of
surface layer every billion years.

If that's the case, Mars might not have been so wet after all. To test
whether this topsoil would have needed water to oxidise and turn red, Yen
exposed metallic iron to ultraviolet light, simulating sunlight, in a
chamber containing gases similar to the Martian atmosphere at temperatures
as low as -60 ¡C. Red iron oxides started to form within a week. No water
was necessary, Yen told this week's meeting of the American Astronomical
Society's planetary science division in Monterey, California. Yen does not
claim water never flowed on Mars - the planet's networks of dry valleys and
channels are good evidence that it did, he says. But flowing water seems to
have played only a small role in weathering the surface. "There is something
of a paradox about Mars," agrees Joshua Bandfield of Arizona State
University in Tempe. His team recently showed that the planet has no large
deposits of carbonates, which should have formed if giant pools of water had
persisted on the surface (New Scientist, 30 August, p 12).

Bandfield suggests that liquid water must have occasionally burst out of the
ground, carving channels and gullies, but that it quickly froze again in the
frigid Martian climate. Although the finding makes the evolution of life on
Mars seem unlikely, Bandfield insists it can't be ruled out: "There appears
to be quite a bit more living going on in the Amazon rainforest than in the
dry valleys of Antarctica. But if the question is whether or not life exists
in either climate, the answer is yes to both." Planetary scientists are
hopeful that NASA's rovers will shed more light on Mars's history when they
arrive at the planet next January. Yen says they should resolve the question
of whether there is enough meteor dust to explain Mars's colour. "I'm
sticking my neck out here and making a prediction- I believe that the Mars
rovers will find nickel in the soil," he told New Scientist. Nickel is
abundant in many meteors but rare in Martian rock.



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http://www.spacedaily.com/2003/030903190022.49of7dpa.html

Mars was coloured by meteorites: scientist
AFP
September 2, 2003

PARIS (AFP) - Laboratory evidence is challenging
theories that Mars' ruddy surface came from a past when the planet
was awash with water, New Scientist says.

Defenders of this hypothesis say Mars' reddish dust came from iron
in rocks that over billions of years dissolved into the planet's oceans,
lakes and rivers.

The iron oxidised and was then deposited all over the Martian surface
thanks to the planet's weather system. It was then left high and dry after
the waters mysteriously disappeared, either receding below ground or
boiling into space.

But US scientist Albert Yen of NASA's Jet Propulsion Laboratory has
assailed this idea, noting a strange discrepancy between Mars' dusty
topsoil and its rocks.

The topsoil has more magnesium and iron than the rocks, according to data
sent back by the 1997 Mars Pathfinder mission.

Yen believes that the dust can only have come from tiny metal-rich debris
that constantly falls onto Mars from space.

According to his calculations, the dustfall is big enough to coat Mars to a
depth of five centimetres (two inches) every billion years.

Yen has tested his theory by exposing metallic iron to laboratory-created
conditions that mimick Mars' sunlight, atmospheric gas and chilly
temperature, New Scientist reports in next Saturday's issue.

He found that red iron oxides began to form within a week -- and no water
was necessary.

Yen agrees that surface water was probably abundant on Mars, but says it
was clearly far less important in weathering the planet's surface than is
conventionally thought.

Three missions -- one from Europe, two from the United States -- are en
route for Mars with the goal of testing its soil for the presence of water and
other essentials for life.

The first probe, the European Space Agency's Mars Express/Beagle 2
mission, is due to arrive on December 25.

Yen told the British science weekly that it was likely the probes would find
nickel in the soil that would back his theory that Mars was coloured red
thanks to space dust. Nickel is abundant in meteors but is rare in Martian
rock.
Received on Wed 03 Sep 2003 07:33:27 PM PDT