[meteorite-list] High Voltage Mars

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon Feb 7 13:19:42 2005
Message-ID: <200502071807.KAA23132_at_zagami.jpl.nasa.gov>

http://www.astrobio.net/news/article1431.html

High Voltage Mars
Astrobiology Magazine
February 7, 2005

Summary: Meteorites and comets should have delivered vast
amounts of organic chemicals to Mars, yet the Viking mission found no
organics in the red soil. A new hypothesis by Sushil Atreya suggests how
dust storms may zap away any chances for life on the martian surface.


High Voltage Mars
by Leslie Mullen

Mars is often enveloped by planet-wide dust storms - their biting winds
choke the air and scour the arid surface. Tornado-like dust devils dance
across the planet so frequently that their numerous tracks crisscross
each other, tracing convoluted designs in the red soil.

Such weather conditions would make life a hardship for any future
explorers on Mars. According to Sushil Atreya, Professor and Director of
the Planetary Science Laboratory at the University of Michigan, these
storms also may have prevented life from ever existing on the martian
surface.

Dust particles in a storm create an electrostatic charge whenever they
strike one another or the ground. In field experiments led by William
Farrell of NASA's Goddard Space Flight Center, electrical fields of 10
kilovolts per meter were measured in dust devils on Earth. Such
experiments suggest that dust devils on Mars could generate very large
electric fields of about 5 to 20 kilovolts per meter.

These electric fields would cause gas molecules in the martian
atmosphere to break down. For example, when the electric fields break
down water vapor (H2O), they would produce hydroxyl radicals (OH).
According to Atreya, these hydroxyls would eventually help form hydrogen
peroxide (H2O2).

The sun probably generates some hydrogen peroxide by photo-dissociating
water vapor in the upper atmosphere. But Atreya estimates the dust
storms might result in 200 times more hydrogen peroxide gas in the
atmosphere than the sun could produce, since most of the water vapor on
Mars is close to the surface - right where the dust storms occur.

"The amount of hydrogen peroxide becomes so large, the atmosphere cannot
hold any more of the gas," says Atreya. "So it begins to snow out of the
atmosphere, and settles on to the surface as hydrogen peroxide dust."

Hydrogen peroxide is a strong oxidant, and would destroy any organic
materials existing on the planet's surface. Since life as we know it is
based on organic chemistry, the hydrogen peroxide dust would snuff out
any chances for such life to appear there.

The lack of organics on Mars was first established by the Viking landers
in 1976. The two landers conducted four experiments to try to detect
life, and one of these experiments showed that the surface of Mars was
entirely devoid of carbon compounds.

Because the thin Martian atmosphere does little to shield the planet
from the harsh ultraviolet radiation of the sun, scientists suspected
that UV light destroyed some of the organics. They also speculated that
oxidizing compounds in the soil, like hydrogen peroxide, also could
destroy organics.

But hydrogen peroxide had never been detected on Mars. That changed in
2003, when two groups detected small amounts of hydrogen peroxide in the
martian atmosphere. Atreya is a member of the Infrared TEXES
spectrometer team, and he says they measured 20 to 50 parts per billion
of hydrogen peroxide using NASA's Infrared Telescope Facility in Hawaii.
Hydrogen peroxide also was detected by a team led by Todd Clancy of the
Space Science Institute in Boulder, Colorado, using the James Clerk
Maxwell Telescope in Hawaii.

But, says Atreya, the amount of hydrogen peroxide detected on Mars is
not enough to remove all the organics that should be on the surface.
Even if there were no indigenous organics on Mars, substantial amounts
of organic material should have been delivered to Mars by the many
meteorites and comets that have impacted the planet since the early days
of the solar system. Large amounts of hydrogen peroxide or another
superoxide produced by dust storms could explain why the surface of Mars
is so barren today.

However much hydrogen peroxide is produced by dust storms, the sun's UV
rays would ensure it would not last long in the air, breaking the
molecules down after a few days. But if hydrogen peroxide ice particles
are bound to the dust particles they ride on, they could mix with the
surface soils after they fall out of the atmosphere, allowing them to
persist in the environment for much longer. This longer residence time
would allow the hydrogen peroxide snow to eventually be converted into
other superoxides by surface chemistry.

If water is mixed in with the soil, or if there is sub-surface ice, the
hydrogen peroxide eventually would combine with this water. Depending on
the concentration of H2O2, this would lower the freezing point of the
water, just as salt makes ocean water less apt to freeze on Earth.

Thus, while hydrogen peroxide on the martian surface would reduce the
chance for life above ground, its presence in subsurface martian water
would increase the odds that life could exist beneath the surface.

The dust storms block our view of what is happening on Mars, so to prove
the storms really are generating hydrogen peroxide, Atreya says a
measuring device would have to be sitting on the surface.

"Surfaces are hard to detect with remote sensing, especially the
localized chemicals," says Atreya. "Also, the hydrogen peroxide would be
mixed in with the regolith, making remote observations of it even more
difficult."

The Mars Rovers Spirit and Opportunity have been traveling on the
martian surface for over a year, but they are not equipped to detect
hydrogen peroxide or other superoxides. Atreya says that the Mars
Science Laboratory (MSL) mission, scheduled for 2009, will include a
suite of instruments that are expected to measure the presence of
superoxides such as hydrogen peroxide.

"This idea is new, and possibly very important," says Mike Mumma,
Director of the Center for Astrobiology at NASA's Goddard Space Flight
Center. "It suggests there should be abundant oxidants on dust
particles. If it bears out, it could provide a very efficient way for
destroying organic compounds much more rapidly than by photochemistry."
Received on Mon 07 Feb 2005 01:07:18 PM PST