Mars Region Probably Less Watery In Past Than Thought, Says Study

http://www.colorado.edu/news/releases/2005/470.html

Mars Region Probably Less Watery In Past Than Thought, Says Study
University of Colorado at Boulder News Release
December 21, 2005

A region of Mars that some planetary scientists believe was once a
shallow lakebed and likely habitable for life may not have been so wet
after all, according to a new University of Colorado at Boulder study.

The new study indicates chemical signatures in the bedrock, interpreted
in 2004 by the Mars Exploration Rover, or MER, mission team as evidence
for widespread, intermittent water at Mars' surface, may have instead
been created by the reaction of sulfur-bearing steam vapors moving up
through volcanic ash deposits. Known as Meridiani Planum, the region
may
have been more geologically similar to volcanic regions in parts of
North America, Hawaii or Europe, said Thomas McCollom of CU-Boulder's
Center for Astrobiology.

"Our study indicates it was probably more like parts of Yellowstone,
Hawaii or Italy than something like the Great Salt Lake," said
McCollom,
also a research associate at CU-Boulder's Laboratory for Atmospheric
and
Space Physics. "We think it was far less favorable for past biological
activity than other scenarios that have been proposed."

A paper on the subject by McCollom and CU-Boulder Research Associate
Brian Hynek of CU-Boulder's LASP appears in the Dec. 22 issue of
Nature.

A series of scientific papers published in December 2004 by the Mars
Exploration Rover team and based on data gathered by the rover
Opportunity, concluded that the Meridiani Planum region once probably
had a large sea or huge lake that may have waxed and waned over eons.
The authors proposed that the evaporation of surface and subsurface
water over time left behind various chemical precipitates --
predominately sulfate salts -- which they interpreted as evidence for a
watery environment that would have been conducive for life to exist.

But if the sulfate was the result of precipitation from an evaporating
brine of surface and subsurface water as has been proposed, McCollom
and
Hynek contend the bedrock should be enriched with a large amount of
positively charged atoms, known as cations, from minerals like iron,
calcium and magnesium. But it is not, they said.

"We think the bedrock was laid down by enormous volcanic ash flows over
time that were then permeated by sulfur dioxide-rich steam vapors,"
said
McCollom. "The sulfur dioxide and water combined to form sulfuric acid,
which reacted with and altered the bedrock to give it its present
chemical composition."

The new scenario does not require prolonged interaction between bedrock
and a standing body of surface water as proposed by the MER team, and
the process likely occurred at high temperatures, perhaps more than 200
degrees F, said McCollom. "Everything about the site seems to be
consistent with our conclusions," he said.

"In our scenario, the water required to support the chemistry in this
bedrock would only have had to have been around for months, years or
perhaps as much as a few centuries," said Hynek. "This is very
different
than previous scenarios, which require that a much larger amount of
water be present for many millennia."'

The European Space Agency's Mars Express spacecraft recently showed the
chemistry of layered deposits surrounding the Meridiani Planum region
is
similar to the bedrock at the Opportunity landing site, implying the
entire area hosted volcanic activity, said Hynek. The size of the
suspected Meridiani Planum volcanic deposits appears much larger than
any similar deposit on Earth and encompasses an area roughly the size
of
Arizona, according to the CU-Boulder researchers.

McCollom described the geology of the region as "solfatara-like,"' a
term that originated from Solfatara Crater, a volcanic region near
Naples, Italy, harboring vents that emit vapors. "While solfataras are
riddled with vents and fissures giving off sulfurous vapors at the
surface, the deposits we see at Meridiani probably represent the
subsurface beneath such fissures," said McCollom.

On Earth, solfataras host microbes that are capable of using sulfur for
sustenance, McCollom said. Some of the areas are now under study by
astrobiologists looking to characterize extreme environments on Earth
that support life.

"My view is that there is a good possibility there is life on Mars,
probably in the subsurface," he said. "We know from examples on Earth
that life can exist in extreme places, and Mars seems to have the
necessary ingredients for that."

Hynek said that in the distant past, Meridiani Planum may have had all
the necessary ingredients to support organisms like those found in
solfataras. "But the unique and probably short-lived nature of the
environment suggests it may not be the best place to look for evidence
of Martian life today," he said.

Contact:

Thomas McCollom, (303) 735-3072
cell phone, (720) 840-7765


Brian Hynek, (303) 735-4312
cell phone, (303) 775-5997


Jim Scott, (303) 492-3114