[meteorite-list] Mars Water Assumptions May Be All Wet

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Dec 21 14:33:14 2005
Message-ID: <200512211931.jBLJVfC13827_at_zagami.jpl.nasa.gov>

http://space.com/scienceastronomy/051221_mars_dry.html

Mars Water Assumptions May Be All Wet
By Robert Roy Britt
space.com
21 December 2005

The apparent discovery of ancient salty lakes or seas on Mars by NASA's
Opportunity rover last year is viewed as one of the most significant
developments in planetary science.

But two new studies throw some seriously cold water on the whole scenario.

Rather than abundant surface water over significant stretches of
planet's history, as the rover scientists concluded, Opportunity's
observations might represent the results of a meteor impact or volcanic
activity on an otherwise very dry world.

The counter arguments, presented in two papers in the Dec. 22 issue of
the journal Nature, go to the very heart of the ultimate question about
Mars: Was it ever warm and wet enough to support life?

Multiple explanations

At Meridiani Planum, Opportunity found photographic evidence of layered
sandstone that, when analyzed by chemical sensors, looked like it must
have formed in the presence of significant amounts of standing water.

But the deposits could be nothing more than volcanic ash altered by very
small amounts of acidic water and sulfur dioxide, which is a volcanic
gas, argue Thomas McCollom and Brian Hynek of the University of Colorado
at Boulder.

"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," Hynek said today. "This is very
different than previous scenarios, which require that a much larger
amount of water be present for many millennia."'

"This scenario does not require prolonged interaction with a standing
body of surface water," the researchers write.

The Meridiani region was probably more like volcanic parts of
Yellowstone, Hawaii or Italy than something like the Great Salt Lake,
McCollom said. "We think it was far less favorable for past biological
activity than other scenarios that have been proposed."

If McCollom and Hynek's scenario is correct, its effect would be in
"greatly reducing the possibility that these rocks indicate that a
habitable environment ever existed at Meridiani," according to Mark
Bullock, a scientist at the Southwest Research Institute who was not
involved in the studies.

Or it could be?

In the second paper, another group says an impacting space rock can
explain the chemicals and layered deposits observed at Meridiani, as
well as the infamous BB-sized spheres dubbed blueberries.

In fact, write Paul Knauth of Arizona State University and colleagues,
the blueberries are just too spherical and of uniform size to be
explained by formation in water.

Knauth's team proposes that the meteorite generated a "ground-hugging
turbulent flow of rock fragments, salts, sulfides, brines and ice,"
leaving deposits that were later weathered by small amounts of water
embedded in the grains.

The scenario "can account for all of the features observed without
invoking shallow seas, lakes or near-surface aquifers," the scientists
contend.

There is little doubt that Mars, in its early history, experienced bouts
of intense flooding that involved water. The evidence is plainly carved
into the planet's surface in the form of canyons bigger than any on
Earth. But Bullock said those early episodes could have involved very
sudden and short-lived floods spurred by ice melting in meteorite
impacts that would have been frequent when the solar system was young.

"Both groups propose scenarios that preclude the existence of
significant bodies of water at the surface (at least at Meridiani), and
therefore that Mars may never have had conditions conducive to life,"
said Bullock, who wrote an analysis of the work for Nature. "This
conclusion stands in sharp contrast to the provocative interpretations
that there must have been long-lived surface water to form the Meridiani
outcrops."

It will take time for scientists to settle this important debate. The
outcome could effect decisions about where to send future missions that
would search for signs of life. Bullock called the investigation vital,
"whatever the ultimate verdict proves to be."
Received on Wed 21 Dec 2005 02:31:40 PM PST