[meteorite-list] Answers My Be Locked Inside Martian 'Bedrock'

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:31:19 2004
Message-ID: <200402021829.KAA19181_at_zagami.jpl.nasa.gov>

http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2004/02/02/MNG9T4MSHM1.DTL
         
Answers may be locked inside Martian 'bedrock'
Keay Davidson
San Francisco Chronicle
February 2, 2004

By a stroke of luck, the Mars rover Opportunity landed literally a
stone's throw away from a scientific gold mine.

Its primary task now will be to explore a rock outcropping that
appears to be Martian "bedrock,'' primeval rock that has been there
since it formed. In images transmitted to Earth, the outcropping
resembles the horizontal layers of rock familiar to any terrestrial
hiker who, wandering through a valley, spies bedrock exposed by
erosion or landslides.

On Earth, exposed bedrock is a window into the deep past, into
geological events that occurred millions of years ago. And the same
should be true on Mars.

"Bedrock is supremely important to a geologist -- 'bedrock' meaning
'rock in place,' rock that hasn't moved much since it was formed,"
said Allan H. Treiman of the Lunar and Planetary Institute in Houston.
Bedrock helps geologists understand "the large-scale structures and
processes" of geological history.

The great thing about bedrock is its stability. It's been sitting in
the same place for eons, unlike other geological debris that has been
scattered far and wide by wind, water, volcanic eruptions and
meteorite impacts.

"In order to understand the chemistry and geological history of Mars,
we need to study rocks that show the fewest signs of weathering," says
Darby Dyar, a space scientist at Mount Holyoke College in
Massachusetts.

"Any loose sediment or boulder, by definition, has been freed from
bedrock by either chemical or physical weathering processes, and
therefore is likely to have been altered since its formation. Access
to bedrock gives us a chance at analyzing unaltered rocks.''

Previous Mars landers saw no "obvious bedrock" on Mars, said Joy A.
Crisp, a project scientist with the Mars Exploration Rover Project at
Jet Propulsion Laboratory in Pasadena. "There were some hints of
possible bedrock at Viking Lander 1 (which landed in 1976), but we
couldn't reach it with the robot arm."

Could the so-called bedrock contain clues of an ancient streambed? Any
youngster who has wandered in a prehistoric streambed has noticed its
smoothed pebbles, rounded down by millennia of tossing and turning in
the current. Hence, if all goes as planned, then Opportunity would
search the rock outcropping for pebbles and other telltale clues to
Mars' possibly aquatic past.

For decades, scientists have debated whether water played a
significant role in molding the surface features of Mars. Powerful
evidence has been presented by both sides. Experts have quarreled over
the meaning of stunning space photos of features that resemble dried
riverbeds, shorelines, floodplains and water-carved canyons, some far
grander than the Grand Canyon.

"In a way, this is still Percival Lowell's ghost haunting us," Treiman
said, referring to the astronomer who, circa 1900, claimed to see
artificial "canals" on Mars.

The debate has become one of the great paradigm squabbles in the
history of geology, akin to a psychologist's Rorschach test, which
looks like a duck to some people, and to others like a rabbit.

"There is no question that there is a lot of water (ice) on Mars,"
said a leading authority on Mars geology, Mike Carr of the U.S.
Geological Survey in Menlo Park. "The main issue is, was it ever warm
enough for liquid water to be stable at the surface?" The data is
conflicting, he says.

Stanford geologist and Mars expert Norm Sleep is confident that
flowing water once existed on Mars. "There are channels that clearly
indicate flowing water. There are also 'bathtub rings' that look
(like) high shorelines," similar to such rings -- formed by long-term
variations in water levels -- on shorelines near Salt Lake City.

The dispute, like many great scientific disputes, tends to divide
along disciplinary grounds.

"Geomorphologists (geologists who study landforms) have always
advocated an early wet Mars, because they can clearly see its effects
in shaping the Martian surface," observes Harry T. ("Hap") McSween, a
member of the Mars rover science team who is directly involved in
assessing the Opportunity landing site.

By contrast, "geochemists (geologists who study the chemistry of
rocks) have tended to favor a dry Mars, because the Martian meteorites
are lavas that are dry as a bone."

Satellite data has detected strong evidence of water ice at the
Martian poles. But was Mars ever warm enough for that ice to thaw into
flowing water? The debate divides into advocates of a "warm, wet" Mars
and a "cold, wet" Mars. If Mars was once warm as well as wet, then
life might have emerged on its surface; but if it was always cold,
then the odds for life would seem to be much weaker.

Treiman complains that NASA and the media have prematurely hyped the
possibility of a warm, wet Mars. True, he acknowledges, "on Mars'
surface, there are several large flood channels, like Ma'adim Valles
that goes through Gusev Crater, and Ares Valles that drains across the
Mars Pathfinder site. These channels look like they carried water only
occasionally as super- humongous floods."

But, Treiman continues, the case for a dry Mars is strengthened by
Martian meteorites, which wandered to Earth after impact events
knocked them off Mars. Chemical analysis of one class of these
meteorites, known as nakhlites, reveals they "formed from molten lava
about 1.3 billion years ago (on Mars)," Treiman says. "Since then,
they were permeated with liquid water exactly once, at about 700
million years ago.

"I have no idea how to reconcile that fact with the happy-face idea of
a warm, wet Mars," Treiman says.

Treiman fumes over recent media coverage of the Mars missions. "There
has been so much nonsense published recently about Mars (not, by far,
all the fault of the media)," he said in an e-mail. He cites one wire
service's report that "the cross-bedding in bedrock of the Opportunity
site (if it's real) means that the rocks were formed from liquid
water.

"This is a 'Geology 101' gaffe," Treiman continued. "Cross-bedding can
form in water-deposited sediments, and in wind-blown sediments (which
is the most common place it's found), and in volcanic tuffs, and (I
expect) in deposits from impact craters."

Treiman lays much of the blame at the feet of NASA politics. "Water on
Mars is such a big thing at NASA that anything can be sold if it
somehow means water and possibly life," he said.

If Opportunity continues to function well, then contested hypotheses
about Mars' geological history could soon be verified or destroyed.

"A lot of people are going to be wrong in some small or large way --
me included! And some are going to be right, too," says Nick Hoffman,
a geologist and Mars expert at the University of Melbourne. Several
years ago, he proposed the controversial idea that Martian surface
features were carved by liquefied carbon dioxide, not by water.

"All geologists are enthused and excited by the presence of bedrock"
on Mars, Hoffman said. "For the first time ever, we have access to a
sample of bedrock on Mars. We never found bedrock on the Moon despite
all the Apollo missions. ... Here (on Mars) is an unequivocal exposure
of genuine rock, rooted firmly in the ground."

"This material is bedded and pale," Hoffman continued. "It's what we
desperately want to understand about Mars -- just what is this pale
rock? Is it a sediment or a volcanic ash? What is the relationship
between the pale rocks and the dark dust? What were conditions like
when it was deposited?

"Frankly, (even) if Opportunity never gets out of this crater, it has
paid off."
Received on Mon 02 Feb 2004 01:29:53 PM PST