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ZL2VAL > ROVERS 04.02.04 13:09l 265 Lines 11921 Bytes #999 (0) @ WW
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Subj: The case for water
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Sent: 040204/1007Z @:ZL2AB.#46.NZL.OC #:35036 [New Plymouth] FBB7.00g
From: ZL2VAL@ZL2AB.#46.NZL.OC
To : ROVERS@WW
The Growing Case for Water on Mars
By Robert Roy Britt
Senior Science Writer
posted: 06:30 am ET
03 February 2004
After more than a century of wild speculation, decades of serious
searching, and years of collecting increasingly compelling evidence,
there is suddenly a scientific and media buzz over whether Mars is a
planet sculpted by water.
Thing is, that question is already answered in the minds of most Mars
experts.
For the first billion years or two, Mars was almost surely warmer and
wetter, most scientists agree. What lingers is a big, multi-part mystery
of what happened to all the water, how long ago it disappeared, and
whether it was around long enough -- and under the right conditions --
to have possibly incubated life.
The latest news -- a previously unheralded mineral called hematite has
been detected by NASA's Opportunity rover -- dribbled out late last week
and over the weekend. It might turn out to be a key moment in Mars
exploration history, but some scientists think it is more likely to
represent just another piece in a huge puzzle of a planet that could
remain largely enigmatic for years to come.
About that hematite
Bob Craddock, science advisor to the under secretary for science at the
Smithsonian Institution, says the twin rovers Spirit and Opportunity are
very important to the exploration of Mars. But he cautions that each
robot is exploring only a tiny bit of the red planet -- akin to covering
a few blocks near your home and calling it Earth. Sweeping conclusions
about the entire Martian world will be difficult.
Hematite is particularly tricky.
"It's not going to tell us anything definitive," Craddock told
SPACE.com, "unless we get really lucky and we're able to put the
hematite into some sort of mineralogical context."
Hematite is common on Earth. It is sometimes used to make jewelry. It's
essentially rust, the stuff that forms when iron is exposed to water and
oxygen. The name comes from the Greek word for blood, and in its
powdered form, hematite is indeed reddish. It gives Mars its overall
ruddy color. (Most of Earth's iron sank to the core when the planet was
young. Being less massive, More of Mars' iron ended up at the surface.)
Encouraging signs
The hematite that interests Mars geologists is gray, however. On Earth,
gray hematite generally forms in places where there has been standing
water or hot springs. But it can also be created by volcanic activity.
"Red and gray iron oxides on Mars are really just different forms of the
same mineral," explains Arizona State University geologist Victoria
Hamilton. "If you ground up the gray hematite into a fine powder it
would turn red because the smaller grains scatter red light."
Opportunity's landing site was chosen for an apparent abundance of gray
hematite. An initial examination by the rover's spectrometer, which
splits invisible infrared light into its various colors and then
analyzes chemical signatures, is encouraging.
"I think the preliminary evidence is consistent with hematite forming at
low temperatures in chemical reactions with water," Philip Christensen,
an Arizona State University geologist who leads the hematite
investigation, said Saturday. That means it might not be the volcanic
variety.
Further investigation is planned and may be underway as you read this.
If Opportunity determines the hematite is filling cracks in rocks, then
geologists might assume it was carried along by groundwater -- a
significant scientific finding, said Craddock, who is a geologist by
training and is not involved in the rover missions. If, however, the
hematite is embedded in layers of ash, then scientists would know it was
generated in a volcanic process; water hunters would be disappointed.
'Weird area of Mars'
It won't be easy to put the hematite into context, Craddock said. What's
found might have formed early in Mars' history, merely adding to a
practically closed case for a wet young planet.
Further, Opportunity's landing site was hand-picked because Christensen
and his colleagues had strong evidence, from orbiting spacecraft, that
hematite was there. Craddock said any discoveries at Meridiani Planum,
the equatorial location where the rover is working, will be akin to a
geologist picking up the strangest rock in a field and trying to draw
broad conclusions from that one rock.
The distribution of hematite near the rover Opportunity's landing site,
from a report in the Journal of Geophysical Research in 2001. The data
was collected by NASA's orbiting Mars Global Surveyor.
Credit: Phil Christensen, ASU
"We're going to find out what this anomalously weird area of Mars is
like, but we're going to have a hard time putting it in the context of
99 percent of the planet."
Opportunity's landing site might be unusual just as Yellowstone National
Park is on Earth. Perhaps the now-barren landscape was once was peppered
with hot springs, scientists speculate. And these warm watery areas
might have served as an incubator for life.
"We're very interested to know if this region could have been like
Yellowstone, with hot springs, so we'll be looking to see if there are
other minerals in the area such as those at Yellowstone," said Joy
Crisp, project scientist for the Mars Exploration Rover Project at
NASA's Jet Propulsion Laboratory.
Water does not mean life, scientists point out, but it is the key
ingredient, and so NASA's mantra for Mars exploration has long been
"follow the water."
Liquid history
If the rovers comes up dry, or if they leave scientists scratching their
heads a bit, Spirit and Opportunity will join a long line of robots that
have added much to the knowledge of Mars without unlocking its biggest
secrets.
NASA's Viking missions in the 1970s were designed to find water and
life, if any existed. The Viking probes did detect evidence of
water ice in the northern polar cap as well as trace amounts of water
vapor in the Martian atmosphere.
Scientists have since concluded that the northern cap is loaded with
water ice. More recently, water ice has been found at the south pole.
And NASA's Odyssey orbiter discovered over the past couple of years
extensive water ice just under the surface away from the permanently
frozen caps.
But organisms as we know them cannot live by ice alone. They need liquid
water, at least now and then, so they can emerge from dormancy to repair
their cells and procreate. Some bacteria on Earth are known to stay
dormant for up to 40,000 years. Other creatures thrive in sub-ice havens
where liquid water exists in pockets, sometimes only briefly.
Perhaps more intriguing than evidence for frozen water, then, are the
countless photographs taken during the past three decades showing
evidence of past rivers, lake and oceans. Collectively the body of
photographs is not entirely conclusive, but few researchers argue that
water long ago scoured the surface of the now-dusty world.
Some scientists cautiously note that the channels and canyons of Mars
might have been formed by lava or flowing carbon dioxide, perhaps even
gaseous carbon dioxide mixed with dust, and not necessarily by water.
Others, particularly those making the investigations, frequently say
that only water could sculpt the features they see.
Craddock, who is dubious of the most recent evidence suggesting water
has carved modest features in recent geologic history -- meaning it
might still flow there -- has little doubt about ancient Mars.
"It's almost undeniable" that there was water in the early history of
the planet, Craddock said.
Flood of evidence
Meanwhile, the spigot of data from Mars has been gushing the past four
years. Here are just a few highlights:
In June of 2000, researchers at Malin Space Science Systems released
pictures from NASA's Mars Global Surveyor showing freshly carved gullies
that appeared to be created by recently flowing water in several dozen
locations. But the Malin scientists admitted their conclusion presented
a perplexing problem: Logic dictated the freezing temperatures at Mars
should have prevented what they saw from happening.
In December of 2000, images from Mars Global Surveyor showed layered
features that suggested ancient lakes. The layering had been seen by the
Mariner missions of the 1970s, but never in such detail. Scientists said the
discovery would be fascinating if it held up, but they admitted it would
be heavily debated.
In 2001, an extensive analysis of Mars data led a team of geologists to
conclude that a vast, ancient reservoir of water in one part of Mars had
sculpted huge gorges and left water trapped in numerous subsurface reservoirs.
That adds to the case for ancient water and helps explain where some of it
might have gone.
And fresh analysis in late 2002 of dark streaks spotted racing down
canyon walls, first noted in the Viking era, suggested to other researchers
that water is still running on Mars, at least in brief spurts.
Then earlier this month, European Space Agency scientists put out one of
the first images from their new Mars Express orbiter. It provided a
high-resolution 3D view of a channel they think was carved by a river long
ago. At the bottom of the channel is a dark region, not a shadow but some sort
of deposit that's been laid down.
"There is no other phenomena that we know of that would produce these
effects," said Gerhard Neukum of Germany's Free University of Berlin.
"It is fair to say we are sure this is evidence of once-flowing water on
the surface of Mars."
Other studies, however, have held that if water sculpted Mars, it
probably did so in brief, hellish periods -- not the sort of conditions prone
to fostering the development and sustenance of life. Supporting this less
glamorous scenario, research last August found a relative dearth of limestone
structures called carbonates that should have been left behind if there were
ever serious lakes or oceans.
Craddock said the lack of carbonates might be easily explained. They're
sometimes hard to detect on Earth, he said, so scientists might simply
not be seeing them on Mars when looking down from orbiting spacecraft.
Also, Mars' thin atmosphere lets in more ultraviolet radiation, which is
known to destroy carbonates.
The real goal
If scientists can find sites that once held water -- ideally places that
were recently wet -- then those might be good locations to send new
missions designed to search for evidence of past or present life, such
as fossils or chemical signatures of biological activity.
(Water would also be useful to future manned missions, both for drinking
and to generate hydrogen, which could be used for fuel on a return flight.)
With all the excitement of late, and some media hype, it might seem
almost inevitable that Mars was once a life-bearing planet. Most
mainstream scientists are very cautious on this point, however. Some are
very doubtful.
"I think it's very unlikely that Mars ever had life," Craddock said. "I
would argue that the evidence for Bigfoot or UFOs is better than for
life on Mars."
He nonetheless supports planned missions that would scour the red planet
for signs of biology, in part because even a failed search, via a bit of
twisted logic, could along the way answer the huge question of how life
began on Earth -- another gaping hole in scientific knowledge.
"If we don't find life, we might find the prebiotic chemistry that went
into life on Earth," Craddock explained. "That's more important, because
we know what life is, but we don't know about the precursor chemistry
that went it."
=========================
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