- Mars is one wet and wild world. Scientists are slowly
warming up to the view that trickling amounts of water on the cold, dry
planet may be nourishing Martian biology.
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- Thanks to spacecraft observations by the Mars Global
Surveyor (MGS), newly formed dark slope streaks on Mars have been spotted.
Emanating from a point source, they widen as they flow down slope. In some
cases, they divide into separate streaks as they encounter other surface
features.
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- These sharp-edged dark stains always appear on slopes,
mostly inside craters and valleys, but also on small hills. They are almost
always located below Martian sea level - zero elevation.
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- Over the last few years, cause for the streaks has been
chalked up to the work of winds, or cascading surface materials. These
processes would remove light-colored surface dust to expose darker bedrock
beneath - so the thinking went.
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- Let it flow
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- A new view is that liquid flow is the most promising
process for explaining the dark streaks. They appear to indicate currently
flowing water on Mars.
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- That's the interpretation of Tahirih Motazedian, carrying
out independent undergraduate research at the Department of Geological
Sciences and the University of Oregon.
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- Images snapped by MGS months apart of a same area on
Mars show that new streaks have formed within a time interval of months.
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- "It could have happened in an hour or taken all
of six months," Motazedian said during a presentation of her research
findings at the 34th Lunar and Planetary Science Conference (LPSC), held
March 17-21 in Houston, Texas.
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- Heat source
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- Motazedian said that the dark streaks can be found in
various parts of Mars, but are heavily concentrated in the vicinity of
Olympus Mons - a huge volcano on the red planet. Some form of geothermal
activity on Mars -- acting either to melt subsurface ice or releasing water
from liquid aquifers, or a combination of the two -- is releasing liquid
onto the surface and forms the dark streaks, she said.
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- It is possible, Motazedian suggested, that geothermal
activity, driven by volcanic heat, is melting subsurface ice. This melting,
in turn, releases a brine that dissolves surrounding minerals. Furthermore,
the brine has a low freezing temperature, allowing it to flow at the Martian
surface. The dissolved minerals precipitate from solution, leaving behind
dark streaks of rock varnish.
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- The most exciting thing about dark streaks is that they
are currently forming today, Motazedian told the scientific gathering.
"As I speak to your right now, there are dark streaks forming on Mars.
That,s literally true," she said.
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- Not a dead planet
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- The sharply-defined end-points of the dark streaks, Motazedian
said, implies that the flows end where their liquid source is exhausted,
having been consumed in a coating of surface dust and soaking into the
ground.
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- The dark streaks passively overlay other surface features
on Mars without disturbing them or causing erosion. The dark streaks themselves
have neither positive nor negative relief, Motazedian's research indicates.
They appear as if they are stains on the existing topography, she reported.
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- The amount of water flowing over the surface to create
the streaks appears to be very, very small, Motazedian said. "It's
pretty much soaking or sublimating (vaporizing) as soon as it comes down.
So it's not forceful enough to erode a path for itself," she noted.
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- "Mars is not a dead planet," Motazedian. "So
I'm suggesting that all of you should quit your jobs and investigate dark
streaks," she told the LPSC gathering.
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- Streaks of microbial life
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- Could the dark stains be biological?
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- David McKay, a NASA Center in Houston, aired that prospect
at the LPSC meeting. He is lead analyst in the ALH 84001 Mars meteorite
detective work that suggests the rock sports the telltale signs of past
life on the red planet.
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- McKay offered an alternative view of the dark nature
of the streaks. He speculated that there could be some dormant microbial
life form that is rejuvenated by the water and, therefore, it is dark when
it grows and then slowly dies off over months or years.
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- "I'm suggesting this seriously as an explanation.
I would like to see somebody demolish itbut it seems to me that with our
current data we cannot exclude it," McKay said.
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- Dark dune spots
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- Also at LPSC, a team of Hungarian Mars researchers, led
by Tibor Ganti and Andras Horvath, presented new work based on comparative
MGS imagery taken over an extended time period. They see a tie between
water in Mars' upper layer and the formation of what they call dark dune
spots, or DDSs.
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- They have charted the comings and goings, and rebirth
of the DDSs from 1998 to 2002. In their view, the spots point to "some
kind of biological activity of putative Mars surface organisms, acting
on, or in, the material of the dark dunes."
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- "The massive reappearance of the spots at their
original sites seems to be compatible with our Mars surface organism hypothesis
about the biological origin of dark dune spots," the researchers said.
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- Evidence for water on the red planet documented by the
Mars Odyssey spacecraft has bolstered the beliefs of the Hungarian Mars
team.
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- The prevalence of water seen by Odyssey ranges from the
Mars' South Pole up to 60 degrees South. That coincides with the regions
of the dark dune spots. "From this data we may deduce that water in
some form is relatively abundant in the region of the dark dune spots,"
Ganti and Horvath reported at the LPSC meeting.
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- Mars on ice
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- There is no doubt that Mars is on ice, with huge reservoirs
of frozen water hidden just below the planet's surface.
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- The story of how much ice is sequestered subsurface continues
to grow, said William Boynton of the University of Arizona and principal
investigator for the Mars Odyssey's Gamma Ray Spectrometer.
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- Data gleaned by Odyssey has shown tremendous water ice
deposits, Boynton said.
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- "It really is changing the way we think of how the
ice formed," Boynton told SPACE.com . The idea that water vapor eked
down to depths deep enough and cold enough to condense out does not seem
to account for the vast amounts of water ice detected, he said.
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- There's no telling how deep the ice might extend just
below surface on Mars, Boynton said. It could be several hundreds of feet
to well over a mile in depth.
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- "All of a sudden you're starting to talk about a
pretty significant amount of water," Boynton said. "It looks
like the Viking 2 landing site was actually right on top of this ice. If
its robot arm had dug just a little bit deeper they would have found it,"
he said.
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- As for life being preserved in the ice or still kicking
today, Boynton said that, with reasonable confidence he believes there's
loads of ice on Mars. "If there is something that is happy living
in iceit is going to be very happy there," he said.
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