BOSTON - If there was life in surface
water on Mars early on, it might have enjoyed a very buoyant, salty ride, if it
could thrive in such a hostile environment at all, new research suggests.
Minerals in
sedimentary rocks found at Mars' Meridiani Planum by NASA's Opportunity rover
suggest they formed in extremely
salty water, even saltier than the oceans on Earth, said Andrew Knoll of Harvard University, who is part of a team of scientists taking a closer look at the
geological data collected by the Mars Exploration Rovers mission.
Water was
definitely present at least for short periods of time at Meridiani Planum, he
said, but no one has known how habitable it might have been nor whether it was
around long enough for life to take hold and endure.
So Knoll
and his colleagues looked at data that reveal the chemistry of the salts in the
rocks there as a gauge of the salinity of the ancient water. That allowed the
scientists to estimate how salty the brines were at the time the minerals were
deposited.
"The
punchline is it was really salty," Knoll told a gathering of reporters
here at the annual meeting of the American Association for the Advancement of
Science, "salty enough that only a handful of terrestrial organisms would
have a ghost of chance of surviving there when conditions were at their best."
Constrains
the possibilities
There are a
couple dozen organisms on Earth that can tolerate the salinity levels
determined by Knoll and his team to have been present when the Meridiani Planum
rocks were deposited, he said.
The
research, to be presented today in detail to scientists as well, is currently
under review at a top research journal, Knoll said.
Knoll and
his colleagues also have found several different classes of minerals that
reveal how little the rocks at Meridiani Planum were altered since they were
exposed to the elements, he said. Water at this location was "rare and
transient," according to the research, detailed in an online paper in the Journal
of Geophysical Research — Planets.
The best
era during which to look for evidence
of Martian life would be in Mars' earliest history, Knoll said, that is,
during the first 500 million to 600 million years, before the Meridiani Planum
rocks were deposited.
The new
findings bring scientists no closer to determining whether there was ever microbial
life on Mars, but they do "constrain our thinking about life on
Mars," Knoll said, painting a picture of an environment that is very
"forbidding" for life.
Double
whammy
Previously,
Mars mission data have revealed that liquid water at Meridiani Planum was very
acidic.
"So
it is doubly bad if it's acidic and salty," Knoll said.
"I'm
not sure the effects are necessarily additive, but certainly there are limits
to the physiological ways that microorganisms can adapt to tolerate acidity,"
he said. "There are also limits to ways that they can adapt to tolerate
highly saline environments and those are completely different physiological
systems. In a sense, it makes it harder to adapt that there are two biochemical
systems that would need adapting."
Scientists
are more optimistic that life might have had a chance on Mars in its early
history compared to later on. In earlier times, Mars' environment was probably
wetter, less oxidizing (a condition that is challenging for most life) and less
acidic, but "that doesn't mean it was terrific. It just wasn't as bad as
it got later," Knoll said.
Meanwhile,
Mars scientists and mission engineers gathered at the AAAS meeting today also looked
forward to the May 25 arrival of NASA's Phoenix Lander at Mars' north pole and
discussed work on the Mars Science Laboratory (MSL) mission, set to launch in
September 2009.
MSL will
carry a new rover to Mars
that is far more complex and sophisticated, and five times heavier, than each
of the MER rovers on the red planet now. The MER rovers are learning more about
the habitability of the planet in the distant past, said Richard Cook, MER project
manager.
Instruments
on MSL will focus on detecting organic material at the planet and collecting
more precise data on the minerals at Mars.
As for the
MER rovers, Spirit is hunkered down for winter, parked on a north-facing slope
and serving as a weather station to monitor a nearby dune field. And
Opportunity is descending down the wall of Victoria Crater, investigating its
finely layered rock stacks, made mostly of sulphate salts, said Steve Squyres
of Cornell University, head of the science team for the MER mission.
The rovers
nearly died last summer during intense dust storms on Mars that nearly stole
all their ability to gather power, but they again outperformed expectations and
endured. In fact, it looks good for them to be operational when Phoenix arrives in late spring.
"The
rovers have lasted so long that I am never willing to make predictions about
how long these things will last," Squyres said. "... It's been four
years. You do the math. I think it's pretty likely."
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