[FPSPACE] Did Viking find Martian life - and kill it?
ljk4 at msn.com
Mon Jan 8 00:38:16 EST 2007
Viking Mission Results Indicates Presence of Life on Mars
We may already have met Martian organisms, according to a paper presented
Sunday (Jan. 7) at the meeting of the American Astronomical Society in
Dirk Schulze-Makuch of Washington State University and Joop Houtkooper of
Justus-Liebig-University, Giessen, Germany, argue that even as new missions
to Mars seek evidence that the planet might once have supported life, we
already have data showing that life exists there nowdata from experiments
done by the Viking Mars landers in the late 1970s.
I think the Viking results have been a little bit neglected in the last 10
years or more, said Schulze-Makuch. But actually, we got a lot of data
there. He said recent findings about Earth organisms that live in extreme
environments and improvements in our understanding of conditions on Mars
give astrobiologists new ways of looking at the 30-year-old data.
The researchers hypothesize that Mars is home to microbe-like organisms that
use a mixture of water and hydrogen peroxide as their internal fluid. Such a
mixture would provide at least three clear benefits to organisms in the
cold, dry Martian environment, said Schulze-Makuch. Its freezing point is as
low as -56.5o C (depending on the concentration of H2O2); below that
temperature it becomes firm but does not form cell-destroying crystals, as
water ice does; and H2O2 is hygroscopic, which means it attracts water vapor
from the atmospherea valuable trait on a planet where liquid water is rare.
Schulze-Makuch said that despite hydrogen peroxides reputation as a
powerful disinfectant, the fluid is also compatible with biological
processes if it is accompanied by stabilizing compounds that protect cells
from its harmful effects. It performs useful functions inside cells of many
terrestrial organisms, including mammals. Some soil microbes tolerate high
levels of H2O2 in their surroundings, and the species Acetobacter peroxidans
uses hydrogen peroxide in its metabolism.
Possibly the most vivid use of hydrogen peroxide by an Earth organism is
performed by the bombardier beetle (Brachinus), which produces a solution of
25 percent hydrogen peroxide in water as a defensive spray. The noxious
liquid shoots from a special chamber at the beetles rear end when the
beetle is threatened.
He said scientists working on the Viking projects werent looking for
organisms that rely on hydrogen peroxide, because at the time nobody was
aware that such organisms could exist. The study of extremophiles, organisms
that thrive in conditions of extreme temperatures or chemical environments,
has just taken off since the 90s, well after the Viking experiments were
The researchers argue that hydrogen peroxide-containing organisms could have
produced almost all of the results observed in the Viking experiments.
Hydrogen peroxide is a powerful oxidant. When released from dying cells,
it would sharply lower the amount of organic material in their surroundings.
This would help explain why Vikings gas chromatograph-mass spectrometer
detected no organic compounds on the surface of Mars. This result has also
been questioned recently by Rafael Navarro-Gonzalez of the University of
Mexico, who reported that similar instruments and methodology are unable to
detect organic compounds in places on Earth, such as Antarctic dry valleys,
where we know soil microorganisms exist. The Labeled Release experiment,
in which samples of Martian soil (and putative soil organisms) were exposed
to water and a nutrient source including radiolabeled carbon, showed rapid
production of radiolabeled CO2 which then leveled off. Schulze-Makuch said
the initial increase could have been due to metabolism by hydrogen
peroxide-containing organisms, and the leveling off could have been due to
the organisms dying from exposure to the experimental conditions. He said
that point has been argued for years by Gilbert Levin, who was a primary
investigator on the original Viking team. The new hypothesis explains why
the experimental conditions would have been fatal: microbes using a
water-hydrogen peroxide mixture would either drown or burst due to water
absorption, if suddenly exposed to liquid water. The possibility that the
tests killed the organisms they were looking for is also consistent with the
results of the Pyrolytic Release experiment, in which radiolabeled CO2 was
converted to organic compounds by samples of Martian soil. Of the seven
tests done, three showed significant production of organic substances and
one showed much higher production. The variation could simply be due to
patchy distribution of microbes, said Schulze-Makuch. Perhaps most
interesting was that the sample with the lowest productionlower even than
the controlhad been treated with liquid water.
The researchers acknowledge that their hypothesis requires further
exploration. We can be absolutely wrong, and there might not be organisms
like that at all, said Schulze-Makuch. But its a consistent explanation
that would explain the Viking results.
He said the Phoenix mission to Mars, which is scheduled for launch in
August, 2007, offers a good chance to further explore their hypothesis.
Although the missions experiments were not designed with peroxide
-containing organisms in mind, Phoenix will land in a sub-polar area, whose
low temperatures and relatively high atmospheric water vapor (from the
nearby polar ice caps) should provide better growing conditions for such
microbes than the more tropical region visited by Viking. Schulze-Makuch
said the tests planned for the mission, including the use of two microscopes
to examine samples at high magnification, could reveal whether we had the
answer all alongand if weve already introduced ourselves to our Martian
neighbors in a harsher way than we intended.
If the hypothesis is true, it would mean that we killed the Martian
microbes during our first extraterrestrial contact, by drowningdue to
ignorance, said Schulze-Makuch.
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