New Analysis of Viking Mission Results Indicates Presence of Life on Mars (Forwarded)
Andrew Yee
Washington State University
Pullman, Washington
Contact:
Dirk Schulze-Makuch, WSU School of Earth and Environmental Sciences
509/335-1180
Cherie Winner, WSU News Service
509/335-4846
1/5/2007
NEW ANALYSIS OF VIKING MISSION RESULTS POINTS TO THE PRESENCE OF LIFE ON
MARS
PULLMAN, Wash. -- We may already have 'met' Martian organisms, according to
a paper presented Sunday (Jan. 7) at the meeting of the American
Astronomical Society in Seattle.
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 now -- data 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 -56.5 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 atmosphere -- a valuable trait on a planet where liquid water is
rare.
Schulze-Makuch said that despite hydrogen peroxide's 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 beetle's rear end when the
beetle is threatened.
He said scientists working on the Viking projects weren't 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
conducted.
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 Viking's 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 production --
lower even than the control -- had 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 it's 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 mission's 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 along -- and if we've 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 drowning -- due to
ignorance," said Schulze-Makuch.