RSF@SU-AI@sri-unix.UUCP (08/02/83)
From: Ross Finlayson <RSF@SU-AI>
n533 0224 02 Aug 83
BC-MARS-3takes-08-02
By David L. Chandler
(c) 1983 Boston Globe (Independent Press Service)
Seven years ago in July, a remote-controlled machine about the size
of a VW Rabbit separated itself from an orbiting spacecraft and
descended to a red, rocky plain. It was the Viking 1 lander, first
object from Earth ever to land on Mars.
One of its primary goals was to search for signs of life, using a
set of three biological experiments. Yet seven years after that first
Viking landing, the debate rages on: Did the tests show signs of
life, or just a puzzling set of chemical reactions?
Some scientists say there's strong, convincing evidence for life,
while others are positive that Mars is barren.
The issue is not likely to be resolved until - and unless - there's
another Mars mission. But those who think that life is likely got a
significant boost recently when tests done on Antarctic soil were
found to duplicate the most puzzling of the results from Mars. Both
sets of tests showed evidence of microbial life, in the form of
''respiration'' of gases from the soil, and yet showed no sign of
life's basic building blocks - organic compounds - within that soil.
In short, there is now direct evidence that life forms can exist in
soil without producing enough chemical debris - enough dead bodies -
to be detected by the Viking equipment; that, as one scientist put
it, there can be music even though there's no sign of any
instruments. By resolving the biggest apparent conflict in the Mars
data, this finding has moved some disbelievers into the ''maybe''
camp.
But many still feel that life is unlikely on Mars. Klaus Biemann,
the scientist at Massachusetts Institute of Technology who developed
the Viking test for organic compounds in the soil, says ''the
majority of scientists, both in and out of the Viking team, believe
that the biology experiments were negative, and that they can all be
explained by one non-biological chemical reaction or another.''
Norman Horowitz, a Cal-Tech biochemist who designed one of Viking's
life-detection tests, has put it even more strongly. Writing about
the results of the mission in Scientific American, he said: ''At
least those areas on Mars examined by the two spacecraft are not
habitats of life.''
On the other hand, biochemist Alexander Rich of MIT, who was also a
member of the Viking biology team, said recently: ''It is not correct
to say that Mars has been shown to be lifeless. We failed to
demonstrate that life is there, but we didn't disprove it. It's a
matter of judgment. It certainly warrants going back with a broader
set of experiments to see what's there.''
Probably the strongest believer in the evidence for life on Mars is
Gilbert Levin, president of Biospherics Inc. of Maryland. He was the
chief scientist in charge of the Viking life-detection experiment
that gave the clearest positive results, and he says that ''If you
look objectively at the data, it's more likely than not that we
discovered life.
''People think the Viking tests failed to return any evidence for
life,'' says Levin. ''But in fact, there's a lot of evidence.''
Levin thinks that his experiment, the ''labeled release'' (LR) test,
produced strong evidence for the existence of some kind of microbes -
perhaps resembling Earth bacteria or algae - by measuring
carbon-dioxide discharges from soil that had been moistened with a
nutrient solution.
Levin also has discovered that there are greenish patches visible on
rock surfaces in the Viking photographs, which he thinks might turn
out to be a form of life similar to lichens - one of the hardiest of
living organisms.
And other recent discoveries have also boosted the prospects for
Martian life, prompting Rich, the MIT biochemist, to say, ''I think
the conclusions are vastly different than they were before.''
The announcement this year of the discovery of microbes that survive
at over 500 degrees F. near ocean-floor thermal vents shows that
''Life is really much more adaptive than we had anticipated,'' says
Rich. ''That discovery showed that life can adapt to extremely high
temperature and pressure, so we shouldn't write off Venus (as a
possible habitat for life). I believe this shows that life can adapt
to low temperature and pressure as well.'' On Mars, temperatures
seldom rise above freezing, and the atmospheric pressure is less than
one-hundredth of Earth's.
As for interpreting the Viking results, Levin points out that
despite intensive efforts over the last seven years, no one has yet
come up with a specific set of chemical reactions that can explain
the results of his LR experiment on Mars. If no chemical explanation
can be found, scientists agree, a biological reaction - living
microorganisms in the Martian soil - would be the only way to account
for the data.
The results of Levin's test did in fact meet all the criteria
established before the mission to conclude that life had been
discovered.
First, a substantial positive response - consisting of a release of
gas (probably carbon dioxide) from the soil, as would be expected
from the metabolism of microorganisms such as bacteria or algae - was
obtained from each ''active'' run of the experiment in two different
regions of the Martian surface.
And second, the biological nature of the response was apparently
confirmed by the negative results - virtually no gases produced -
from each ''control'' run, in which the soil was first sterilized by
heat. The control runs were considered a crucial test for determining
whether a response really came from living organisms, since microbes
would be killed by the high temperature and so stop ''breathing,''
whereas most non-living chemical reactions would not be affected by
the heat.
As Viking chief biologist Harold Klein pointed out in his official
summary of the biology test results, ''The LR .-.-. yielded data
which met the criteria originally developed for a positive. On this
basis alone, the conclusion would have to be drawn that metabolizing
organisms were indeed present in all samples tested.''
Since the test met the requirements for a ''presumptive positive,''
why didn't the scientists announce that life had been discovered? And
why do they still disagree on what the results mean?
Levin claims with some annoyance that his fellow scientists
''changed the rules after the results were in. If we had followed the
rules, we would have stood up and said: 'We discovered life.'-''
There were, however, three unexpected aspects of the data that
caused most of the scientists to hold back from saying that the
results indicated life in the Martian soil. One was the fact that the
LR test result, although positive, was very different from the usual
response seen in Earth soils: Instead of the rate of gas production
increasing steadily because the microorganisms multiplied rapidly in
the soil, as happens when Earth soil is tested, the Mars response
gradually leveled off.
Biochemist Cyril Ponnamperuma, editor of the respected scientific
journal Origins of Life, says that because of this leveling off of
the response, the positive result is ''not completely convincing, but
it is tantalizing.''
Another problem was the strange response from another life-detection
test, the Gas-Exchange experiment, which produced an intense, sudden
burst of oxygen when the Martian soil was exposed to moisture. This
result, which everyone agreed looked like a non-living chemical
reaction rather than a lifelike response, suggested to most of the
scientists that there was some kind of highly reactive chemical
compound in the soil, and that perhaps the same compound was
responsible for the LR response.
But by far the greatest stumbling block for a biological
interpretation of the Mars data was the resoundingly negative, and
totally unexpected, result of a test called the GCMS (gas
chromatograph-mass spectrometer). This experiment searched for the
presence in Martian soil of organic (carbon-based) chemicals - the
compounds from which life is made, though they also occur naturally
even in the depths of space. Most people had expected the exact
reverse of the results that were found: That there would be plenty of
organics in the soil, but no reaction from the life tests.
A positive life-test result with no organics seemed impossible, so
there was considerable consternation when the data came in and showed
just that.
But this apparent conflict has now been resolved, claims Levin.
Looking back through published reports on the development of the
experiments used in the Viking mission, he found that a sample of
soil preserved in NASA laboratories, which had been collected from a
dry valley in Antarctica (the environment on Earth that comes closest
to duplicating present Martian temperatures and lack of moisture),
had been tested by both the GCMS and the much more sensitive LR test.
The results of these two independent tests very closely duplicated
the results from Mars.
The tests showed that the soil, Antarctic soil number 726, which
contained a small quantity of living cells, had no organic chemicals
detectable by the GCMS, yet gave a clearly positive result on the LR
test. The seeming discrepancy was apparently nothing more than a
difference in the sensitivity levels of the two tests, says Levin. So
the Martian results of those two experiments, which many biologists
thought were seriously contradictory, have now been demonstrated to
be perfectly compatible.
Biochemist Ponnamperuma was one of those who thought the conflicting
results of these two tests made it very unlikely that they indicated
life on Mars. But when asked last week about Levin's report on the
Antarctic soil, Ponnamperuma exclaimed, ''It's hard to fight that. To
me, that says that it's an open question again.''
In addition to the positive LR test results, another bit of evidence
for Martian life that Levin has discovered is that, contrary to the
first reports from the Viking imaging team, the surface seen in the
photographs of the Martian landscape is not uniformly red. In fact,
there are small greenish patches on some of the rocks and on the soil.
These patches have changed shape and position over the course of a
Martian year (about two Earth years), and they appear to match quite
closely the appearance, color, and thickness of terrestrial lichens,
long thought to be the form of Earth life best adapted for survival
in the cold, dry Martian climate. Levin points out that lichens are
the pioneers of life on Earth, the first living things to appear on
barren rocks. His analysis of the color and the changing shapes of
the patches on Mars has since been confirmed by other NASA scientists.
With so many signs pointing toward at least a possibility of current
life on Mars, why do most scientists continue to speak so negatively
about that possibility?
Levin thinks his colleagues are afraid that ''If we're proven wrong
by the next lander, we'll look foolish.'' But to Levin, the reverse
seems at least as likely: ''It reminds me of the emperor's clothes.
If it does turn out that there are organisms on Mars, people will say
'couldn't these people see?'-''
But there is at least one area of agreement among all those involved
in the Viking mission. As Rich puts it, ''Scientists are not
unanimous about the interpretation of the results - we disagree on
details - but we are all in agreement that we have to go back and do
a more comprehensive set of tests.
''If we proved that there was life there, it would be one of the
great cultural events of this age. The scientific fallout, of course,
would be considerable. If we found another biological system on
another planetary body, my God, there are an infinite number of
questions we could ask. But perhaps the most important thing is that
whenever we address cosmic questions like this, all of a sudden we
see much more clearly that we - Homo sapiens - really are all one.''
END
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