The history of astronomy and the search for life elsewhere in the universe is littered
with unexplained detections hidden in obscurity, any one of which may
constitute the discovery of alien life. The problem is with every one of them,
there was some kind of ambiguity present that prevented them from being hailed as
the greatest discovery in human history, instead they sit in a gray basket of maybe, maybe not.
One of the biggest of these mysteries is noteworthy in that it was not a distant
technosignature candidate, or a radio signal, rather it was a detection by an experiment
specifically designed to look for microbial life on Mars. It happened a long time ago,
in this case 1976, a time when Carl Sagan dominated the science popularizer landscape
and when yours truly was still learning how to speak, and had not yet begun to learn
to write. I doubt my parents at the time could have predicted where that would go.
But this case it’s worth a revisit in a modern sense because of my past history with the subject,
and that it’s being called back into the modern debate of whether there may be life on Mars
to the point that it’s being reassessed and may play a major role in the future
exploration of Mars. The experiments actually consisted of four types of
experiments mounted on the Viking landers. Viking one was near the Martian equator,
and Viking two further north, and both had scoops to take soil samples for the experiments.
The first experiment was a gas chromatograph - mass spectrometer. This one measured gas released
when the soil was heated to see what molecules were present. This experiment was important to
the detection overall in a negative way, because it detected very, very little in the way of
organic molecules. In fact, it showed less carbon compounds than the surface of the moon in the
Apollo samples. For decades, this was the primary measurement that cast doubt on the findings of
another of the experiments. This has changed rather dramatically, more on that in a bit.
The next experiment was the Gas Exchange Experiment. It replaced the martian atmosphere
in the sample container with inert helium to see what gases were coming out of the sample
when heated. In this case however, nutrients were added to the soil to see what came out,
and also just water. It then looked for oxygen, nitrogen, Carbon dioxide,
methane and hydrogen that might have been products of life, but only because those
gases are associated with how life on earth is. And, it produced something rather odd,
and did it from both identical instruments on each of the two landers. Whenever the nutrient
solution went into the soil, oxygen disappeared and carbon dioxide appeared. Life does that,
we do it in our respiration. But that alone on Mars is tricky because oxygen
is extremely reactive with or without life. Not quite a detection, but would support one.
The third experiment performed was the most enigmatic, and still haunts the field of
astrobiology to this day because if it’s results were accurate, then astrobiology
goes from a speculative science with only earth life as a reference to an actual science with
something to study and due to the circumstances of the experiment that if it had just done a few
other things, and those had gone equally well, we’d very likely be studying Martian microbial
life right now in the laboratory here on earth. This was known as the labeled release experiment.
Out of the four life sensing experiments, this one was the one that held the most promise. What
happened here was that soil samples were exposed to a dilute solution of nutrients again, but not
just any nutrients. These were the seven molecules produced by the miller-urey experiments, which
showed that when you subject chemicals expected to be present on earth earth, in what was thought to
be an atmosphere consistent with early earth and introduce an energy source, out come sugars, amino
acids and the chemicals life uses proving that they were present very early in earth’s history.
On viking, these were tagged with carbon 14, so that if any carbon based gases like carbon
dioxide appeared, they would incorporate the carbon 14 supporting that whatever produced
that did it by metabolizing the nutrients. Both viking probes returned a positive,
they detected metabolism in the Martian soil and the incorporating of the carbon 14. Both Viking
landers actually did this somewhat differently, one took a sample from soil exposed to sunlight,
and the other took a sample from beneath a rock, and both resulted in the same thing.
Even more interesting were the control experiments. Samples that were heated, basically
baked at 160 degrees celsius, 320 fahrenheit for 3 hours, stopped producing the gases when
the nutrients were injected as though whatever was metabolizing the the soil was killed by the heat.
Samples similarly baked at 50 celsius for the same amount of time, did show production of
radioactive gas but at a much lower rate. Yet again, a sample not subjected to high heat,
but warmer than mars usually gets at 10 degrees celsius was stored for several months. Again,
injecting the nutrients resulted in a decreased metabolism, again what you might expect for life.
Whatever happened there, was behaving very similarly to microbial life on earth.
But there was a problem. With earth life, if you do the same experiment you get something a bit
different. Yes, you get the initial result of the Viking experiments, but with the experiments on
Mars if you went back and injected nutrients again into the soil samples after the first
wave of experiments, nothing happened. They tried second and third nutrient injections to no avail.
On earth, this results in the dormant bacteria coming back and consuming the
nutrients again. Whatever metabolized the nutrients in the Martian soil,
was done for one way or another after the initial test.
This called the results into question, but here it gets complicated as subsequent research has
yielded some clues. Researchers at JPL were able to determine how that, in the extremely
cold conditions of the martian surface, in a C02 atmosphere as Mars has, and UV from the sun,
of which Mars has little protection, can cause atmospheric CO2 to react in soil and produce
highly reactive oxides that might react with organic molecules such as the nutrients in the
experiment to produce carbon dioxide, including incorporating the carbon 14. This might account
for the results, and also might account for the second and third tries where nothing was detected
because the chemical reaction that caused the initial result no longer had fuel,
so to speak. Also the oxidizer here was a super oxidizer that often gets destroyed when heated,
which could have mimicked the sterilization experiment at high heat.
But it didn’t end there. More recent work has shown that it may not be that simple.
Subsequently, about 20 years ago, it was speculated that the delays
in the reactions from the data might have pointed to a biological origin on their own,
related to circadian rhythms, which is noted in some kinds of cyanobacteria on earth.
In 2012, Gil Levin, the designer of the experiment, and Dr. Patricia Ann Straat,
one of the principle scientists on the original experiment published new results
that again seemed to support a microbial origin for the labeled release experiment.
For those interested, I interviewed Dr. Straat on the subject on Event Horizon only a few months
before she sadly passed away, link below. This was one of the more important interviews I’ve
ever done. One of my aims with Event Horizon is to document past unresolved mysteries in
science while the scientists involved are still around to make their case in a current context,
and in this case Dr. Straat may well be remembered as one of the co-discoverers of alien life.
In 2008 a further discovery was made. The Phoenix lander detected the presence of
the chemical perchlorate in the soil of Mars. This has often been mischaracterized as a show
stopper for life on Mars, but it actually is not. Perchlorate isn’t a very good oxidizer of
organics until you heat it significantly, but if you do that as one of the experiments did,
then it destroys organics. That was one of the points of the original argument
against the results of the Viking life search experiments, that almost no organics were found,
but under these conditions the organics would have been destroyed. It’s been estimated that
before heating, the samples could have had significant amounts of organic chemicals
and indeed Mars has since been shown to have organics in its soil. This moved the
Viking life detections from probably not, to the current thinking of inconclusive.
The organics that were found were weird, they were chloromethane and dicholormethane, which
are chlorine compounds. Because of this they were dismissed as contaminants from earthly cleaning
fluids. This was due in part to the isotope ratios of the compounds matching earth, the problem was
that we didn't yet know what ratios Mars has. We do now as of 2021, and they are the same as earth.
So this very well may have been an error early on because those two chemicals have also since
been proven to result from reactions of perchlorate to very dry desert soils on
earth similar to the Martian soil. Again, it moved from case closed to inconclusive.
The final experiment also produced an interesting result. It was known as the pyrolitic release
experiment. Again it used carbon 14, but in a different way, to see if carbon could be fixed
like plants on earth do, essentially looking for photosynthesis. The sterilized control sample
showed no evidence of this, but the experiment yielded a positive. This finding was dismissed
because of the results of the GCMS experiment, but with that in question now, this detection too
comes back on the table as a possible detection of biology on Mars. It’s also been pointed out that
the GCMS experiment might have also produced a null result because the amount of organisms
needed to produce the results of the Labeled Release Experiment were too low for it to detect.
At the same time however other findings regarding the chemistry of Mars have opened up other avenues
that may partly explain the Viking detections chemically, without the need to invoke biology,
but these are ongoing. Unfortunately the direct life detection experiments, and
the questions that surrounded them, caused NASA to essentially get out of the direct detection
business and focus on a follow the water plan, to try to understand if Mars could have hosted
life through a roundabout means because direct detections seemed to only lead to ambiguity,
though this more recently being rethought due advances in technology since 1976.
So the results of the Viking life finder experiments are no longer seen as unlikely, but
inconclusive over all, and it’s not just one of the experiments that exhibited intriguing results.
Three of the four did. At the same time though, Mars is a very harsh place, and there is some
reason to doubt that life could exist in its very uppermost layers of soil. But life is resilient.
That said, if there is life on Mars we should really try to find out before sending anyone
there. If contamination were possible though, Mars would have dropped it on earth long ago in
a meteorite, and it’s highly unlikely that a Martian organism could infect a human,
or for that matter any life on earth. But there is another question here, if microbial life is indeed
found on Mars conclusively, and shown to be of truly alien origin not related to life on Earth,
should we still explore Mars, or should we set it aside as a nature preserve?
Thanks for listening! I am futurist and science fiction author John Michael Godier
currently eyeing Mars suspiciously. There is actually another somewhat odd point about Mars,
it’s rusted and it’s not entirely clear how that happened on a global scale,
but iron meteorites on the surface found by the rovers are not rusted, so whatever it was,
it’s apparently gone or very slow acting. Oddly the moon also has rust, and it’s not entirely
clear how or why but it is close to an oxygen planet and once was far closer. But like Mars,
Earth too rusted early in its history, and it was photosynthetic life producing oxygen that did it.
Mysteries indeed and be sure to check out my books at your favorite online book retailer
and subscribe to my channels for regular, in-depth explorations into the interesting,
weird and unknown aspects of this amazing universe in which we live.