Apologies for the clickbait title but the short answer is no.
However, this is something that came up a few times during our
live Reddit Q & A session yesterday in the run up to Perseverance’s landing.
I only had time to go into it briefly then so I thought I’d expand here for
anyone who is interested in the details.
The real interesting question is: ‘Do some NASA scientists
believe they found evidence of life on Mars in the 70’s and still think they’re
being undeservedly ignored/silenced by the rest of the scientific community?’
Because the answer to that is a surprising yes.
Planning for the first landed missions to Mars started
almost 70 years ago in the 1950’s. Back then it was thought that the surface of
Mars was a much more benign environment than we know it to be today. Early
observations of the planet seemed to suggest that there was seasonal vegetative
cover and serious scientists (including Carl Sagan) postulated the idea of large martian animals
roaming a landscape similar to Earth's in serious journals.
It wasn’t until the Mariner Mars orbiter missions in the mid-late ‘60s that we
got clear images back of the martian surface. While these showed it to be a more
hostile, empty desert environment with no signs of animal or plant life, nor
liquid water at the surface, the low resolution meant it did not preclude the existence of even macrofauna. Because of this, it was a real worry that microorganisms
hitching a ride on Mars landers could invade the surface, outcompeting and
leading to the extinction of any putative microscopic Martians, and wiping out
our ability to ever know that life had ever existed on another planet.
This led to the Viking mission having the most intense
planetary protection effort and the production of the cleanest, most sterile
spacecraft, Viking 1 & 2, that have ever been launched. The expectation that
we would find habitable surface conditions and martian microbes also led to one
of the most interesting experiments ever carried out on another planet.
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| Viking lander, Carl Sagan for scale (credit: NASA) |
The Labelled Release Experiments carried by both Viking landers were devised by Gilbert Leven and Patricia Straat. These experiments involved scooping up a sample of martian surface soil, ‘feeding’ it a nutrient broth labelled with radioactive isotopes and providing a little heat and water, then measuring any radioactive gas produced as the broth was ‘eaten’ by respiring martian microbes. On Mars, these experiments ‘worked perfectly’. When ‘fed’ the soil produced the radioactive gas exactly as would be expected if martian microbes were present. If the soil was first heat sterilised to kill any microbes present then less gas was produced as would be expected. The designers of the experiment and many others saw this as a huge success and clear evidence of life on Mars and published papers to that effect.
The first evidence that not all was as it seemed came
quickly. The Viking landers were also equipped with instruments to analyse the martian
soil to look for organic matter – which would be direct evidence of either the
microbes themselves or their normal food source. Despite multiple attempts, no
organic molecules were detected other than simple chlorinated molecules
accompanied by large releases of carbon monoxide and carbon dioxide. This was problematic,
a lack of organic matter in the soil meant no food for martian microbes to live
on (when they weren’t being fed by us). This meant that very soon, most
scientists preferred the hypothesis that the results of the Labelled Release
Experiment could be caused by some strongly oxidising mineral, present in the
martian soil, acting like a bleach to break down the nutrient broth, instead of
the presence of martian microbes. At best the results were ambiguous. Levin and
Straat disagreed, and have continued publishing support for their ‘life
detection’ up to the present (Patricia Straat died in October 2020).
The mystery of the strong oxidant persisted for 40 years
until the Phoenix lander detected perchlorate in the martian soil. Perchlorates
and other oxychlorines have since been detected all over Mars by subsequent
missions. Perchlorates are strongly oxidising chlorine containing salts. It is
their presence that is believed to have caused the gas release measured in the
Labelled Release Experiment as they oxidised the organic carbon ‘food’ in the
nutrient broth on heating, mimicking biological activity. The presence of
perchlorates also explains the lack of detection of organic matter by Viking’s
thermal decomposition GCMS experiments. On heating in the sample oven, the
perchlorates break down, releasing large amounts of oxygen and chlorine. This
reacts with any organic matter present, causing it to combust and essentially
burn away. This neatly explains the carbon dioxide and carbon monoxide, and the
simple chlorinated molecules which were detected by Viking 1 & 2 and, more
recently (since 2012), the Curiosity Rover.
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| Phoenix (credit: NASA) |
So no, we haven’t yet detected evidence of life on Mars, the results of the Labelled Release Experiment can be more simply explained abiotically.
With everything we now know about the hostility of the
martian surface we really don’t expect to find anything living there. The deep subsurface,
sheltered from the harsh effects of UV radiation, solar and galactic rays, oxidising
chemicals, extreme temperature fluctuations and aridity, is another matter
entirely though. I would be very surprised if we never find evidence of at
least extinct life on Mars, and am hopeful we will one day find weird microbes
living deep beneath its surface.
Being the first step of eventual Mars Sample Return, planned
for completion sometime in the 2030’s, the successful landing of NASA’s Perseverance
rover yesterday will hopefully bring us one step closer to finally answering
the question of whether there was ever life on Mars.
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| The first image sent back by Perseverance last night, minutes after landing (credit: NASA) |
One final point for anyone who is not convinced about the lack of some great NASA conspiracy covering up life on Mars, and which also covers things like aliens visiting us, Oumuamua being an alien spaceship and flat Earth battshittery: If you saw the live coverage of the landing last night, or follow the Twitter accounts of the hundreds of NASA employees and thousands of scientists actively involved in these missions, you’ll see just how excited everyone gets and just how much they want to share EVERYTHING with the whole world. You really think these people could keep come massive discovery like that quiet? That’s just stupid...
