Science Writing

Life on Mars

In 1976 two landers touched down on the surface of the red planet, Viking 1 and Viking 2. They were sent their by NASA almost a year earlier with one purpose: to search for life.

To do this, they both carried the same four instruments, designed in the same way with the same parameters.

Three of these four returned negative or null results, the fourth came back positive.

The story of the Labelled Release experiment performed by Viking 1 and 2 is not well known, but the results that it returned are still being debated today. Surely, if life were found on Mars like the LR experiment said, the whole world would know about it. The foundations of every country, society, religion would have been shaken to the core.

And yet, none of this happened, because as soon as the result came back positive, people searched for a way to explain it away as anything but life.

The LR experiment was simple; the lander collected a sample of Martian dirt and injected it with an aqueous mix of nutrients that were previously tagged with radioactive Carbon14. The idea being that any microbial lifeforms in the dirt would metabolise the nutrient mix and cause an increase in the detectable radioactive C14 released.

And this is exactly what happened. To the shock of the team waiting for results on Earth, a steady stream of carbon was released from the dirt, signaling that life did indeed exist on the surface of Mars.

Patricia Ann Straat, one of the Viking LR team members, recently spoke to Scientific America about the moment that the positive results came in.

‘Oh my God, it’s positive.’

Patricia describes the moment as ‘quite a thrill’ but when asked if they thought they had found life the response is less than certain.

‘Oh no. We weren’t convinced either.’

This is where the second part of the LR experiment came into play. The control stage. This involved heating the soil sample to around 160 degrees, thus killing any microbial life within and sterilsing it. The thinking being that if it were a chemical reaction and not metabolism, the C14 would rise, regardless of the heating of the sample.

But it didn’t.

The control was negative. As Patricia Straat states, ‘That’s when the controversy really started.’

The team behind the LR experiment were stringent with their testing. They performed several runs with the 160 degree control and also runs at 50 degrees and a test run after three months at 10-26 degrees (but exposed to the Martian atmosphere.

Everything pointed to a positive result. Biological agents under 50 degrees of heat on Mars would be unlikely to survive as the average surface temperature of Mars is roughly -50 degrees, however, if the LR positive was a chemical reaction 50 degrees of heating would not have affected the result. The result of the 50 degree test was negative, pointing to biological metabolism.

And yet, to this day, there are doubts about the result.

For almost fifty years the lead designer of the LR experiment, Gilbert Levin, has championed the positive life response on Mars despite skepticism from the general scientific community. Throughout the half-century since the LR experiment, countless people have come forward with non-biological theories, but none have satisfactorily debunked the LR results by perfectly replicating or explaining them.

In a 2016 study performed by Straat and Levin, published in the Astrobiology Journal, they go to great lengths to give the leading non-biological theories their due, however the conclusion remains the same.

There has yet to be comprehensive chemical response to explain away the positive life result from the LR experiment.

It seems then it’s appropriate to ask why the scientific community are hesitant to accept these results?

Yes, it is the job of scientists to question and test results again and again, as they have done here for almost fifty years. But after such a great length of time and with no non-biological answer, why is there still this hesitation?

In recent years, thanks to other Mars missions such as Curiosity, Opportunity, and Phoenix, it has been revealed that water exists on Mars and underneath it. There is a subsystem of lakes beneath the surface and water, albeit not in it’s liquid form, appears abundant. Add to that the strange, as yet unexplained, fluctuations of methane in the Martian atmosphere and more questions are raised.

Methane is a well-known biological waste product and in 2018 NASA announced that there was a cyclical variation in methane throughout the Martian atmopshere.

Is there an aspect of arrogance in our reluctance to give life on Mars the stamp of approval? Are we, as a species, inclined to err on the side of hubris when faced with a revelation that would challenge our place in the Universe?

Or is this reluctance an aspect of scientific rigor? An appropriate pause to allow for challenges to the results until all candidates are accounted for.

It is hard to say. Complex organic molecules have not been found on the surface of Mars; this is often held up as evidence that life cannot exist there. But humanity has only ever known one type of life. We have a sample size of one planet to go from and any scientist will tell you that is not a strong foundation to lean assumptions on.

Do we need to expand our criteria for life? Mars, and other planets and moons, have vastly different atmospheres and conditions than Earth. Is it arrogant to think that life, if it evolved in these places, would have the exact same basis as life on Earth does?

The LR results are controversial, but they don’t have to be.

We can accept them; yes, life exists on Mars, and the world doesn’t shatter, humanity won’t be brought to its knees.

Yes, life exists on Mars but it is a different variation of life.

Not better, or worse, merely different.

Further Reading:

The Case for Extant Life on Mars and Its Possible Detection by the Viking Labeled Release Experiment (

Looking for Life on Mars: Viking Experiment Team Member Reflects on Divisive Findings – Scientific American

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