It's critical to detect life on Mars before humans set foot on the red planet
Bob McDonald's blog: how we can avoid accidental microbiological 'wars of the worlds'
After celebrating another successful landing on Mars, we're inching closer to answering the big question: Is there — or was there ever — life on our planetary neighbour? That question needs to be answered before humans go there because of the risk of contamination in both directions.
The Perseverance rover landed at the mouth of a river delta in a crater that used to be a lake. The rover carries a suite of instruments that will examine the chemistry and geology of the rocks looking for signs that life could have existed there in the distant past. But it does not carry a biology experiment to directly look for life that might exist there now.
Mars has always intrigued us with the possibility of life. It is the most Earth-like planet with mountains, valleys, an atmosphere and ice at both poles. Early astronomers, such as Percival Lowell, believed they saw intersecting lines crossing the surface of the planet, which were interpreted as canals, suggesting an intelligent civilization building those artificial waterways.
The idea of an advanced civilization on Mars inspired H.G. Wells' story, War of The Worlds, (and subsequent movies), where technologically superior Martians invade Earth with invincible machines that destroy everything in their path. In the end (spoiler alert) the malevolent Martians are not defeated by humanity, but are instead brought down by the simplest forms of life, the viruses that cause the common cold. The aliens had no resistance to infection by Earthly organisms.
If there is life on Mars today, it is most likely microscopic, since we haven't spotted any artificial canals, or little green men passing by our cameras. If we send people there, and Martian microbes still exist in that environment, a war of the worlds scenario could play out in reverse as we pick up Martian germs. Or worse, we could just swap microbes and simultaneously infect each other. That's why it is important to answer the question of life on Mars before humans set foot there.
Of all the missions to the Red Planet, only one carried biology experiments specifically designed to search for life. The twin Viking landers touched down on opposite sides of Mars in 1976 and carried out experiments in which soil samples were fed liquid nutrients and incubated. Instruments looked for gasses such as oxygen that would be given off by biological activity metabolizing those nutrients.
Those experiments detected traces of gases, which had the biologists very excited. But another experiment on the same mission searched for organic molecules in the soil and failed to find any. No organics means no life, so the conclusion was that the gasses released in the biology experiments were not a sign of life, but the result of ordinary non-biological chemical reactions.
Since then, more sensitive instruments carried aboard the Curiosity rover and other landers have detected organics in Martian soil, along with methane in the atmosphere which can be produced by biological activity. This, along with abundant evidence that Mars was once a wet world with lakes and rivers (but no canals) in the distant past, is tantalizing evidence. But it's not conclusive because we now know these products can also be produced by non-biological chemical and geological processes.
The lead scientist on one of those Viking experiments 45 years ago, Gilbert Levin, believes the experiments did find life and suggested a similar, improved version could be carried on lands like Perseverance, but that hasn't happened.
One of the tasks of Perseverance is to select rocks that will be sealed and cached to be picked up by later missions and returned to Earth where they will be scrutinized for life. But it will be a decade or so before a Mars sample-return mission will be launched.
In the meantime, Elon Musk of Space-X is testing a new rocket that he hopes will bring people to Mars as soon as possible. If the question of life is not answered by then, the Martian explorers run the risk of being infected by alien organisms, while the entire ecosystem of another planet could be threatened by invaders from Earth.
Finding life on another planet is more than just answering the fundamental question of whether we are alone in the universe, it could be a matter of survival — for us and for them.