We may have killed the only life we ​​found on Mars

I was recently invited to speak at a Symposium organized by the Royal Palace Foundation in Amsterdam, which twice a year brings experts to discuss some important topics such as the COVID pandemic or the future of work. This summer’s meeting was about the search for extraterrestrial life. While I focused on researching our solar system, Sarah Seager from the Massachusetts Institute of Technology presented her ideas on how to search for life on planets orbiting other stars.

During our conversations and the discussions that followed, I dropped a suggestion that some people would surely find provocative: that we already done Life existed on Mars more than 50 years ago – but we accidentally killed it.

Viking probe experiments

In the mid-1970s, NASA sent two Viking rovers to the surface of Mars, equipped with instruments The only life detection experiments conducted on another planet. The results of those tests were very baffling at the time and remain so today. While some—notably the labeled release experiment (which tested microbial metabolism) and the pyrolysis experiments (which tested organic synthesis)—were initially positive for life, the gas exchange experiment was not.

The Viking lander also included an organic compound detector. It saw trace amounts of chlorinated organic matter, which was interpreted at the time as the result of pollution from the ground. This prompted Vikings project scientist Gerald Sovine to utter his famous words, “No bodies, no lives.” In other words, Martian life could not exist without organic compounds. So Sovine concluded, as did most other scholars of the time, that the Viking Project was negative about the existence of life, or at best inconclusive.

In the half century since then, the picture has changed a lot. Eight landers and a rover have explored the surface of Mars in more detail. Thanks 2008 Phoenix Lander, and to confirm later by curiousity And perseverance Rovers, we know that In fact, the original organic compounds are found on Mars. However, it is in a chlorinated form – not what Viking Age scientists expected – and we don’t know if it derives from biological processes or from some Abiotic chemical reactions It has nothing to do with life. However, one might wonder how Soffen would react today: would he still say categorically that Viking’s results were negative?

death by water

At the time of the landings, scientists had little understanding of the Martian environment. Since Earth is a watery planet, it seemed plausible that adding water might coax life into manifesting itself in Mars’ extremely dry environment. In hindsight, it’s possible that this approach was a very good thing. What I and other researchers have learned in extremely arid places on Earth, such as the Atacama Desert in Chile, is that there is a gradual advance in life forms as the habitat becomes drier.

At the end of this progression you find Microbes that live entirely inside salt rocks. These tough organisms benefit from a process we call hygroscopicity, by which certain salts attract water directly from the relative humidity of the air. (This is the same process that makes table salt clump when you leave it exposed to the air.) For this reason, the microbes that live inside the salt rocks of the Atacama don’t need any rain at all—just a certain amount of moisture in the atmosphere.

Now let’s ask what would happen if you poured water on these drought-adapted microbes. Could that confuse them? Technically, we could say we were over-moisturizing it, but in simple terms, it would be like over-moistening it. It would be as if an alien spaceship finds you wandering half dead in the desert, and your would-be saviors decide, “Humans need water. Let’s put human in the middle of the ocean to save him!” That wouldn’t work either.

Many of the Vikings’ experiments involved applying water to soil samples, which may explain the puzzling results. The putative Martian microbes collected for the classified launch experiments probably couldn’t handle that amount of water and died after a while. Most of the runs for the pyrolysis experiment were done under dry conditions, in contrast to the other experiments. The first run was positive for life when compared to a control run performed later, which was designed so that no biology could be involved. Interestingly, the only run performed under wet conditions had a lower signal than the controller.

Following this line of thought, we must ask whether the Martian soils tested by the Vikings did indeed contain hygroscopic salts, and whether the relative humidity at those locations was sufficiently high. The Vikings landed in the equatorial region of Mars where the salt content in the soil is rather low. But there is a lot of hydrogen peroxide and perchlorate in the soil, and both are very hygroscopic compounds. Also, the Vikings noticed that there was haze on Mars – which means 100% humidity. In principle, the relative humidity was high enough in the morning and evening hours for microbes to absorb moisture.

Hope of hydrogen peroxide

More than 15 years ago, my colleague Job and I were a hotcooper It raised the level of scientific speculation on this subject By taking a different perspective on Viking’s puzzling results. We suggested that microbial life on Mars might contain hydrogen peroxide in their cells – an evolutionary adaptation that would allow them to draw water directly from the atmosphere. The mixture would have other advantages, too, such as keeping water liquid at freezing temperatures on Mars, and preventing the formation of ice crystals that would rupture cells.

While hydrogen peroxide is used in a high concentration for cleaning and sterilization, a lot The microbes in your mouth, eg streptococcus; And lactobacillus, Hydrogen peroxide is produced naturally, along with others, such as Neisseria sicca and Haemophilus segnis, that you are using. The bombardier beetle sprays a 25% hydrogen peroxide solution on anything that bothers it. My point is that hydrogen peroxide is not incompatible with life.

If we hypothesize that indigenous Martian life may have adapted to its environment by incorporating hydrogen peroxide into its cells, this could explain the Vikings’ findings. The instrument used to detect organic compounds (called a gas chromatograph-mass spectrometer) heated soil samples prior to analysis. If Martian cells contained hydrogen peroxide, that would have killed them. What’s more, it would have caused the hydrogen peroxide to react with any organic molecules in the vicinity to create large amounts of carbon dioxide – which is exactly what the instrument detected.

New mission to Mars

Like I said before, we need a new mission to Mars Primarily dedicated to the discovery of life To test this hypothesis and others. It should explore possible habitats on Mars such as the Southern Highlands, where life could persist in salt rocks near the surface. We might even be able to get to these rocks without digging—a huge advantage in terms of engineering complexity and cost. I can’t wait for you to start a mission like this.