Lately, I used to be invited to talk at a symposium organized by the Amsterdam Royal Palace Basis, who, twice a 12 months, brings in consultants to debate some huge matter just like the COVID pandemic or the way forward for work. This summer time’s assembly was concerning the seek for extraterrestrial life. Whereas I centered on the search in our personal Photo voltaic System, Sara Seager of MIT introduced her concepts on how one can search for life on planets circling different stars.
Throughout our talks and the discussions that adopted, I dropped a suggestion that some folks absolutely will discover provocative: that we already did discover life on Mars practically 50 years in the past—however that we inadvertently killed it.
The Viking Lander Experiments
Within the mid-Seventies, NASA despatched two Viking landers to the floor of Mars geared up with devices that performed the one life detection experiments ever performed on one other planet. The outcomes of these checks had been very complicated on the time and stay so at present. Whereas a few of them—significantly the labelled launch experiment (which examined for microbial metabolism) and the pyrolytic launch experiments (which examined for natural synthesis)—had been initially optimistic for all times, the fuel change experiment was not.
The Viking landers additionally included an instrument to detect natural compounds. It noticed hint quantities of chlorinated organics, which had been interpreted on the time to be the results of contamination from Earth. This led Viking venture scientist Gerald Soffen to utter his well-known phrases, “No our bodies, no life.” In different phrases, there couldn’t be Martian life with out natural compounds. So Soffen concluded, as did most different scientists on the time, that the Viking venture was damaging as to the presence of life, or at greatest inconclusive.
Within the half century since, the image has modified loads. Eight extra landers and rovers have explored the Martian floor in better element. Because of the 2008 Phoenix lander, and to later affirmation by the Curiosity and Perseverance rovers, we all know that indigenous natural compounds do, in actual fact, exist on Mars. They’re in a chlorinated type, nonetheless—not what the Viking-era scientists anticipated—and we don’t know whether or not they derive from organic processes or from some abiotic chemical reactions that don’t have anything to do with life. Nonetheless, one may marvel how Soffen would react at present: Would he nonetheless say categorically that the Viking outcomes had been damaging?
Dying by Water
On the time of these landings, scientists had little or no understanding of the Martian setting. Since Earth is a water planet, it appeared affordable that including water may coax life to point out itself within the extraordinarily dry Martian setting. In hindsight, it’s attainable that strategy was an excessive amount of of a great factor. What I and different researchers have realized in extraordinarily dry locations on Earth, resembling Chile’s Atacama Desert, is that there’s a gradual development of life kinds because the habitat will get extra arid.
On the very finish of that development, you discover microbes that stay solely inside salt rocks. These hardy organisms reap the benefits of a course of we name hygroscopicity, by which sure salts entice water straight from the relative humidity of the air. (This is similar course of that makes desk salt clumpy whenever you depart it uncovered to air.) For that purpose, the microbes residing inside salt rocks within the Atacama don’t want any rain in any respect—simply a specific amount of moisture within the environment.
Now let’s ask what would occur if you happen to poured water over these dry-adapted microbes. May that overwhelm them? In technical phrases, we might say that we had been hyperhydrating them, however in easy phrases, it will be extra like drowning them. It might be as if an alien spaceship had been to seek out you wandering half-dead within the desert, and your would-be saviors determine, “People want water. Let’s put the human in the course of the ocean to reserve it!” That wouldn’t work both.
Lots of the Viking experiments concerned making use of water to the soil samples, which can clarify the puzzling outcomes. Maybe the putative Martian microbes collected for the labelled launch experiments couldn’t take care of that quantity of water and died off after some time. Many of the runs for the pyrolytic launch experiment had been performed underneath dry situations, opposite to the opposite experiments. The primary run was optimistic for all times when in comparison with a management run performed later, which was designed in order that no biology might have been concerned. Apparently, the one run performed underneath moist situations had much less of a sign than the management.
Following this line of thought, we must always ask whether or not the Martian soil examined by Viking did in actual fact include hygroscopic salts, and whether or not the relative humidity at these websites is excessive sufficient. The Vikings touched down within the equatorial area of Mars the place the salt content material of the soil is somewhat low. However there are plenty of hydrogen peroxide and perchlorates within the soil, and each of these compounds are very hygroscopic. Additionally, Viking did observe fog on Mars—which suggests one hundred pc humidity. In precept, relative humidities would have been excessive sufficient within the morning and night hours for microbes to suck up the moisture.
Hope from Hydrogen Peroxide
Greater than 15 years in the past, my colleague Joop Houtkooper and I upped the extent of scientific hypothesis on this matter by taking a unique perspective on the puzzling Viking outcomes. We recommended that microbial life on Mars may need hydrogen peroxide of their cells—an evolutionary adaptation that will permit them to attract water straight from the environment. The combination would produce other benefits, too, resembling conserving water liquid at freezing Martian temperatures, stopping the formation of ice crystals that will rupture the cells.
Whereas at a excessive sufficient focus hydrogen peroxide is used for cleansing and sterilization, many microbes in your mouth, like Streptococcus and Lactobacillus, produce hydrogen peroxide naturally, alongside others, like Neisseria sicca and Haemophilus segnis, that use it. The bombardier beetle sprays a 25 p.c hydrogen peroxide resolution at something that bothers it. My level is that hydrogen peroxide shouldn’t be incompatible with life.
If we assume that indigenous Martian life may need tailored to its setting by incorporating hydrogen peroxide into its cells, this might clarify the Viking outcomes. The instrument used for detecting natural compounds (referred to as a fuel chromatograph-mass spectrometer) heated up soil samples previous to evaluation. If the Martian cells contained hydrogen peroxide, that will have killed them. Furthermore, it will have precipitated the hydrogen peroxide to react with any natural molecules within the neighborhood to type giant quantities of carbon dioxide—which is precisely what the instrument detected.
A New Mission to Mars
As I’ve argued earlier than, we want a brand new mission to Mars devoted primarily to life detection to check this speculation and others. It ought to discover potential habitats on Mars just like the Southern Highlands, the place life might persist in salt rocks near the floor. We’d even be capable to entry these rocks with out drilling—an enormous benefit by way of engineering complication and price. I can not anticipate such a mission to get underneath method.
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