When the Viking 1 and 2 landers analyzed the Martian sands for microbial life again within the late Nineteen Seventies and early Nineteen Eighties, the outcomes have been … inconclusive. A few of the experiments got here again optimistic for microorganisms surviving the cruel situations – as we speak, not simply within the historic previous – however others didn’t. It was perplexing then and nonetheless is as we speak. Most scientists have since concluded that the optimistic outcomes have been inaccurate, as a result of neither lander discovered any ample natural materials within the soil. How may there be microbes with no organics, the constructing blocks of life? However perhaps there’s one other chance. What if there have been microbes, however the soil exams on the rovers by accident destroyed them within the course of?
That idea has been round for some time. Astrobiologist Dirk Schulze-Makuch revisited this intriguing concept in a new post for Huge Assume on June 27, 2023.
4 experiments to search for life on Mars
The Viking landers carried out 4 primary experiments. The landers performed them on samples of soil that they dug from the bottom. Every lander scooped samples into their onboard laboratory. Though not as refined as labs again on Earth, they have been thought of fairly able to detecting residing microbes, in the event that they existed.
The Labeled Release Experiment appeared for indicators of metabolism, chemical reactions in organisms that maintain life processes. That features the conversion of vitality in meals to vitality accessible to run mobile processes; the conversion of meals to constructing blocks for proteins, lipids, nucleic acids and a few carbohydrates; and the elimination of metabolic wastes.
The Pyrolytic Release Experiment appeared for proof of organic synthesis. That’s the intentional development of natural compounds.
These first two experiments appeared to yield optimistic outcomes. However the third experiment, the Gas Exchange Experiment, didn’t. First, it added small quantities of water to the samples. This was an try and see if any dormant microbes can be revived by moisture, since Mars is now so bone dry. It additionally added a “hen soup” broth containing 19 amino acids, nutritional vitamins, different natural compounds and some inorganic salts. Would any microbes eat this scrumptious meal?
The place are the organics?
Scientists have been excited on the preliminary optimistic outcomes from the Labeled Launch Experiment and Pyrolytic Launch Experiment. There was one massive drawback, nevertheless. The Vikings additionally looked for organics within the soil with their fourth experiment, the Gas Chromatograph-Mass Spectrometer instrument. With out organics, there may very well be no life. All they discovered have been tiny traces of chlorinated organics. These are natural compounds containing a minimum of one covalently bonded atom of chlorine. Since solely these and no different organics have been discovered, the mission scientists concluded that they have been most definitely earthly contaminants on the landers. They weren’t merchandise of life and possibly didn’t even originate on Mars.
The dearth of different organics was a blow to the potential of life inhabiting the Martian sands. As Schulze-Makuch wrote:
The Viking landers additionally included an instrument to detect natural compounds. It noticed hint quantities of chlorinated organics, which have 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 destructive as to the presence of life, or at finest inconclusive.
Organics on Mars in any case
Because it turned out a long time later, there are organics on Mars. They usually’re native to the planet, not contaminants that spacecraft from Earth introduced there. The Curiosity and Perseverance rovers have now confirmed them past any doubt. Beforehand, the Phoenix Mars Lander was the subsequent mission after Viking to seek out organics once more.
Simply as Viking had discovered, the organics are chlorinated. It’s additionally now identified that the Martian soil comprises perchlorates, which may destroy natural molecules. This may also assist clarify the very low abundance of organics the place the Viking landers sampled. A lot of the organics discovered extra lately have been preserved in rocks.
Simply add water
One of many key targets within the Viking experiments was so as to add small quantities of water to the soil samples. The concept was that microbes within the soil may be dormant as a result of extraordinarily dry and freezing situations. Including water would possibly rejuvenate them to change into energetic once more. Schulze-Makuch surmised, as have others, that this may occasionally have been an excessive amount of of an excellent factor. As a substitute of simply offering moisture for the microbes to soak up or drink, it drowned them. Any Martian microbes can be well-adapted by now to the hostile and very dry situations. Schulze-Makuch wrote:
Now let’s ask what would occur when you poured water over these dry-adapted microbes. Would possibly that overwhelm them? In technical phrases, we might say that we have been hyperhydrating them, however in easy phrases, it will be extra like drowning them. It might be as if an alien spaceship have 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 put it aside!’ That wouldn’t work both.
Hygroscopic life on Mars?
Maybe Martian microbes may be like ones on Earth within the Atacama Desert in Chile that reside solely on salts, no liquid water, like rain. They use a course of known as hygroscopicity, the place some salts in soil take up water immediately from the relative humidity of the air.
As Schulze-Makuch famous, the soil on the Viking touchdown websites was low in salts. Nonetheless, it did include perchlorates and hydrogen peroxide. Each of these are extremely hygroscopic by nature. Additionally, the Viking orbiters noticed fog in valleys from orbit. Meaning the relative humidity within the mornings and evenings ought to have been excessive sufficient for the moisture within the fog to be accessible to microorganisms.
Hydrogen peroxide: One other chance for all times on Mars
The Viking experiment outcomes have been certainly irritating for the scientists. A few of the outcomes appeared to point life whereas others didn’t. Then there was the dearth of ample organics. Most scientists now assume that the outcomes could be defined by non-biological chemical reactions. However there’s additionally one other chance.
Schulze-Makuch and his colleague Joop Houtkooper on the College of Giessen in Germany had beforehand proposed a novel organic rationalization for the Viking outcomes. What if Martian microbes had hydrogen peroxide of their cells? Hydrogen peroxide could be lethal in massive quantities, however there are literally microbes on Earth that use it and produce it. These embody Neisseria sicca, Haemophilus segnis, Streptococcus and Lactobacillus.
On Mars, theoretically, microbes with hydrogen peroxide of their cells may siphon tiny quantities of water immediately from the ambiance. It might additionally assist to maintain the water from freezing once more contained in the microbes and damaging their cells.
Schulze-Makuch makes the case that such hydrogen peroxide microorganisms may clarify the puzzling Viking outcomes. The Fuel Chromatograph-Mass Spectrometer, by design, heated the soil samples earlier than analyzing them. The scientists needed to see if any organic compounds can be launched within the course of. However in hindsight, this may occasionally have really destroyed any microbes current. If the microbes did occur to include hydrogen peroxide, the extreme warmth would possible have killed them. So, on this situation, warmth would have killed off the microbes as a substitute of water. Furthermore, the hydrogen peroxide would have reacted with the natural compounds to provide carbon dioxide. And, perhaps it was a coincidence, however that’s precisely what the Fuel Chromatograph-Mass Spectrometer detected.
Gilbert Levin
On a associated be aware, Gilbert Levin, who was the principal investigator for the Labeled Launch Experiment for each Viking landers, maintained that we did find life on Mars. He outlined his stance in an opinion piece in Scientific American on October 10, 2019. He handed away in 2021 on the age of 97.
We might by no means know for absolute certainty that the Viking landers did discover life – or didn’t – however the perplexing outcomes will help scientists higher plan future life-detection missions. There may be nonetheless a lot to be taught, particularly in hindsight, as scientists like Schulze-Makuch remind us.
Backside line: Did the Viking landers from just a few a long time in the past discover microbial life on Mars in any case? Astrobiologist Dirk Schulze-Makuch makes the case in Huge Assume.
Related: Did the Viking landers find life on Mars in 1976?
