Nearly half a century after NASA\u2019s Viking landers touched Mars, one question shadows their experiments: Did they miss life, or did they destroy it while trying to prove it was there?<\/p>\n
Dirk Schulze-Makuch, an astrobiologist at Technical University Berlin<\/a>, has proposed that Viking\u2019s life-detection tests may have exposed native Martian microbes to lethal amounts of liquid water. Organisms adapted to an extremely dry world, he argues, might not have survived the treatment intended to reveal their metabolism.<\/p>\n \u201cNASA may have unwittingly uncovered life on Mars nearly 50 years ago and accidentally destroyed it before understanding its significance,\u201d Schulze-Makuch argues.<\/p>\n The idea challenges the assumptions behind the 1976 mission. Viking 1 and Viking 2 carried four experiments designed to search Martian soil for organic compounds, metabolic activity and changes associated with living organisms.<\/p>\n Viking, Gas Chromatograph Mass Spectrometer. (CREDIT: National Air and Space Museum) Four tests produced an uneven picture<\/p>\n The Gas Chromatograph Mass Spectrometer heated soil samples, separated the released compounds and identified molecules by their mass signatures. It found no organic molecules, a result that strongly shaped the original conclusion that Mars was hostile to life.<\/p>\n Later discoveries complicated that interpretation. Martian soil contains reactive compounds, including perchlorates, that may destroy organics when heated. NASA\u2019s Phoenix lander<\/a> detected perchlorate in 2007, offering a possible explanation for why Viking\u2019s instrument found no organic material.<\/p>\n The Labeled Release experiment produced a more provocative result. Viking added nutrients containing radioactive carbon-14 to the soil, then watched for radioactive gases that could indicate microbial metabolism.<\/p>\n Radioactive gas appeared soon after the solution was added. The response initially looked biological, but scientists remained skeptical because the other experiments did not provide matching evidence. Non-biological reactions involving the soil\u2019s oxidizing chemistry could also explain the result.<\/p>\n The Pyrolytic Release experiment exposed soil to radioactive carbon dioxide and carbon monoxide under ultraviolet light. The sample was then heated to determine whether carbon had been incorporated into organic material.<\/p>\n<\/p>\n Some trials detected radioactive carbon, but the result remained ambiguous. Researchers later attributed the response to chemical reactions driven by ultraviolet radiation rather than clear biological activity.<\/p>\n The Gas Exchange experiment added a nutrient-rich solution to Martian soil and monitored oxygen, carbon dioxide, nitrogen and other gases. It detected gas release, but could not establish whether chemistry or metabolism caused it.<\/p>\n Water may have been the wrong test<\/p>\n Schulze-Makuch\u2019s argument focuses on a basic feature shared by several Viking procedures: water. Earth biology<\/a> depends on it, so adding liquid seemed like a reasonable way to awaken dormant organisms and reveal their activity.<\/p>\n Mars may require a different approach.<\/p>\n Schulze-Makuch points to microbes in Chile\u2019s Atacama Desert, where some organisms survive inside hygroscopic rocks. These rocks draw tiny amounts of moisture from the air, creating a narrow refuge in one of Earth\u2019s driest environments.<\/p>\n The Labeled Release Experiment (LR). (CREDIT: YouTube \/ Operational Facts) <\/p>\n Martian rocks could provide a similar setting. If native organisms evolved to survive on trace atmospheric moisture, a sudden soaking might have overwhelmed them.<\/p>\n \u201cOn Earth, abundant with water, it seemed logical to use water in Martian studies, expecting life manifestations in its arid conditions,\u201d Schulze-Makuch commented.<\/p>\n He has also suggested that hypothetical Martian microbes<\/a> might incorporate hydrogen peroxide. Such chemistry could help them attract moisture and might produce gases resembling those detected by the Labeled Release experiment.<\/p>\n The possibility remains speculative. No Martian organism has been confirmed, and the Viking reactions still have non-biological explanations.<\/p>\n A desert flood offers a warning<\/p>\n Evidence from the Atacama Desert supports the broader idea that more water is not always beneficial to organisms adapted to extreme dryness.<\/p>\n The Pyrolytic Release Experiment (PR). (CREDIT: YouTube \/ Operational Facts) <\/p>\n A 2018 study in Scientific Reports examined severe flooding in the desert and reported that up to 85 percent of native microbes were killed. The sudden arrival of water disrupted an ecosystem shaped by long-term aridity.<\/p>\n \u201cJust as humans could drown in vast ocean expanses, adding too much water could have been fatal for potential Martian microbes,\u201d Schulze-Makuch said.<\/p>\n Alberto Fair\u00e9n, a Cornell University<\/a> astrobiologist and co-author of the 2018 research, said he \u201ccompletely concurs\u201d that Viking\u2019s water addition could have killed possible organisms.<\/p>\n The theory is not the only proposal suggesting Viking\u2019s methods may have damaged what they were seeking. In 2018, another group argued that heating soil during analysis could have triggered chemical reactions capable of burning organic matter or possible microbes.<\/p>\n Perchlorate offers a simpler explanation<\/p>\n Other astrobiologists remain unconvinced that Viking encountered life.<\/p>\n The Gas Exchange Experiment. (CREDIT: YouTube \/ Operational Facts) <\/p>\n Chris McKay of NASA\u2019s Ames Research Center<\/a> has argued that perchlorate can account for the mission\u2019s confusing results. When Martian soil containing perchlorate is heated, it can react with organic compounds and produce chlorinated organics.<\/p>\n Viking detected chlorinated organic compounds, but scientists initially dismissed them as contamination from Earth. Later Mars missions showed that such compounds occur naturally on the planet.<\/p>\n \u201cThe discovery essentially resolved the Viking dilemma,\u201d McKay told Live Science, referring to perchlorate.<\/p>\n He sees no need to invoke organisms with unfamiliar chemistry. \u201cTheir rationale is questionable,\u201d McKay said. \u201cThere’s no necessity to speculate about a bizarre life form to justify the Viking outcomes.\u201d<\/p>\n That disagreement captures the difficulty of interpreting the Viking data. Positive signals from one experiment did not align with the lack of organics in another, while Mars chemistry<\/a> proved more reactive and complicated than scientists understood in 1976.<\/p>\n Practical implications of the research<\/p>\n Schulze-Makuch\u2019s hypothesis does not prove that Viking found life. It highlights how life-detection experiments can fail when they assume alien organisms will respond like terrestrial microbes.<\/p>\n NASA’s Phoenix lander found traces of perchlorate\u2014a chemical used in various Earth applications\u2014on Mars. (CREDIT: NASA\/JPL-Caltech\/MSSS) <\/p>\n