This text was initially printed at The Dialog. The publication contributed the article to House.com’s Professional Voices: Op-Ed & Insights.
Discovering life past the Earth can be a significant scientific discovery with important implications for all areas of science and human thought. But, just one direct seek for extraterrestrial life has ever been performed.
Over the previous half-century, the measurements made throughout the Viking biology experiments have been the topic of many discussions, analyses and hypothesis. Right now, scientists are nonetheless discussing the outcomes of those experiments in an try to reply the age-old query of whether or not there may be life past the Earth.
The yr 2025 marks 50 years because the two spacecraft launched, three weeks aside. These landers achieved humankind’s first two profitable mushy landings of operational and functioning spacecraft on the floor of one other planet.
I am an atmospheric scientist who labored on the Viking missions within the Nineteen Seventies on the NASA Langley Analysis Heart, the laboratory that developed and managed the extremely profitable Viking missions. The Viking missions’ scientific discoveries painted a brand new image of Mars’ environment, floor and planetary historical past.
Launching and touchdown the Viking spacecraft
The 2 Viking spacecraft each consisted of an orbiter and a lander. Viking 1 entered Mars’ orbit on June 19, 1976, and efficiently landed on the floor on July 20, 1976, which was additionally the seventh anniversary of the primary human Moon touchdown. Viking 2 adopted, touchdown on Sept. 3, 1976, at a web site farther to the northwest.
Viking wasn’t simply in search of life.
These crafts contained gear to take photos; map warmth power, wind and climate; examine the chemical composition of the floor, mud and environment; and acquire and analyze soil samples.
Measurements that Viking took of the environment prompt that Mars used to have a a lot denser environment however over time misplaced it. It additionally noticed that the wind picks up tiny mud particles, blowing them into the environment. This course of colours the planet’s sky completely pink.
The Viking landers additionally found that at any location on Mars, the environment’s floor strain varies seasonally. The planet has frozen north and south poles, like on Earth. On the Martian poles in summer season, the frozen carbon dioxide sublimates – reworking from a frozen stable to a gasoline – after which on the winter pole condenses again right into a frozen stable.
That course of, distinctive to Mars, impacts the atmospheric strain by altering how a lot carbon dioxide is in gasoline type as an alternative of stable type over the planet’s floor.
Biology experiments
Every of the three Viking biology experiments introduced a soil pattern from the Martian floor right into a sterilized take a look at chamber and uncovered the pattern to a distinct nutrient underneath completely different atmospheric circumstances.
Researchers needed to search out out whether or not the soil contained microorganisms, so that they monitored how the environment within the chamber modified. Metabolic processes – like respiration – from organisms consuming the nutrient would change the chemical composition of the chamber’s environment.
Relying on the experiment, the nutrient contained both carbon, carbon dioxide or carbon monoxide – all of which had been radioactive. With radioactive samples, researchers may observe the extent of radioactivity within the chamber to see if metabolic reactions within the soil samples had been elevating or decreasing it.
For all three experiments, the researchers may use radio instructions to warmth up the take a look at chamber, which was nonetheless contained in the Viking spacecraft on Mars. This is able to destroy any potential microorganisms within the soil and cease the manufacturing of any gases they had been creating metabolically.
Within the first experiment, known as the carbon assimilation experiment or the pyrolytic launch experiment, the researchers simulated the Martian environment in certainly one of Viking’s take a look at chambers. They stuffed the chamber with gases equivalent to carbon dioxide and carbon monoxide and made these gases radioactive to see how the environment modified from interactions with the soil pattern.
Within the second experiment, The labeled launch experiment, researchers immediately injected the soil pattern with a nutrient containing radioactive carbon. They monitored the experimental chamber for radioactive carbon dioxide and measured the extent of radioactive carbon dioxide after injecting the soil samples. On this experiment, the investigators noticed outcomes that might have come from a organic supply.
The third experiment, the gasoline change experiment, stuffed the chamber with helium, which doesn’t react with something. They uncovered the soil to several types of vitamins. Some had been incubating in moist circumstances, others in humid circumstances and others nonetheless in dry circumstances.
Once more they monitored the chamber for potential metabolically produced gases. When the soil samples touched the moist nutrient, the humidity instantly brought about some adjustments within the chamber’s chemical atmosphere. Most of those adjustments had been simply brought on by the water evaporating.
In a single case, superoxides within the soil, that are O₂ molecules which have taken on an additional electron, reacted with water. Different adjustments needed to do with oxygen molecules within the soil breaking down. All of those modified the environment within the chamber however possible wouldn’t have been brought on by microorganisms.
The researchers repeated this experiment by resetting the chamber’s environment and including in recent vitamins, however they did not change the soil pattern. This time, the soil launched solely carbon dioxide into the chamber, which possible got here from the natural supplies within the nutrient they added breaking down.
The outcomes from this third experiment led the researchers to conclude that there possible weren’t microorganisms within the soil. However collectively, the outcomes from the three experiments weren’t precisely simple.
Solely the labeled launch experiment outcomes prompt a organic supply for the noticed outcomes. The carbon assimilation experiment and the gasoline change experiment prompt that nonbiological or inorganic chemical reactions brought about the noticed outcomes.
Lead researchers on the undertaking concluded that there was no unambiguous discovery of life by the Viking landers, however it can’t be fully dominated out.
The molecular evaluation experiment
In contrast to the biology experiments, which experimented on soil samples, one other Viking experiment, the molecular evaluation experiment, immediately searched the Martian floor for natural matter. Natural supplies are carbon compounds bonded with hydrogen, oxygen or nitrogen that come both immediately or not directly from residing organisms.
To everybody’s shock, this experiment didn’t detect any natural compounds on the floor of Mars. Researchers had identified for years that meteorites containing natural supplies had hit Mars repeatedly all through its historical past, so to search out none in any respect appeared unusual.
Some scientists theorized that Martian soil may comprise a compound that shortly converts any natural materials on the floor to carbon dioxide. A compound like this could have evaporated any proof earlier than scientific devices had the prospect to search out it.
In 2008, a long time after this discovering, NASA discovered a compound that could be doing simply that. Their Phoenix lander detected excessive concentrations of a compound known as perchlorate within the soil.
When perchlorate is heated – because it was within the Viking molecular evaluation experiment – it could actually chemically destroy natural compounds, and scientists figured it’s the possible offender behind the unusual outcome from the molecular evaluation experiment.
A brand new mannequin for all times on Mars
Scientists are nonetheless utilizing the findings from these experiments at this time. Lately, Steven A. Benner, the director of the Basis for Utilized Molecular Evolution, developed a brand new mannequin for present-day life on Mars based mostly on the three Viking biology experiments’ measurements.
His mannequin predicts that microorganisms may have used the radioactive carbon nutrient within the experiment chamber to create their very own meals, releasing radioactive carbon dioxide within the course of. It additionally means that at night time, microorganisms might be absorbing oxygen and expelling carbon dioxide. That would clarify the oxygen launched from the Mars soil pattern when moistened.
The Benner mannequin means that there might be residing microorganisms on the floor of Mars, however future analysis and measurements might want to verify this very intriguing risk.
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