The main test the two Viking landers conducted was called the Label Release Experiment. It involved testing a sample of soil dug up from the surface. The soil was placed in a sealed compartment on board the lander. A dilute aqueous solution with uniformly labelled carbon compounds was added to the soil. The atmospheric output of the soil was measured to monitor the appearance of radioactive gasses. The experiment was then repeated using a second soil sample heated to 160 degrees Celsius (320 Fahrenheit). The atmospheric output was measured again.

At the time although the data indicated microbial life might have produced the results seen, NASA chose to err on the side of caution and not announce life on Mars in the present. Revisiting the data from the two Viking landers years later produced a different conclusion that the evidence of microbial life on Mars was 99% certain.

A new report suggests that the Viking lander experiments killed the life it extracted from the samples according to Dirk Schulze-Makuch, an astrobiologist at the Technische Universität Berlin in Germany. In a commentary appearing in the September 27, 2024 edition of Nature Astronomy. Dirk writes that the use of liquid water in the experiment was a mistake.

Why? Martian conditions are drier than any desert on Earth, and in the driest desert, the Atacama in South America, microbes draw their water not from liquid but from salts that absorb moisture from the atmosphere. The presence of water is toxic to these microbes, with Dirk noting that even one drop could kill.

Dirk believes that following NASA’s liquid water strategy to find evidence of life on Mars and elsewhere in the Solar System may be wrong. He suggests following the salt approach.

Dirk believes that Mars had lots of surface and subsurface water around 4 billion years ago. Over time, with a limited magnetic field to protect the planet from solar and cosmic radiation, Mars lost much of its atmosphere and became a perpetual cold desert. Any life that started on Mars back then would have adapted to the planet’s drying out.

In studies in the Atacama after rare torrential rains, scientists have observed that 70 to 80% of indigenous bacteria die from too much water. Dirk believes that’s what happened to the microbial life on Mars when exposed to the Lab Release Experiments conducted by the two Viking landers.

The salts that could sustain microbial life on Mars are abundant and include sodium chloride, potassium chloride, chlorates and perchlorates, the latter viewed as a problem for life here on Earth when too much is in the environment. Chlorates and perchlorates hold liquid in much lower temperatures which could make them ideal sources for microbial Martian life.

Several decades after the two Viking landers created controversy, NASA sent a series of rovers to follow the water strategy in the search for past rather than present life on Mars. It seemed like a step back in the search for alien life elsewhere in the Universe. Nevertheless, that has remained the current approach NASA has taken.

The two current active rovers, Curiosity and Perseverance have shown us pictures of old riverbeds on Mars as well as eroded landscapes that appear to have been shaped by wind and water. Where Curiosity’s mission has focused on the habitability of Mars in the past, Perseverance has in its experiments and instrumentation the means to hunt for ancient Martian life and collect specimens for later retrieval. In this pursuit, Perseverance has found carbon-based molecules, in other words, organics using an onboard instrument called SHERLOC which is an acronym for Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals. States Ken Farley, a Perseverance project scientist, SHERLOC is “really the only instrument that we think has a reasonable chance of finding organic matter at the concentrations that are likely present” on the Martian surface today. SHERLOC results have been described in a paper published in July 2023 in the journal Nature.

Perseverance landed in the Jezero Crater where past evidence of flowing water features are visible. Although the SHERLOC instrumentation isn’t focused on following the water strategy of NASA’s past, in choosing this landing site it certainly suggests NASA continues to be wedded to that approach in its search for life.

For me, the fact that NASA after Viking decided to focus on past habitability seems a misdirection in our search for alien life elsewhere in the Universe. NASA appears to have forgotten the Viking experiments that a new theory suggests may have killed the life it found in two scoops of Martian soil because it chose water rather than water-containing salts in its Lab Release Experiment.

We shouldn’t forget that NASA’s Mars Exploration Program has the ultimate goal of sending humans to the planet. When we introduce humans to Mars a vast biome of exotic life including the microflora and fauna populating our bodies will accompany us along with the water contained within us. Human bodies are 60% water for adult men and 50% for women. How will we protect Martian life from being wiped out by exposure to not just the water but the microflora contained in us?

In a posting about concerns for Martian life that I posted to this site in May 2021, I described the cautionary tale involving the European discovery of the Americas that wiped out 90% of native Americans and a significant amount of the non-human biology of the two continents within a century. Imagine just how disruptive to existing Martian life will we humans be when we land on the Red Planet in the coming decades. I would venture we will probably be far more destructive to Mars than Europeans were to the Americas.

Going to Mars Never Turned into a Space Race

Although the Soviet Union included Mars as a primary mission goal in its exploration of the inner planets of the Solar System, it enjoyed far greater success in getting to Venus, and very little success when trying for Mars. Why was that?

Engineers state that getting to Venus is easier than going to Mars. Venus is closer, easier to approach, requires less on board fuel for boosting the spacecraft further from the Sun as well as for mid-course corrections. Launch windows for Mars open every two years. Launch windows to Venus are far more frequent and longer in duration. Mars missions are significantly more expensive to mount because of the greater distance. With more financial resources to apply to space exploration than the Soviets the United States has reaped the benefit and become the prime explorer of Mars, not that the Soviets haven’t tried.  But after four unsuccessful attempts in the 1960s they ceded Mars to the Americans.

The Technology of the 1960s that Got us to Mars

With Mariner-4 in July 1965 we witnessed the first close range images of Mars as the American spacecraft passed within 10,000 kilometers (6,200 miles) of the Martian surface. To get Mariner aloft the Americans used the Atlas Agena-D multi-stage rocket, the workhorse of the early 1960s unmanned and manned space program. Like their Soviet counterparts the Americans realized a direct path to Mars was best managed by first putting the spacecraft into Earth orbit before injecting it into a rendezvous trajectory aimed at Mars.

This first Martian explorer used four solar panels containing over 28,000 cells to keep its instrumentation operating throughout the seven month journey to the planet.  The frame was magnesium to which the solar panels, antennae, TV camera, mid course propulsion system, and attitude control nitrogen gas jets, three gyros and regulators were attached. The science package included a magnetometer, dust detector, cosmic ray telescope, trapped radiation detector, solar plasma probe, and ionization chamber. Navigation positioning used sensors that located the Sun, Earth and Mars’ positions and the star Canopus. The telecommunications equipment included high and low gain antennas and a tape recording system for delayed transmission. The software command subsystem recognized 29 direct command words or 3 quantitative word commands. To keep the instrumentation from freezing or boiling the American engineers built into the spacecraft frame a series of adjustable louvers for climate control, insulating blankets to ward off the cold, and polished aluminum shields to keep the Sun-exposed side of the spacecraft cool.

The first images from Mariner-4 (see above) showed 1% of the planet’s surface, a heavily cratered area that gave us a picture of Moon-like desolation. Mars surface atmospheric pressure readings were 4.1 to 7.0 millibars (compare that to an average of 1,000 millibars at sea level on Earth) and daytime temperatures of -100 degrees Celsius (-148 Fahrenheit). No magnetic field was detected.

Even after completing its Martian flyby Mariner continued to transmit until December 1967. The cause of its demise was recorded by the on board cosmic dust detector, a micro-meteoroid shower that damaged the thermal shield, attitude control and data transmission.

Revisits to Mars by two Mariner spacecraft in 1969 enhanced our picture of Mars as they flew over the equator and south polar regions of the planet and provided further analysis of the Martian atmosphere and surface conditions. The images captured by Mariners’ on board cameras continued to reveal a cratered landscape but atmospheric telemetry revealed suspended dust, CO2, H2O, CO, and ionized hydrogen and oxygen. Equatorial surface temperatures reached a benign 17 degrees Celsius (63 Fahrenheit) in the daytime.

Mariner-9 Becomes the First Artificial Martian Satellite

Mariner-4 demonstrated successful technology design for Martian missions and became the template for subsequent flights to Mars and planets further out. One of these was Mariner-9, one of two space missions planned to orbit Mars.The first, Mariner-8, experienced a launch failure. NASA quickly redesigned the Mariner-9 mission to compensate for the loss.

Unlike other interplanetary and lunar missions Mariner-9 followed a direct ascent trajectory from Earth to Mars arriving after a 167-day flight. This method was chosen to preserve fuel.

Orbital insertion involved firing of on board rockets several times to create ideal positioning for imaging and data transmissions to Earth. This technological feat was the first of its kind. No earth-launched spacecraft had ever orbited another planet.

When Mariner-9 arrived in September 1971 a planetary-wide dust storm made it impossible to obtain images of the surface. All that could be seen were the summits of  four large volcanoes never observed before. These were Olympus Mons and the three Tharsis peaks. By December the storm abated and Mariner started sending images and relaying telemetry. During its 13-month mission Mariner sent 7,329 images covering the entire planet until running out of fuel. It remains in Martian orbit today and its orbit will degrade sometime around 2022.

Mariner-9 gave us an entirely new perspective about Mars. Its images showed ancient river beds and many other flow features indicating a past that included free-flowing water on the surface. Valles Marineris as seen in the picture above proved to be a canyon larger than anything on Earth. Mariner-9 took pictures of wind-eroded sediments and witnessed weather system changes including morning fog. No longer was Mars seen as Moon-like.

The Soviets Duplicate the Feat of Mariner-9

In 1971 the Soviet Union launched an even more ambitious attempt to both orbit the planet and land upon it. They launched two orbiters, Mars-2 and Mars-3, each including a lander for studying and observing the Martian surface . Entering orbit in November Mars-2 included an on board camera and a scientific instrument payload. The Mars-2 lander, crashed in attempting a controlled descent. The Mars-3 lander achieved a soft landing and within a minute fell silent. The global dust storm enveloping Mars at the time was believed to be the cause of failure.

The Soviets continued to launch a Mars series of robotic spacecraft through 1972 and 1973 experiencing more failures than successes. Their technology for Martian landings did not work. Chip degradation during the long spaceflight was believed to have been one of the causes of failure with both the orbiters and landers. After 1973 the Soviet program stopped.

The Vikings Land on Mars

In the Bicentennial year of 1976 the United States accomplished two successful landings on the Martian surface. Viking-1 and Viking-2 were a combination of orbiters and landers. The Americans may have learned from the Soviet attempts at soft landings. The Soviets released their landers before their Mars spacecraft entered orbit. Every landing attempt either failed to touchdown properly or stopped transmitting shortly after arrival. The American answer was simple. Bring the entire spacecraft into an orbit around the planet. Have the orbiter photograph potential landing sites and then program the lander to make the descent to a site deemed safe.

Both Viking spacecraft, orbiters and landers were successfully deployed. Unlike previous Mars missions Vikings used Titan-IIIE-Centaur heavy-launchers to boost them into earth orbit before the Centaur stage placed them into an Earth to Mars trajectory. Both orbiters based their design on the Mariner-9 spacecraft but were much heavier, weighing 3,530 kilograms (7,766 pounds). The orbiters, in addition to performing reconnaissance on site selection for the landers, also acted as communications relays to transmit data from the landers back to Earth.

Both landers were timed to arrive on the planet surface in celebration of the July 1976 bicentennial and both achieved successful landing using heat shield technology, aerobraking, first practiced on Venus missions, parachute deployment followed by retrorocket fire to achieve controlled touch downs.

There remains controversy over findings from the landers’ scientific experiments. The experiments were specifically designed to study the biology and organic and inorganic chemical composition of Martian soil samples. A sampler arm with shovel scooped up a small amount of soil and placed it in an environmentally-controlled compartment where it was subject to three experiments. One of those, the Labelled Release experiment, designed by Dr. Gilbert Levin, obtained results that strongly suggested microbial metabolism. But another experiment designed to detect organic molecules found none. At the time it was assumed that a previously unknown chemical in the Martian soil was mimicking microbial metabolism. At the time of NASA’s announcement of experimental results it was not disclosed that on Earth in similar tests in Antarctica Dr. Levin’s experiment showed microbial metabolism while the organic molecule detection experiment found nothing. The controversy over Levin’s experiment continues to this day with a number of journal articles suggesting that there was and is no support for chemical agents being the cause of the observed response on Mars. More recently Martian orbiters, landers and rovers have uncovered evidence that water in liquid form exists on Mars and that Dr. Levin’s conclusions that rudimentary microbial life exists may have been right after all.

We will continue exploring Mars in our next space blog. So please stay tuned and join the conversation giving your opinion on whether life still exists on Mars today.