Humans have been interested in Mars for a very long time, and it continues to be a prime target for exploration for current and future missions (including, potentially, manned missions on the SpaceX Starship). One of the first missions to Mars took place back in 1976 when NASA sent the Viking lander to the surface of the red planet.

This mission was able to send back the first pictures from the surface of another planet, which was incredible, but the more important experiment may have been its tests for life.

The probe conducted several tests to see if there was any type of biological life on Mars, and the results were conflicting. At the time, the experts ended up determining that they did not detect life, but in a new letter published in Science, modern scientists are questioning that determination.

When it comes to alien life, the most common claim would be that it was a massive government coverup, but that is not the case here. Instead, the scientists think that the data that was gathered was simply misinterpreted. Professor Dirk Schulze-Makuch of the Center for Astronomy and Astrophysics at Technische Universitat Berlin wrote about it in an article for Big Think:

“Even though the very first test at Viking 1’s Chryse landing site had been positive for organic synthesis (with a 99.7% certainty compared to the control sample), follow-on tests provided no clear results. The gas exchange experiment was just as puzzling: It showed the release of several gases, including oxygen, but scientists today still don’t agree on an explanation.”

The experiment in question was conducted by placing nutrient rich water and radioactive carbon (brought from Earth) into the Martian soil. If life were there, the test assumed, it would consume the nutrients and emit radioactive carbon. And that is just what happened on the first test. In the letter, the scientists wrote:

“A substantial amount of radioactively labeled CO₂ was released from C-labeled nutrients in an experiment designed to seek a Martian analog of respiratory metabolism. A substantial release of dioxygen (O₂) and exchange of CO₂ was observed when the Martian soil was humidified, in an experiment premised on the view that soil containing active microbes would exchange gases with the atmosphere, agnostic of its metabolic survival strategy. Thus, by a ‘preponderance of evidence’ standard, Viking had found microbial life on Mars.”

Not surprisingly, the tests were repeated, but the results came back negative. At the time, it was thought that the first test came back positive due to contaminants that were brought from Earth rather than due to biological life on Mars. The questioning team, however, has a different explanation.

They think that the first test produced positive results, but the test destroyed all the life in the sample of Martin soil. While the original researchers assumed that more time and nutrients would benefit the microbes (if they were there), it may have ended their lifecycle. Schulze-Makuch talked with Space.com about this in 2024, giving an easy-to-understand analogy.

“Imagine something similar happened to you [as a human]. For example, if there was an alien in a spaceship coming down to Earth and found you somewhere in the desert. Then they said, ‘OK, look, that’s a human and it needs water,’ and put you directly in the middle of the ocean. You wouldn’t like that, right? Even though that is what we are. We are water-filled bags, but too much water is a bad thing, and I think that’s what happened with the Viking life-detection experiments.”

The team goes on to say that Martian life very well may have evolved to have hydrogen peroxide in their cells, which would help them to survive the very cold environments on the planet. This was written about in a 2007 study by Schultz-Makuch and co-author Joop M. Houtkooper:

“This adaptation would have the particular advantages in the Martian environment of providing a low freezing point, a source of oxygen and hygroscopicity.”

Then, they talked about how this could influence the experiments in another piece for Big Think:

“If we assume that indigenous Martian life might have adapted to its environment by incorporating hydrogen peroxide into its cells, this could explain the Viking results. If the Martian cells contained hydrogen peroxide, that would have [destroyed] them. Moreover, it would have caused the hydrogen peroxide to react with any organic molecules in the vicinity to form large amounts of carbon dioxide — which is exactly what the instrument detected.”

Only future experiments could prove that their theory is correct, but hopefully this letter will encourage future missions to Mars to bring the necessary equipment to conduct those experiments.

If you thought that was interesting, you might like to read about a second giant hole has opened up on the sun’s surface. Here’s what it means.