Mars could have had underground life for millions of years

The surface of Mars, imitated by Curiosity. (Credit: NASA)

For decades, scientists have scanned the surface of Mars for signs of ancient life. But by digging deeper, they encounter historic living areas in unexpected places.

After expanding their research, a team of researchers discovered that the ancient basement of the red planet could harbor microbial life for hundreds of millions of years. By borrowing hydrogen with water, microbes could have enough energy to survive not only underground, but also for miles beneath the surface. If this is true, future missions could look for areas where the basement is now exposed and possibly prove the existence of Martian life once and for all.

The study, conducted by researchers from Brown University and published in Scientific letters of the Earth and planets, was inspired by a curious phenomenon on Earth. Large communities of underground microbes live in the dark without access to the chemical energy of the Sun, the only source of energy for most organisms on the planet. These enterprising bacteria, however, survive by destroying the hydrogen electrons of the water molecules that seep into the subsoil, a process that produces enough energy for them to live.

Obviously, Mars does not have the surface water needed to support life these days, but with obvious signs of historic water, this is probably the case. Similar microbes would have theoretically existed there as well.

Unexpected benefits

Despite difficult conditions, the extremely thin atmosphere of Mars and the intense radiation would have really supported these ecosystems. When radiation reaches surface water, it triggers a process called radiolysis, in which water molecules break down into hydrogen and oxygen. Once the molecules are down, the microbes can easily use molecular hydrogen to fuel their existence.

To find out if these underground communities could have existed, the research team looked at three different factors. First, they used data from the NASA Mars Odyssey spacecraft's gamma-ray spectrometer to determine the abundance of thorium, potassium, and uranium in the Mars crust. These elements emit radiation when they degrade, triggering radiolysis. They are also disintegrating at constant rates. By calculating their current abundance, they can estimate how much radiation has fallen into history.

The lake beds and the dried rivers tell us that there is no shortage of water exposed to radiation, but the team still needs to know how much is absorbed by the soil. To do this, they used density measurements to see how porous the crust of Mars was, which allowed them to estimate how much hydrogen was flowing in the subsoil. The last step was to look for underground areas with a comfortable temperature. They used geothermal and climate models to see which areas were hot enough to hold liquid water, but were not so hot that the heat of the heart of Mars would harm the ecosystem.

With NASA's HiRISE camera, the image shows Syrtis Major, a volcanic area that exposes the ancient basement of Mars. The area is currently considered a landing site for NASA's Mars 2020 rover. (Credit: NASA / JPL-Caltech / University of Arizona)

Animated beginnings

After adding these factors, researchers discovered that about 4 billion years ago, the Martian subsurface absorbed enough hydrogen to energize microbes for hundreds of millions of years . Their model shows that ecosystems extend for several kilometers in the basement and could withstand warmer and colder conditions than expected. In fact, thick layers of ice have trapped hydrogen molecules in the soil, making extremely cold regions the ideal focus for starving microbes.

"People have the impression that a cold climate in early March is bad for life, but what we are showing is that there is more chemical energy for life underground in a cold climate," said Jesse Tarnas, Press Statement. "We think this could change people's perception of the relationship between climate and life on Mars."

However, there are many factors to consider. The study assumes that the Martian microbes resembled those of the Earth, whereas they could have behaved completely differently. Moreover, the existence or not of any life on Mars is still unknown. But to show that he would have had enough energy to survive is another encouraging sign of extraterrestrials.

The only way to prove this theory is to study areas where the basement is now exposed, such as meteorite impact craters. Fortunately, NASA's March 2020 rover will soon be moving towards the red planet and will use this new data to continue our endless search for Martian life.