A new study found that Martian soil is toxic to bacteria, making it even less hospitable to life than scientists previously thought.  A group of researchers found that ultraviolet (UV) radiation streaming from the sun “activates” chlorine compounds in Mars’ soil, turning them into potent microbe-killers. The Nature’s Scientific Reports journal featured their findings on Thursday.

These chlorine compounds, called perchlorates, seem to be widespread in the Martian soil, as several NASA missions have spotted them in a variety of locations.

Image Credit: Mike Ramadan
Image Credit: Mike Ramadan

The perchlorates have several characteristics that would appear to boost the planet’s habitability, as these compounds drastically lower the freezing point of water. They also offer a potential energy source for microorganisms, according to scientists.

Researchers conducted experiments with UV radiation and found that Martian soil is toxic to bacteria

The new study, led by Jennifer Wadsworth and Charles Cockell from the U.K. Centre for Astrobiology and School of Physics and Astronomy at the University of Edinburgh in Scotland, considers perchlorates by using a different approach. The researchers exposed a bacterium known as Bacillus subtilis, a common spacecraft contaminant, to perchlorates and UV radiation at levels alike to those found at and near the Red Planet’s surface.

Wadsworth and Cockell noted that because Mars’ atmosphere is just 1 percent as dense as Earth’s atmosphere, UV fluxes are significantly higher on the Red Planet than on our planet.

“These data show that the combined effects of at least three components of the Martian surface, activated by surface photochemistry, render the present-day surface more uninhabitable than previously thought and demonstrate the low probability of survival of biological contaminants released from robotic and human exploration missions,” wrote the researchers in the study, according to Scientific American.

While scientists already knew about perchlorates’ toxicity, Wadsworth stated that it usually takes high temperatures to “activate” these compounds. She added that it is unclear how deep this inferred inhabitable zone is on the Red Planet because the exact mechanism causing the cell-killing action isn’t understood completely.

“If you’re looking for life, you have to additionally keep the ionizing radiation in mind that can penetrate the top layers of soil, so I’d suggest digging at least a few meters into the ground to ensure the levels of radiation would be relatively low,” Wadsworth told Space.com, according to Scientific American.

Study suggests Martian surface may be highly damaging to living cells

The researchers also found that the effect of perchlorates reacts with two other types of chemicals found on the Red Planet’s surface: iron oxides and hydrogen peroxide. They conducted experiments with the three substances, and the combination led to a more than 10-times increase in death of bacterial cells compared with perchlorates alone.

Scientists have been speculating on the influence that perchlorates may have on the habitability of Mars ever since their discovery there several years ago.

Overall, the new study, funded by the Science and Technology Facilities Council, showed that with UV radiation exposure, magnesium perchlorate becomes capable of killing bacteria much more efficiently than UV light alone. The researchers noted that at concentrations of perchlorates similar to those found on the surface of the Red Planet, cells of B. subtilis quickly died.

Mars' lack of a magnetosphere makes its regolith highly susceptible to UV rays. Image Credit: Kevin Gill
Mars’ lack of a magnetosphere makes its regolith highly susceptible to UV rays. Image Credit: Kevin Gill

Although the Martian surface has long been suspected to have toxic effects, the new study suggests that it may be highly damaging to living organisms or cells, mainly due to a toxic mix of oxidants, iron oxides, perchlorates, and UV energy.

‘It’s important we take all the precautions we can to not contaminate Mars’

The European/Russian ExoMars rover, which is scheduled to launch to Mars in 2020 on a mission to search for signs of life, will also feature a drill that can reach a maximum depth of 6.5 feet (2 meters). The mission, dubbed the ESA mission, is underway and the Trace Gas Orbiter is delivering data to prepare everything for the ExoMars rover.

Wadsworth told the University of Edinburgh News that their findings have important implications for the possible contamination of Mars with bacteria and other materials from space missions. She believes the study should be taken into account in designing missions to Mars.

The researchers noted that there’s an important factor regarding the new results, however: B. subtilis is a garden-variety microbe, and it’s not an “extremophile” adapted to survive in harsh conditions.

“It’s not out of the question that hardier life forms would find a way to survive at or near the Martian surface,” said Wadsworth, according to Space.com. “It’s important we still take all the precautions we can to not contaminate Mars.”

Source: Scientific American