Sponges from Mars? Study suggests water on the planet

Now, a new study, published in Nature Geoscience, surprisingly shows that brine deposits below the surface of Mars, especially near the poles, can contain molecular oxygen – which is crucial for life on Earth. This microbial life or even simple animals like sponges.

The surface of Mars 3.8 trillion to 4 trillion years ago was much like the earth's and would have had the right conditions for life. At that time, it had a thick atmosphere and flowing water on the surface, a global magnetic field and volcanism.

Today, the surface is dry and cold – 5ºC to 10ºC by day and -100ºC to -120ºC at night. In fact, the atmospheric pressure is less than 1% of the Earth's, meaning that any flowing water would quickly evaporate into the atmosphere. But it can be trapped below the surface. Volcanism is also dead and only small-scale crustal magnetic fields remain to protect it from harsh solar radiation in the southern hemisphere. It was for these reasons that it is unlikely that it will be effective.

Mounting evidence

We now know that there are traces of methane on Mars, however, as Mars Express and the Curiosity rover. The source of this methane might be hydrothermal activity, or microbial life. On Earth, flatulent cows alone produce some 25% to 30% of the methane in the atmosphere. Either of these possibilities challenges, but if the source is life that would obviously be an amazing discovery. The Joint European and Russian ExoMars Trace Gas Orbiter is currently investigating the source of this methane.

The NASA Mars Reconnaissance Orbiter also known as "recurrent slope lineae" – streak-like patterns that may indicate briny water seeping to the surface. However there are alternative explanations. Some scientists suggest that these may also just be movements of sand. That said, rovers and landers have found substances including calcium and magnesium perchlorates near the suspected water seeps and other locations on March – and these indicate the presence of brine.

Most recently, the ESA Mars Express mission found radar evidence for liquid water in the south polar region on Mars – potentially a subsurface lake. This water, which also seems to be briny, would be a whopping 20km wide and 1.5km under the surface.

The new study calculated how much molecular oxygen could be dissolved in liquid brines on March. It shows that the small amount of oxygen that is produced in the atmosphere could be broken down into the temperature and pressure of the surface of Mars. Using an atmospheric model, the researchers studied this solubility at different locations of the planet and over time. Liquid environments which contain dissolved molecular oxygen would be scattered over most of the surface of Mars, but it would be more concentrated.

The computer models show that this lead to breathable concentrations of oxygen for any aerobic microbes (bugs that require oxygen). On Earth, life evolved alongside photosynthesis, which provides breathable oxygen for aerobic life. The new results are interesting – they could be created independently of photosynthesis. They can also explain how the oxidized rocks on the planet's surface could have formed.

Leads for space exploration

So how can we find evidence of life? The current Mars missions are providing global information from the surface. Curiosity's discovery that organic molecules may be long lived on Mars. NASA's March 2020 NASA-ESA mission to return to Earth, being planned now.

However, the NASA rovers are designed to drill only five centimeters under the surface. The rover that is part of the ESA-Russia ExoMars 2020 mission that we are working on to be able to drill up to two meters below it. Ultraviolet, cosmic and solar radiation can be found below – providing our best hope for finding life on the planet. The ExoMars rover landing site will be decided by Mawrth Vallis and Oxia Planum, both of these were ancient water-rich environments.

Although the current strategy is to search for signs of ancient life on March, the current life should be detectable too if present. We will have to wait for the ExoMars results to see if of the past or present the biomarkers are present, and the analysis of the returned samples. While the rover is going to be there, there is evidence for other locations too, so it is a good thing that they may be present at the ExoMars candidate sites.

Beyond the current missions, should we be targeting the brines specifically? That certainly would provide tantalizing targets for future missions. The limit of what can be imposed by the difficulty of deep drilling on a planet far away. Drilling up to 1.5km below the surface to sample the lake would be a large scale effort beyond the capability of current technology. The better bet may be considered to be more specific to regions, such as the water seeps.

Another obstacle is the planetary protection rules, which state that you can not risk contaminating an area where there may be extra-terrestrial life with bacteria from Earth. However, the hope is that any Martian life would be hardy enough to meet your expectations, designed and built with strict planetary protection guidelines, will find it.

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Mars could have enough molecular oxygen to support life, and scientists figured out where to find it