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Mars has long been thought of as dry and barren – unable to harbour life. But research over the past few years indicates that there is most likely some briny water present there today, including a possible subsurface lake. This has led to new hopes that there could actually be life on the red planet after all, depending on what the conditions are like in the water.


Mounting evidence


We now know that there are traces of methane on Mars, however, as discovered by Mars Express and the Curiosity rover. The source of this methane might be either hydrothermal activity (the movement of heated water), or microbial life. On Earth, flatulent cows alone produce some 25% to 30% of the methane in the atmosphere. Either of these possibilities challenges our current understanding of the red planet, 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 discovered seasonal features called “recurrent slope lineae” – streak-like patterns which 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 at other locations on Mars – and these indicate the presence of brine.


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


However, the NASA rovers are designed to drill only five centimetres under the surface. The rover that is part of the ESA-Russia ExoMars 2020 mission that we are working on will be able to drill up to two metres below it. This will get below where ultraviolet, cosmic and solar radiation can penetrate and harm life – providing our best hope of finding life on Mars of any planned mission. The ExoMars rover landing site will be decided in November from two current candidates – Mawrth Vallis and Oxia Planum, both of these were ancient water-rich environments.

然而,美国宇航局的探测器被设计成仅能钻探到表面以下5厘米。作为欧洲航天局-俄罗斯ExoMars 2020计划的一部分,我们正在研制的探测器将能够在火星表面往下钻探两米。这将低于紫外线、宇宙和太阳辐射能穿透并伤害生命的地方——为在火星上发现生命提供我们的最佳希望。ExoMars探测器的着陆点将在11月决定,将在 Mawrth Vallis和 Oxia Planum这两个地方选择一个,它们在古代都水量丰富。

Although the current strategy is to search for signs of ancient life on Mars, current life should be detectable too if present. We will have to wait for the ExoMars results to see if signs of either past or present biomarkers are present, and in the longer term analyse the returned samples. While the rover won’t go to the lake or the water seeps, there is evidence for brines at other locations too, so there is a good possibility that they may be present at the ExoMars candidate sites.

Another obstacle is the planetary protection rules, which state that you shouldn’t 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 populate other areas and that our missions, designed and built with strict planetary protection guidelines, will find it.