Article | Microbiology

Life on Mars - perhaps not just a song!

9 July 2021 — Pit Lipscomb (3CC)

Despite the warm red appearance, Mars is a cold and unwelcoming place. The thin atmosphere and the cold temperature, makes liquid water on the Martian surface near impossible. This is bad news for any molecules aspiring to become living organisms, as water is a vital and fundamental building block for life. Luckily there is ample evidence that there is water beneath the surface. It has already been confirmed that several subsurface lakes exist under the Martian ice, but it is presumed that there is much more several hundred meters under the surface.

Water, however, is not the only requirement for life. Any organism needs a reliable source of energy to stay alive. The most obvious source of energy is of course the Sun. It constantly radiates essentially free energy. Of course, an organism living deep underground does not have this privilege. Luckily researches at NASA have found a potential solution to this energy problem. The researchers analysed the chemical composition of rocks that have been flung from Mars to Earth by impacts. They realised that the chemicals in the rock were similar to the chemicals that underground terrestrial microbes use to survive. This could supply any underground life with enough chemical energy to sustain itself.

What does this mean? Any cell must respirate to generate energy (cellular respiration is not to be confused with regular respiration). This process involves using an oxidising agent and a fuel, such as sugar, and converting it into ATP. There are several ways to do this. Cellular respiration can be divided into 3 distinct groups: aerobic respiration, anaerobic respiration, and fermentation. We will be focusing on anaerobic respiration. This method uses any oxidising agent that isn't oxygen, in our case, the potential Mars microbes would use sulphate (\(SO_4^{2-}\)). This means that the microbes use sulphate to “breathe”. These types of microbes are called sulphate-reducing microorganisms, and they have been present on earth for millions of years, thus the possibility of this type of respiration is not at all theoretical.

Where does the sulphate come from? In the deep underground pools, radioactive materials may emit ionising radiation. This means nothing more than the radiation has enough energy to tear electrons out of their orbitals. This energy can convert the surrounding water into hydrogen and oxygen. The oxygen then oxygenates minerals such as pyrite (\(FeS_2\)) in the surrounding rock to form sulphates. The remaining hydrogen is absorbed into the water and can act as the fuel. So, this reaction provides all the necessary components to sustain life, and the paper assumes that it is enough to sustain a large number of organisms.

Of course, this is yet to be confirmed. Though the mechanism is very viable and works here on earth, there is no evidence that this potential has been harnessed by any microorganisms on the red planet. The only way to truly be sure would be to drill deep into the ground and take a look.

Bibliography

  • Anderson PS (2021). Mars Might Support Microbial Life, Deep Underground. EarthSky. [link]
  • Tarnas JD et al. (2021). Earth-like Habitable Environments in the Subsurface of Mars. Astrobiology 21(6). [link]

Cover image courtesy of Pacific Northwest National Laboratory.

Author(s): Pit Lipscomb (3CC)
Editor: Nick Aschman

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