Extraterrestrial Zoology: Mars

Since the subject of life on Mars has been well-documented, I won't linger long on the topic, but present a brief overview, as no guide of extraterrestrial life would be complete without a mention of Mars.

A brief history of life on Mars

We have long been fascinated by the idea of there being life on the Red Planet. The popularity of the concept of Martians underwent a mass explosion during the 19^th century. It was theorised by scientists of the time that Mars was a dying world which was slowly becoming cooler and drier, and was the home of a civilization which was attempting to communicate with Earth. It was even suggested that a set of giant mirrors should be constructed in Texas so that we might signal to our Martian friends.

The idea of Mars being a dying planet was reinforced in novels such as H. G. Wells' The War of the Worlds, in which he depicts the Martians invading Earth.

It wasn't until more modern times that we finally recognised Mars not as a dying world inhabited by strange beings, but as a barren landscape on which life was impossible. 

. . . Or was it?

 Is it possible?

The argument for the habitability of the Red Planet was that liquid water once existed on the surface of Mars, and water is, according to our current scientific understanding, essential to life as we know it. Canyons and dried up riverbeds carved by flowing water can be seen on Mars, clear evidence that rivers once flowed across the planet. Indeed, the planet is in the habitable zone – or Goldilocks zone – along with Earth and Venus. Scientists are now fairly certain that Mars was once a watery, habitable world not unlike our own planet. There's a catch,though. New studies on Martian rocks suggest that water was most likely too acidic and salty for most life to exist there, and that only a few Earthly microbes would even have a chance of surviving these conditions. I have to say, although this piece of evidence towards the lack of life is interesting, I'm not convinced. After all, we're not talking about life on Earth, are we? We're talking about Martian life. It is feasible that a native Martian microbe could have evolved to be an extremophile – in other words, an organism adapted to survive extreme conditions. These Martian organisms could have evolved a resistance to briny and acidic conditions, making it a halophile (an organism that can surive and thrive in very salty conditions. Earthly examples of these include Halobacterium, Nitzschia, Wallemia icthyophaga, and others).

But anyway, does it really matter? Watery Mars existed more than 3.8 billion years ago, and we don't really care about microbes that could have hypothetically existed then. Well, it does matter, for 2 reasons. If we found fossil microscopic organisms on Mars, then this would still be an immense scientific breakthrough – it would prove, once and for all, that life can and does exist on other planets. But besides that, if life could have once lived on Mars, then is it possible that life could have survived the drying-up of Mars and lives on today?

Life underground

The surface of Mars is not a nice place for an organism. It's cold, and it's being showered with radiation – and no rover has yet found any solid evidence of an organism on the surface. Therefore, it seems more likely that if life does exist on Mars, then it will be present under the surface. Past volcanic activity could have feasibly created underground caverns and openings, creating aquifers, which in turn form pools of salty water, filled with essential minerals and possibly heated geothermally. If this turns out to be true, then we may well find halophilic organisms in these underground pools.

If we are to speculate a little more, then we might ask ourselves, what are the organisms down there feeding on? There's no sunlight, so there's no chance of photosynthesizing algae-like species. A clue to a possible solution lies with an odd looking organism called Acidithiobacillus thiooxidus, a form of bacteria which forms biofilms which drip from cave ceilings and resemble mucous, earning them the nickname 'snottite'. It gains energy from sulphur compounds, and its waste product is sulphuric acid. Other organisms use iron and manganese, oxidizing it, and they gain small amounts of energy from this. These microbes are using the elements in the stone around them to get energy and perform bodily functions.

It's easy to imagine Martian microbes using a similar process to use the stone around them and what's in it to gain energy.

Who knows? Maybe there is microscopic life living under the surface of Mars, in salty, acidic caves, oxidizing elements in the stone around them to survive.