With NASA predicting that we will find extraterrestrial life within the next 20 years, all eyes are on our neighbour, the (not so) red planet, Mars. The research being done towards discovering life on Mars is a minefield of conflicting evidence and theories, with some scientists believing we already have indisputable proof that microbes either did or currently do, reside on Mars. So, what is this evidence?
For life to develop as we know it, a number of very specific conditions must come into play, so when searching for hospitable planets, the first things scientists look for are Earth-like atmospheres and planet structures. Most scientists agree that Mars once shared an atmosphere similar to that of Earth. Based on land formations seen on the surface, it’s also believed that most of Mars was once covered in water. This is incredibly important because our oceans control the atmosphere and most likely housed primary life on our planet.
So Mars used to have lots of water, and water is crucial to life, but does it still have water? Some scientists speculate that liquid water could still exist in large underground caverns formed by now extinct volcanos which could house life. Recent findings earlier this year also discovered special salts called perchlorates on the surface of the planet. These salts lower the freezing temperature of water to -70 degrees Celsius, allowing salty films of water to form which could potentially trickle into the soil and reach microbes buried deep in the ground before daytime temperatures cause these salty brines to evaporate.
Methane is arguably the second most important molecule, next to water, when searching for life. 90 percent of all methane produced on Earth is done so by living or dying life, making it a massive flashing beacon for researchers. Earlier this year, NASA’s Curiosity rover caught a concentrated whiff of the gas leading to speculation that it may be escaping from the ground beneath the rover. Sceptics were quick to argue that this may in fact be leaking from Curiosity itself however, and this has yet to be settled.
In 1984, a team of scientists examined the famous Alan Hills meteorite for the first time. Upon inspection, the meteorite from Mars contains what appears to be a fossilised, bacteria-like microbe within its rocky interior. Only a limited number of experiments could be carried out on this fossil due to its finite nature whilst also preserving it, and results came back inconclusive. With a number of scientists pointing out these fossils would be too small to allow life under the theoretical limitations of biology; others claim this is physical proof of past life.
As well as evidence, there have also been a number of experiments carried out. Viking 1, essentially an immobile chemistry lab, landed on the planet’s surface to settle the argument. The lander’s most high profile experiment involved adding sugars to the soil, containing carbon which had been radiolabelled - meaning we can specifically detect particular ‘labelled’ carbon atoms among other carbon-containing molecules. The idea behind the experiment was that if any life was indeed present in the soil, it would use up the sugar and respire carbon dioxide containing the labelled carbon – and exactly that happened.
We have evidence that Mars might indeed be hospitable enough for life. We even have some direct evidence that it may have once contained life, and may still do to this day. It seems the scientific community will remain undecided on the matter unless we find actual, physical life. One problem in the search for life is that most researchers look for life as it is on Earth. Whilst Mars may have once been similar to Earth, it is now its own, distinct planet and life will have evolved differently in ways we may not think possible with our current understanding - we may need to think outside the box to find it.