The methane mystery has attracted much attention over the years because most of Earth's methane is produced by living organisms. While methane can be created by geological processes, what has stumped scientists is the variance in the volume of methane in Mars’ atmosphere.
Mars has a very thin atmosphere – almost non-existent by Earth standards. It’s also not a particularly hyperactive world, with dust storms, well-studied polar ice variations, and so on being the only “changes” scientists have recorded over the past few decades of studying the planet. The discovery of large variations in anything, let alone oxygen and methane, which are both biomarkers and indicate the existence of life, is therefore a very big deal.
The oxygen spikes, in particular, are exciting scientists from almost every field. Geologists are jumping into the debate through the most logical explanation that the oxygen is being produced by geological processes. The fact that this oxygen is being produced at extremely low temperatures is exciting experts in organic chemistry, because low temperatures typically don’t encourage the release of oxygen on Earth, and astrophysicists and astrobiologists are enthusiastically pouring over all of the new data to try and understand the Martian environment better.
One thing they all agree on is that whatever is creating the variations of oxygen and methane on Mars, it's definitely not a known process. They are hoping that when the Mars 2020 mission lands with rovers equipped with better tools, we will be able to at least pinpoint whether it is a geological or biological process.
The possibility that biology is behind the changing levels of the gas in the Martian atmosphere can't be ruled out, but the fact that it is a very remote possibility is not deterring those who are already predicting the discovery of life on Mars. The discovery of huge volumes of live biota in the Earth’s crust is fuelling this theory, as active organic chemistry underground would be the simplest explanation.
The Mars 2020 mission’s primary focus will be to discover signs of past microbial life, which may lead to definitive answers. We know that between 3 billion and 4 billion years ago the Jezero Crater on Mars featured a river that flowed into a body of water that measured approximately 500m2. This river deposited delta sediments packed with clay and carbonate minerals, creating the ideal condition for stromatolites to form on the shorelines. Stromatolites are layered mounds, columns, and sheet-like sedimentary rocks that were originally formed by the growth of layer upon layer of cyanobacteria, a single-celled photosynthesising microbe.
The rocks around the Jezero Crater show evidence of carbonate and hydrated silica – molecules that are known on Earth to help preserve microscopic fossils over billions of years. In addition to preserving signs of ancient life, carbonates can teach us more about how Mars transitioned from having liquid water and a thicker atmosphere to being the freezing desert it is today. Carbonate minerals formed from interactions between carbon dioxide and water, recording subtle changes in these interactions over time. In that sense, they act as time capsules that scientists can study to learn when- and how- the Red Planet began drying out.
Whatever we learn over the next few years, each discovery brings us closer to making Mars a more habitable planet for humans, and a more realistic exploration destination than it currently is – despite grand plans to pup people on Mars in the next decade.