Mars is full of secrets and mysteries. The classic definition of a desert world, our planet’s arid sibling is a parched wilderness of dunes and planetwide dust storms. With a thin carbon dioxide atmosphere and only 38% the gravitational pull of Earth, there are a lot of puzzles about this cold and frosty little planet, and a lot of scientists who are longing to solve them.
By now, anyone keeping up with the news is bound to have heard that NASA’s Curiosity rover made a flawless descent through the atmosphere of Mars and is now busy eyeing up its new home in the Gale Crater. As was discussed previously here on Australian Science, a big question still on everyone’s mind is the same one which David Bowie sang about back in 1971. Is there life on Mars? However, it seems that NASA’s plans are not to answer this question directly. John Grotzinger, project scientist for the Curiosity mission, is quoted as saying; “Curiosity is not a life detection mission. We’re not actually looking for life; we don’t have the ability to detect life if it was there.” Instead, the main objective of Curiosity is to look for signs of life.
The trouble is that looking for life directly is a difficult task. Back here on Earth, new discoveries are still being made frequently, with life being found in environments and habitats where no one was expecting. There’s a lot which we still don’t fully understand about life here on our own world. When we’re talking about another planet, it’s safe to say that all bets are off. As a result, Curiosity’s goal is to look for the various elements and chemical compounds which life might use – or might have used once upon a time when the planet may have been more hospitable. The focus has shifted from the search for life on Mars right now, to life which may once have lived there.
One point which is worth remembering right now, however, is that there’s one big unsolved mystery about Mars. A gaseous mystery. Large quantities of methane have been detected in the martian atmosphere, which gives rise to a real puzzle. Methane is destroyed by sunlight, and with the thin atmosphere found on Mars, any methane should be rapidly broken apart by solar ultraviolet. The only possible conclusion is that the methane seen on Mars is being replenished somehow. There are only really two possibilities for how this might happen.
One scenario sees the martian methane caused by a geological process called serpentinisation. This is where a type of mineral known as olivine (more familiar to us as the gemstone peridot) chemically reacts with water and carbon dioxide. The reaction creates methane and a green mineral called serpentine (commonly found in certain parts of Western Australia and Tasmania), and releases methane gas. If this is the process which is occurring, it would mean that not only is there a suitable amount of water somewhere under the surface of Mars, but there must also be geological activity for that water to continue being brought into contact with further olivine to react with. This would suggest that there are things which we don’t know about current geological processes on Mars.
The other possibility, more radically, is that this methane is being produced by life. Here on Earth, bacteria known as methanogens are responsible for most of the methane present in Earth’s atmosphere. In fact, on Earth, methane is so regularly produced by living organisms that it can used as an indicator of biological activity.
When three distinct plumes of methane were discovered on Mars in 2009, it was noted that there was an equal probability of either of those two scenarios being the source of the methane – and that both would be huge revelations in our understanding of our neighbouring world. So maybe the Curiosity rover isn’t set up to hunt for life, and maybe it won’t be directly looking for it. But I, for one, do hope it finds some clues about the origin of the mysterious martian methane. Just as any scientist should, I love a good mystery!
Top – NASA JPL/Cornell
Middle – ESA/DLR/FU Berlin (G. Neukum)
Bottom – NASA