No methane found on Mars, needed for life
Since its dramatic landing in the seven minutes of terror almost three months ago, the Curiosity rover has been living up to its name, examining Mars to the finest minutiae. Its arsenal of instruments include a rock-vaporizing laser, a scorching oven, multiple cameras, and a laser spectrometer.
Over the past week, data has been returning from the Tunable Laser Spectrometer (TLS), which analyses the composition of the Martian atmosphere. The results are not unexpected – the Martian atmosphere is about 96% carbon dioxide, with a dash of other gases.
Disappointingly, however, methane was not amongst the trace gases found. Methane, the simplest hydrocarbon with the chemical formula CH4, is considered widely as a biomarker indicative of the existence of life. Unlike other atmospheric gases, methane is not stable. In Earth’s atmosphere, free methane reacts with oxygen, producing carbon dioxide and water. Methane is also broken down by ultraviolet light from the sun. Scientists estimate that, on average, a methane molecule is degraded after a mere ten years in the atmosphere.
On Earth, atmospheric methane is replenished by a plethora of sources. Microorganisms produce methane as a byproduct of metabolism; decomposing and fermenting biomass release methane; animals of all kinds produce methane in their digestive systems; human mining of natural gas fields release methane from underground reservoirs. The common link between all these processes is that they are all related to life. Finding methane in the Martian atmosphere greatly increases the probability that life exists on the red planet.
Yet, not all hope is lost. Methane is not a fool-proof indicator of life. Some life does not produce methane, while various inorganic processes do. The lack of methane does not rule out the possibility of life.
The simplest explanation may be that Curiosity just happened to be in the wrong place at the wrong time. Other probes, such as the Mars Express Orbiter, have detected trace amounts of methane in the atmosphere of Mars. However, because of the speed at which methane degrades, it does not have the time to spread across Mars. Underground reservoirs unfreeze and release methane during the summer, and Curiosity landed at the end of the Martian winter. It may be that Gale Crater, Curiosity’s landing site, just does not have methane.
Undeterred, Curiosity continues its mission to explore Mars. Other instruments, including a mass spectrometer and a gas chromatograph, will also study the atmosphere, perhaps picking up methane that TLS has missed. In the upcoming weeks, Curiosity is set to examine its first soil sample to search for signs of life in the ground. Life just may exist on Mars, waiting to be discovered.