Research into trace gases in the Mars atmosphere, for instance ground based studies of the martian atmosphere, have suggested that tens of parts per billion of the molecules might be methane. In addition it has been suggested that there might be seasonality in the distribution of methane. This is exciting and extraordinary, because one (but by no means the only) explanation for the presence of methane is that it is associated with microbial activity at some point in Mars’ history. Thus this is an important science topic for MSL.
Stable isotopes and some carbon-based molecules including methane are measured with the Tunable Laser Spectrometer (TLS), which is part of the SAM instrument suite in Curiosity. The spectrometer is built as a two channel ‘Herriott Cell’ design. Generally, a Herriott cell is made of two opposing mirrors with a hole for the laser input and output. The basic idea for this goes back to the 1960s. In the case of the Curiosity spectrometer, one detector channel is at a wavelength of 3.27 µm for the detection of methane, the other channel is at 2.87 µm for the detection of carbon dioxide and water (these are infra red wavelengths). The detection limit for methane is about 2 parts per billion. However, this could be improved during the MSL mission experiments, perhaps by as much as up to a factor of 100.
So far we have not detected methane, which highlights the importance of lander-based studies in addressing these science issues. Curiosity will continue to accurately check the composition of the Mars atmosphere – could the composition change with season as previously suggested by the ground-based studies? Curiosity and the SAM team will get to the bottom of the issue.
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