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Fresh Insights on Martian Methane

In this month's post, we review one of the most exciting discoveries made in our Solar System: the detection of methane gas on Mars. This story started in earnest over twenty years ago when, in March 2003, the newly arrived Mars Express orbiter from the European Space Agency (ESA) started picking up faint traces of the gas in the Marian atmosphere. This detection was done by the spacecraft's Planetary Fourier Spectrometer (PFS), and the ratio was 0 to 30 parts per billion by volume.

Even if these concentrations are minuscule, scientists were greatly excited by this discovery as methane is a compound with potential biological origins. Also, the gas readily breaks down in the Martian atmosphere, suggesting the presence of an active source.

And then the Curiosity rover arrived on the scene. Several months following its touchdown in Gale Crater, the Tunable Laser Spectrometer (TLS) instrument in the portable chemistry lab, known as SAM, or Sample Analysis at Mars, began registering methane levels averaging one-half part per billion by volume, punctuated by spikes of up to 20 parts per billion by volume, suggesting Mars undergoes a seasonal methane cycle during late northern summer.

The significance of methane detection on Mars prompted the European Space Agency (ESA) to launch their next Martian orbiter, the ExoMars Trace Gas Orbiter (TGO), in 2016. The mission's primary objective is to study methane and other gases present in the Martian atmosphere. However, despite years of searching, it has not been able to detect methane. In fact, methane hasn't been detected anywhere else on Mars since Curiosity. (The Perseverance rover in Jezero Crater doesn't have a methane-detecting instrument).

So, what is happening at Gale Crater?

A recent study seems to have shed some light on the release mechanisms of methane at Gale Crater. Scientists believe that salt minerals within the Martian regolith such as perchlorates and sulfates, are forming layers of salt seals at the surface. Methane then gets trapped under these seals, probably for a long period of time. Thus, when a 900-kg rover roams around with wheels equipped with grousers, it is most likely breaking the salt seals at the surface, releasing the trapped methane gas. Furthermore, Curiosity also drills into the rocks and surface, further weakening the seals, and most likely releasing more gas.

Further investigation is needed to gain a better understanding of the underlying mechanisms at work here, as this study does not fully elucidate the observed seasonal pattern. Nonetheless, it does offer novel insights into potential methane locations, under salt seals, thereby informing the design of future Mars missions.

How methane arrived in Gale Crater in the first place was not the scope of this study, so this remains unknown. On Earth, methane is mainly produced by microbial life, however, let us not get too carried away as geological processes on Mars, like serpentinization (involving olivine reacting with water), could also contribute to methane production.

Even with seven orbiters and three rovers actively studying the red planet, Mars continues to guard its many mysteries closely.

As always, onwards and upwards.


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