There are potential geological processes that could also produce methane, but before even identifying the source of the gas on Mars, scientists attempted to solve another mystery.
Methane detections are inconsistent. Some instruments, such as NASA’s Curiosity rover, have repeatedly detected gas above the surface of Gale Crater. Others, like the ESA (European Space Agency) orbiter, found no trace of methane higher up in the Martian atmosphere.
On board the Curiosity rover is an instrument called a Tunable Laser Spectrometer (TLS) which has detected varying amounts of methane -om less than half a part per billion “equivalent to about a pinch of diluted salt in an Olympic-size swimming pool. To up to 20 parts per billion.
The problem cannot be a design issue or a malfunction. ESA’s ExoMars trace gas orbiter is “designed to be the gold standard for measuring methane and other gases across the planet,” NASA explained, and yet it did found no methane at all.
The TLS instrument is thus president, it has even been authorized for use in industrial systems and fighter planes to monitor gas levels.
“When the Trace Gas Orbiter arrived on board in 2016, I expected the orbiter team to report that there is a small amount of methane all over Mars,” said Chris Webster, who leads the TLS instrument for NASA.
“When the European team announced that they did not see methane, I was definitely shocked,” he added.
The TLS team checked to see if the rover itself released the gas somehow.
“We looked at the correlations with rover pointing, ground, rock crushing, wheel damage, and so on. I can’t stress enough how much effort the team put into looking at every little detail to make sure these measurements are correct. , and they are. “
At this point, John Moores, a scientist from York University in Toronto offered a counterintuitive solution.
“I took what some of my colleagues call a very Canadian take on this, in the sense that I asked the question, ‘What if Curiosity and Trace Gas Orbiter are both right? “” Moores said.
Working with the Curiosity team, Moores hypothesized that the gap between measurements boils down to the time they were taken.
The TLS, they realized, operates primarily at night when Curiosity’s other instruments are asleep. Since the Martian atmosphere is calm at night, any methane seeping from the ground collects near the surface.
The orbiter, however, depends on sunlight to locate traces of gas about 5 km from the surface of the planet. As the atmosphere is more active during the day, any methane present would have been diluted to undetectable levels.
Experiments quickly confirmed that this was the case, but another mystery lingered even beyond the origin of the methane: why was it disappearing?
Methane is a stable molecule. Even without a protective atmosphere, it should last 300 years on Mars before solar radiation tears it apart.
If it is constantly oozing out of all the craters on the planet – which researchers believe, because there is apparently nothing geologically unique about Gale Crater – then there should be enough in the atmosphere to that the orbiter can detect it.
Researchers are now experimenting to see if “dust-induced very low level electrical discharges in the Martian atmosphere could destroy methane, or if the abundant oxygen on the Martian surface rapidly destroys methane before it can reach the upper atmosphere ”.
“We need to determine if there is a faster-than-normal destruction mechanism to fully reconcile the rover and orbiter data sets,” Webster said.
After that, the team can try to figure out where the methane is coming from.