The controversy over whether or not there is methane on Mars and what it might mean looks set to rage on after the latest readings found next to no evidence of the gas.
The European Space Agency’s ExoMars Trace Gas Orbiter reported its first results in papers in Nature, including the strange absence of methane compared to previous findings.
“We have beautiful, high-accuracy data tracing signals of water within the range of where we would expect to see methane, but yet we can only report a modest upper limit that suggests a global absence of methane,” said ACS principal investigator Oleg Korablev from the Space Research Institute, Russian Academy of Sciences, Moscow, in a statement.
Methane has been detected on Mars by a number of missions, including ESA’s Mars Express orbiter, NASA’s Curiosity rover and numerous Earth-based telescopes.
But the amount they’ve detected has varied wildly and the latest readings look set to add to the debate. Trace gases of any kind take up less than 1% of an atmosphere by volume and are usually measured in parts per billion by volume (ppbv). On Earth, methane measures about 1800 ppbv, so for every billion molecules in the atmosphere, 1800 of them are methane.
Mars Express clocked one of the first measurements of methane from Martian orbit in 2014 as just 10 ppbv. Since then, Earth-based telescopes have failed to detect any methane at all and reported up to 45 ppbv. The Curiosity rover, on the surface since 2012, has picked up background levels of between 0.2 and 0.7 ppbv that appear to vary by the seasons. Every so often, it also picks up a spike in the readings.
The new results from TGO, which is the most detailed planet-wide analysis yet, found an upper limit of 0.05 ppbv, so around 10 to 100 times less than anyone else. That means either all the other readings were wrong or the methane has mysteriously vanished.
“The TGO’s high-precision measurements seem to be at odds with previous detections; to reconcile the various datasets and match the fast transition from previously reported plumes to the apparently very low background levels, we need to find a method that efficiently destroys methane close to the surface of the planet,” said Korablev.
Methane on Mars is of particular interest to scientists because on Earth, most of the methane in the atmosphere comes from biological processes. The presence of methane in any atmosphere could be a solid indicator of signs of life.
“Just as the question of the presence of methane and where it might be coming from has caused so much debate, so the issue of where it is going, and how quickly it can disappear, is equally interesting,” said Håkan Svedhem, ESA’s TGO project scientist.
“We don’t have all the pieces of the puzzle or see the full picture yet, but that is why we are there with TGO, making a detailed analysis of the atmosphere with the best instruments we have, to better understand how active this planet is – whether geologically or biologically.”