Levels of methane on Mars have dropped following a spike detected by Nasa’s Curiosity Rover last week which fuelled discussions about the possibility of life.
The American space agency’s rover spotted its highest amount of the gas yet, though scientists cautioned that methane can also be created through interactions between rocks and water.
Planned operations were scrapped this weekend in favour of taking a second reading, showing that the amount of methane had dropped to background levels of one part per billion units by volume (ppbv), down from the 21 ppbv measured on Wednesday.
Nasa has therefore referred to it as a transient methane plume.
This change matches up with previous highs and lows picked up by Curiosity’s Sample Analysis at Mars (SAM), an instrument tasked with analysing gases, although last week’s measurement is the highest concentration the mission has recorded since landing on the planet in August 2012.
“We did make the run again, the data just came back and in fact the methane plume went away,” Paul Mahaffy, principal investigator for SAM, said at a Nasa town hall event at the Astrobiology Science Conference on Monday.
Curiosity is not fitted with equipment to figure out the source of the methane, making it impossible to tell whether it is biological or geological.
Methane is destroyed by solar radiation within several hundred years when it enters the atmosphere, so it must have been released quite recently.
Despite this, there remains the possibility that the gas could have been trapped underground for millions or billions of years, and only just been released.
“The methane mystery continues,” said Ashwin Vasavada, Curiosity’s project scientist at Nasa’s Jet Propulsion Laboratory.
“We’re more motivated than ever to keep measuring and put our brains together to figure out how methane behaves in the Martian atmosphere.”
Dr Mahaffy said they would continue to work with other missions on Mars, such as the European Space Agency’s Mars Express spacecraft and the Trace Gas Orbiter, to uncover any signs of life on the Red Planet.