A brief spike in methane levels in the Martian atmosphere has once again been detected, hinting at a localized source that may be biological in nature.
On Earth, more than 90 percent of methane in the atmosphere is produced by biological sources - life. Mars normally has low background levels of methane in its atmosphere, which can be explained by the Sun's rays slowly degrading organic material that may have been deposited by meteorites, according to NASA scientists. But observations of the red planet over the years have detected unusual spikes in methane levels, the most impressive of which happened shortly after Thanksgiving 2013.
In a report to be published in this week's issue of Science, the event is described as having lasted for 60 Martian days and is said to have seen methane levels increase tenfold. Methane levels have remained at background levels ever since.
"What is interesting is that these spikes of methane are coming and going. They are transient," said Dr Paul Mahaffy at Nasa. "At the moment we can't really tell anything, but these burps are intriguing. We have to keep an open mind.
"We don't want to eliminate anything, and potentially it could indicate life or evidence of ancient methane trapped which could show ancient life.
"But it's interesting to think about why it comes and goes. It seems to be suggestive of a localized source."
Non-biological sources of methane include meteorites, volcanic deposits trapped in ice, and gaseous methane bound in soil, but scientists don't believe any of these could have caused the observed 2013 spike. While they aren't saying anything conclusive, the formation of methane by microbial life remains a possible explanation.
The readings were taken by the Curiosity rover in Mars' Gale Crater. The rover has been exploring the 96 mile wide crater since 2012, and NASA believes that with more readings, it can analyze isotope levels and prove whether the methane emissions are biological in origin.
Curiosity is presently making its way up Mount Sharp in Gale Crater, where it has been uncovering evidence of Martian features formed by water and lava.