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In its second significant science release yesterday (the first relating to the discovery of organics), the Curiosity science team revealed that they have found over almost three Martian years the amount of methane in the atmosphere appears to fluctuate seasonally. The graph on the right illustrates this change.
[The data] show methane rises from just above 0.2ppb in the northern hemisphere winter to a fraction over 0.6ppb in the summer. The team’s best explanation is that methane is seeping up from underground, perhaps from stored ices, and is then being released when surface soils are warmed.
The team cannot positively identify the origin of the methane, but the researchers think they can close down one particular mechanism for its production. This involves sunlight breaking up carbon-rich (organic) molecules that have fallen to the planet’s surface in meteorites.
The variation in ultraviolet light over the course of the seasons is not big enough to drive the scale of the change seen in the methane concentration, says Dr Webster. “We know the intensity of the Sun and this mechanism should produce only a 20% increase in methane during the summer, but we’re seeing it increase by a factor of three,” he explained.
The change could be caused by either a chemical or a biological process. At this time there is no way to determine which.