by John Timmer - Dec 17 2014, 11:26am MST On Earth, the majority of the methane that finds its way into the atmosphere is produced by microbes. Once in the atmosphere, the gas is broken down by a number of processes, so its continued presence there is a testimony to Earth's activity, both biological and geological. Mars' atmosphere breaks down methane as well, but there are also low levels of methane in its atmosphere. Although this methane could come from sources that don't involve biological or geological activity, some Earth-based observations had suggested that Mars had localized sources that create plumes of methane in its atmosphere. Those are tougher to explain, but the observations have been difficult to replicate. Now, the Curiosity rover has settled the issue, observing spikes in the atmosphere's methane concentration that seem to indicate a sporadic, local source. Various measurements of Mars' atmosphere have placed methane concentrations at roughly between five and 15 parts per billion. There are a number of potentially mundane sources for this methane, from the breakdown of organic chemicals delivered by small comets and asteroids to the reaction between some minerals and water. But those processes don't really explain the apparent observations of plumes of more concentrated methane in the atmosphere, which reach levels over three times the normal background before mixing into the atmosphere. The observations of these large-scale plumes, however, have been hard to replicate. That isn't entirely a surprise—as they're necessarily transient events—but it has left some questioning whether they actually existed. via Ars Technica.
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