Back in 2009, some Earth-based observations found what could potentially cause a complete reworking of our understanding of Mars: seasonal plumes of methane billowing into the red planet's atmosphere. On Earth, methane is most frequently associated with either biological or geological activity, and we generally don't think Mars has much of either. But the Martian summers appeared to cause a large outpouring of the gas from a limited area on Mars. The gas was not present in the winter.

It's very difficult to account for a source of methane this large based on what we know of Mars. The environment there is extremely inhospitable to life, even during the Martian summer. And all our imaging of the surface indicates that major geological activity ended long ago, leaving the planet's surface to be shaped by a variety of weathering processes.

Later analyses have cast doubt on the original findings, but we should be able to get a definitive answer as to whether Mars has methane later today. That's because NASA will be announcing the results of atmospheric sampling performed by the Curiosity rover.

If the methane plumes were unexpected at the time, they have only become more so since. Follow-up observations have failed to detect anything, but a study of a meteorite indicated that it is possible to generate low levels of methane simply by exposing carbon-rich meteorites to UV light.

Meanwhile, other researchers have calculated that there are a few problems with the initial observations. For one, they estimate that the presence of the levels of methane seen in the earlier report would react with enough oxygen in the atmosphere to leave Mars' air oxygen-free within 10,000 years. They also suggest that Mars' orbital motion may have created a Doppler shift that made Martian methane difficult to distinguish from Earth's at the time when the positive signals were seen.

The simplest way around all this is to just go and sample Mars' atmosphere. Conveniently, the Curiosity rover has the equipment to do just that. According to Nature News, the rover's Tunable Laser Spectrometer is designed to sample the atmosphere and provide a detailed chemical inventory. This reading will be precise enough to identify the isotopes of carbon present in the gasses it detects, which may also help provide some hint about the source of any methane it detects.

We'll be listening in on the press call, so check in later today for any updates.