Search for methane on Mars: Observations,interpretation and future work

The detection of methane on Mars has been reported by three different teams in 2004. Two of them used ground-based high-resolution spectroscopy in the near infrared range. The third one used the Planetary Fourier Spectrometer aboard Mars Express. Among the data sets, two of them reported a mean CH₄ mixing ratio of 10 ppb. However, these are marginal detections, which should be considered as tentative. The third (ground-based) data set, unpublished so far, seems to show evidence for strong localized sources of CH₄, corresponding to mixing ratios as high as 250 ppb in some cases. However, the high values reported in 2003 were not confirmed by subsequent observations performed by the PFS instrument in 2004. In the absence of a refereed publication, it is difficult to judge if the high values are indeed correct. Assuming that they are, the lack of their confirmation by the PFS could have several explanations, including, among others, localized transient vents, or time variations in the methane destruction rate. A biogenic source was first suggested for the martian methane. However, later studies showed that an abiotic source such as hydrogeology can be just as effective. Further dedicated observations are obviously needed to firm up the detection and distribution of methane on Mars.