At BBC Online David Whitehouse is reporting that the Mars Express PFS is going to report the detection of ammonia in the martian atmosphere at the COSPAR meeting next week. Obviously very exciting if the observations stand up; ammonia would be very unstable in the martian atmosphere and so would have to be constantly replenished, or if only present intermittently produced in contemporary fits and starts. It could clearly come from a biological source -- if Mars life is remotely like earth life it needs a nitrogen cycle. And the abiogenic sources of ammonia are probably scantier than those for methane: no serpentinisation, and no clathrates, I think (though ammonia can be mixed into water ice). So ammonia could be a strong signal of life.
But there are reasons to be a good bit more cautious about this detection than the methane detection (about which one should also be moderately cautious, though I must say I haven't been). The most important difference is that in the case of the methane, the news was particularly exciting because three different teams using a number of different instruments all seemed to see compatible results; here there is only one team reporting anything. Like the methane results, this ammonia result hasn't been published yet, and other scientists elsewhere haven't even seen the spectra at conferences yet. Indeed, as far as I know, the PFS team hasn't published results on anything as yet, and so there's no way for outside experts to assess the fine details of the ways in which they're analysing their data. As David notes in his piece, "[members of the PFS team] are still coming to terms with the complexities of the PFS as well as coping with some nagging power problems on Mars Express."
By a slightly freakish coincidence, I read the news while sitting next to Michael Mumma of NASA Goddard, one of the original methane observers (and thus, in some senses, a PFS competitor, though also a fellow striver after truth). Mumma -- who tried to detect ammonia in the martian atmosphere with earth-based instruments a few years ago, to no avail -- was clearly intrigued, but pointed out that if the ammonia detection was at ten microns (which the BBC report doesn't quite say, but which would be quite likely) then it would be very close to a quite striking carbon dioxide feature, and that if you were using a comparatively low resolution spectrometer such as PFS you'd want to be very careful indeed to make sure that the two bands weren't getting mixed up. Make of that what you will.
So if confirmed -- or simply published and scrutinised and found highly plausible -- this is extremely hot stuff: right now a very interesting thing to keep an eye on.
Incidentally, here in Iceland there is a delicacy called hakari made by burying sharks and leaving them to rot. Apparently it smells quite strongly of ammonia. Since Mars's ocean, if it has one, is undergound, it stands to reason that its sharks come ready-buried, and will thus be a potent ammonia source. Yet another way in which Mars is just Iceland writ large...