Nasa's Curiosity rover has made an interesting nitrogen discovery on the surface of Mars.
Its big internal lab has detected nitric oxide (NO) - oxidised nitrogen - as it analysed dust and rock samples.
The compound was very likely released from the breakdown of nitrates during the heating of the powders.
If nitrates are the source, it would add to the evidence that the planet had the conditions necessary to sustain life in its distant past.
Nitrogen is essential for all known forms of life, but it needs to be in the right form to be useful.
On Earth, specialist soil microbes "fix" the not-so-useful nitrogen in the atmosphere into nitrate (NO3) - a nitrogen atom bound to three oxygen atoms - which can then be processed by other biological systems.
There is no evidence that the nitrates suggested in the Curiosity lab experiments were produced in this exact same way.
A more probable scenario, say rover scientists, is that the nitrates resulted from other conversion processes that involve lightning and meteorite strikes
The team saw the signs of the nitrates in scooped samples of surface dust and in samples drilled from mudstones.
These mudstones have already demonstrated that the ancient crater in which Curiosity sits had rivers and lakes, with water and a chemistry that would have been habitable.
Last week, rover scientists reported the possible detection of a fatty acid in the robot's drilled samples.
Fatty acids are key components of the cell membranes found in all life forms. But again - just as with the nitrates - there are non-biological routes to their production. Of itself, a detection proves nothing.
The nitric oxide result is reported by Jennifer Stern and colleagues in this week's edition of the journal Proceedings of the National Academy of Sciences.