[Correction: jarosite has indeed been detected on Mars, this post has been updated to reflect that fact.]
Picture a hot volcanic spring.
Mineral-laden acidic water flows through sulfur-rich rocks. A foul odor hangs in the air. For us it's a nasty environment, best enjoyed through the lens of a tourist's camera. But for tough thermophilic microbes this is lovely, lovely stuff.
And that could be a problem in the search for signs of life on Mars.
This same kind of environment may have once existed on a young Mars, and could have served as an excellent incubator for living things. Indeed, some of the locales visited by NASA's small fleet of rovers over the past decade seem to be composed of the ancient remains of places that were once chemically harsh and wet, like terrestrial hot springs. Discoveries like these have directly influenced the strategies for exploration.
However, a new study suggests that a mineral - called jarosite, an iron sulfate - that would form readily in these potentially life-supporting conditions, might also confound the tests being performed by instruments like those on NASA's Curiosity rover to look for organic matter.
In a report in the journal Astrobiology, Lewis and colleagues describe the results of flash-heating jarosite mixed with organic matter, in the same way that Curiosity's onboard lab cooks samples. This procedure steps the temperature up to around 1000 Celsius while sniffing for interesting compounds as they're released. But the jarosite breaks down above 500 Celsius, producing sulfur dioxide and oxygen, and in these hot conditions the released oxygen reacts vigorously with any organics (carbon-containing materials that could be deposited by biology).
The upshot is that both the jarosite and the organics are likely to be destroyed, and the experimenter might not directly register their existence.
This worsens an already tricky situation. Naturally occurring perchlorates on Mars are known to complicate this kind of 'cooking' assay. The oxygen they produce has an equally destructive reaction with organics - effectively burning them up.
Jarosite contamination may or may not be recognizable, which is a big problem because it could be present in precisely the kind of environments you'd also want to look for organics in - fossil remains of hot springs.
It's quite a predicament, and
However, it's not yet known whether jarosite does indeed exist on the martian surface jarosite has indeed been identified on Mars, so this is a very real issue. To work around this problem it may be possible to deploy techniques that have been applied to perchlorate contamination, which involve studying the details of the carbon dioxide production in a sample that could indicate organic matter is getting destroyed. A similar approach might work if jarosite is present.
It seems that the natural environment on Mars and our experimental choices could be conspiring to obscure what's really lurking on the surface. It might be time for a radical rethink of how we go about analyzing martian soil.