"If the biosignatures can't be detected in Earth samples ... we should not expect these instruments to be capable of detecting evidence of life from Mars' early history."
If you're hoping for NASA's most advanced Mars rovers to detect life on the Red Planet, you'll probably have to hold out until some samples make it back to Earth.
Take a new study, published in the journal Nature Communications, that had researchers investigate the capabilities of instruments used on Mars rovers by putting them through the wringer right here on Earth — with eyebrow-raising conclusions.
Keeping with the stony, arid environments of Mars, the researchers chose Red Stone, a dried-up river delta in the ancient Atacama Desert in Chile. Their initial analysis of Red Stone using some of the most advanced instruments available found signs — albeit scant — of microbial life, most of which they've novelly deemed "microbial dark matter." In other words, it's microbial life that's detectable but is so obscure and under-studied that it can't be positively identified.
Things really took a turn, however, when they examined the location using simulated instruments like those on Mars rovers like NASA's Curiosity and the upcoming ExoMars rover from the European Space Agency.
Even when using far more sensitive versions of those instruments, they were either "barely able to detect specific biogenic organic compounds" — in the case of Curiosity's SAM instrument — or didn't detect organics at all, writes Carol R. Stoker, a planetary scientist at NASA Ames Research Center who peer-reviewed the study, in an accompanying article in the journal Communications.
"This Red Stone sample analysis shows how critical it is to test instruments designed for life detection on other planets by using samples from relevant Earth analogs," Stoker wrote. "If the biosignatures can't be detected in Earth samples, where both current and ancient life is clearly documented, we should not expect these instruments to be capable of detecting evidence of life from Mars' early history."
The upside of this, though, is that a tentative absence of definitive biosignatures detectable by the rover's instruments doesn't mean there's no shot for life per se, just that rovers' onboard instruments can't necessarily detect it.
"We must be cautious about interpreting absence of strong evidence of life as evidence of its absence!" Stoker cautioned.
This makes returning Mars samples to Earth all the more crucial — and tantalizing. Think of it this way: if rovers' instruments are just scratching the surface now, just imagine what we could find when we get an extracted piece of Mars in a lab.
By NASA's current timeline, that could happen by 2033.
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