智利阿塔卡马沙漠：火星生命的地球镜像
Beneath a salt crust in the hyperarid core of Chile’s Atacama Desert, where some weather stations have never recorded rain, a hidden microbial ecosystem clings to existence in a mineralogical purgatory. This landscape, more than any other terrestrial analogue, replicates the oxidised, polyextreme environment that likely dominated Mars during its transition from a wet to a dry planet several billion years ago. Geobiologists from institutions across the Americas and Europe now converge on these nitrate-rich clay pans, not merely to catalogue extremophiles, but to test the very operational definitions of biosignatures that will guide our next generation of Martian rovers. Their core question is disarmingly simple: if life hangs on here, where and how should we look for it elsewhere?
The endemic microorganisms employ a metabolic strategy known as deliquescence, in which certain hygroscopic salts absorb atmospheric water vapour and become transient, microscopic brine droplets — enough to trigger short bursts of DNA repair and cell division before the water evaporates again. One group, isolated from gypsum nodules in the Yungay area, survives on a diet of carbon monoxide and hydrogen gas, a biochemistry that would leave almost no organic trace in a planet’s geological record. These findings complicate the search for ancient life: a thriving subsurface biosphere on Mars might once have looked, to a surface-scanning spectrometer, like nothing more than sterile clay and perchlorate. In the Atacama, the frontier between alive and dead, between biotic and abiotic chemistry, is deliberately being made to collapse in laboratory settings so that a Martian signal, when it arrives, will not be dismissed as mere geological noise.
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