This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: We've been searching for life on Mars for a long time, but so far we've come up empty. The fundamental problem is a Catch-22 involving two of the key ingredients for life.
Life as we know it needs liquid water and reasonable temperatures, both of which are available on Mars, but hardly ever at the same time. But a new paper from lead author Anna Bognar and her team at ELTE Eötvös Loránd University and the Konkoly Observatory describes a way for life to access both requirements at the same time—by hiding away in salt crystals. To understand why, let's first look more closely at the Catch-22.
During the Martian night, the planet's air cools and its relative humidity climbs. Salts scattered across the surface can absorb some of that vapor through a process known as deliquescence. However, it is also much colder than any metabolizing organism could survive—dropping to -80℃, well out of range of life as we know it.
On the flip side, during the Martian day, temperatures warm to a much more reasonable 0℃, or even higher at some points near the equator. That's well within the operational range for known life forms—after all, Canadians deal with temperatures colder than that for almost half the year. However, during this warm period, the sun also burns off all the moisture, driving relative humidity down to near zero.
So while it's warm, all the water trapped overnight is suddenly gone. However, one feature of those massive temperature swings, which can reach 150℃ in a single day, can also be used to trap water. Materials contract and expand as they are cooled and warmed, creating a serious amount of mechanical stress on rocks undergoing that shift.
For example, according to the authors' models, halite (NaCl) salt crystals can contract by up to 1.6% between 150 K and 300 K, which can potentially open microscopic fractures and crevices. At that coldest point, in the dead of night, relative humidity also peaks, and the "hygroscopic" (i.e. water-absorbing) salt pulls moisture out of the air, forming microscopic brine. In the morning, the sun heats that same material, the crystal expands and it swells back to its original size, choking off the microfractures that formed during the night.
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