Cassini’s Enceladus grains reveal salts sorted by slow freezing
Researchers analysed 961 Cassini measurements of salt-rich ice grains from Enceladus and found that different grains often contain different salts. In laboratory experiments, droplets around 200 micrometres across developed separated salt regions when they froze slowly; the researchers propose that larger frozen droplets then shattered inside the moon’s vents, producing the diverse grains Cassini detected. The study, published in Science Advances, says this process could concentrate compounds for future spacecraft to analyse, but does not show that life is present.
Bottom line — Future missions may need to analyse individual grains: rare compounds could be concentrated in only a small fraction of them.
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The Cassini data showed chloride and carbonate rarely appeared together in the same sodium-rich grain, according to the research team.
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In the experiments, droplets frozen at about 10 kelvins per minute or less showed salt separation; faster freezing kept the contents more evenly mixed.
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The team proposes that droplets freeze slowly deeper in Enceladus’s vents, then break apart after colliding with narrower icy channels nearer the surface.
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The researchers say freezing may also separate organics, but whether biological material behaves this way remains unproven.
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The team suggests that pockets of brine between ice crystals could concentrate salts and organic compounds, potentially bringing molecules together for prebiotic chemistry.