Added 1 new A* page:There was a lot of news last week about potential habitable (or previously habitable) water worlds in our solar system; I *think* this was spurred by NASA finally concluding that the Cassini probe did detect molecular hydrogen in a plume of ice it flew through from Saturn's moon Enceladus in late 2015—that's what the BBC's article is about, anyway.
On Earth, hydrogen molecules can get into seawater like so: "At the mid-ocean ridges on our planet, seawater is drawn through, and reacts with, hot upwelling rocks that are rich in iron and magnesium. As the minerals in these rocks incorporate H2O molecules into their crystal structure, they release hydrogen..." So, detecting hydrogen in the geysers thought to be spewing upward from Enceladus' subsurface oceans *could* mean that those oceans have hot underwater vent areas that could support life; at any rate, the food source those vent areas have is definitely present in Enceladus: on Earth, microorganisms classed as "methanogens" use released hydrogen as food—they "make methane as they react the hydrogen with carbon dioxide."
The article mentions that to detect the presence of actual tiny life forms, or their unmistakable traces, in the ice plumes shooting out of Enceladus, you would need a different kind of spectrometer than Cassini is equipped with, and that "a proposal is being put together to fly them in 2026."
It ends with an informative biochemistry quote from Cassini scientist Dr. Hunter Waite: "For life, you need liquid water, organics, and the CHNOPS elements (carbon, hydrogen, nitrogen, oxygen, phosphorus, sulphur). OK, we haven't yet measured phosphorus and sulphur at Enceladus. But you also need some kind of metabolic energy source, and the new Cassini results are an important contribution in that regard."
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