杏吧原创

Saturn鈥檚 moon Enceladus is producing phosphorus, meaning that this icy moon holds all the essential building blocks for life as we know it.

Every life form on Earth contains six key elements: carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur. The known existence of these, bar phosphorus, on Enceladus, combined with a liquid ocean and a warm core, had already made the moon one of the most likely places for life elsewhere in the solar system, if it exists. But the lack of phosphorus was thought by some to make life ocean worlds.

The spacecraft Cassini collected icy rock grains with its Cosmic Dust Analyzer for 13 years from 1999 in Saturn鈥檚 E ring, which is thought to be fed from Enceladus鈥檚 plumes of water ice, which itself is fed from its oceans. But

Now, at the Free University of Berlin, Germany, and his colleagues have reanalysed many of these grains with more advanced techniques than previously used and have identified phosphorus molecules. 鈥淓nceladus now satisfies what is generally considered one of the strictest requirements for habitability,鈥� Postberg told the Europlanet Science Congress in Granada, Spain, on 20 September.

The original analyses could only look at the average spectra from the grains and didn鈥檛 have good spectra of known compounds from lab work that they could compare their findings against to work out what was in the Cassini grains.

But Postberg and his team have now analysed many more grains individually and compared their spectra against high-resolution ones that have been captured by other research groups in the decade since the first analysis.

Out of the roughly 1000 grains they analysed, nine 鈥渦nmistakably鈥� have the fingerprint of phosphorus 鈥� as phosphates 鈥� in the form of various salts it forms with sodium, hydrogen and oxygen.

Based on the levels of phosphorus found in the grains, the researchers predict that Enceladus鈥檚 ocean has relatively high levels of the element. 鈥淭his is roughly 100 to 1000 times higher compared to the concentration here in our Earth ocean,鈥� Postberg told the conference.

The phosphorus wasn鈥檛 seen in organic carbon-containing molecules, though. Organic phosphates would be even more beneficial for life, but the resolution of the spectrometer that the researchers used meant they couldn鈥檛 identify these. However, said Postberg, 鈥渋t doesn鈥檛 mean they鈥檙e not there鈥�.

鈥淚t seems to be really compelling,鈥� says at Grenoble Alpes University in France. 鈥淚t鈥檚 so exciting to find phosphorus, for all the obvious habitability reasons.鈥�

鈥淓nceladus was already one of the most likely bodies in the solar system with a high habitability potential and this makes it an even stronger case,鈥� says at the Free University of Berlin, who wasn鈥檛 involved with the research.

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