Reanalysis of icy rock grains from a ring of Saturn – fed by ice plumes from its moon Enceladus – has revealed the presence of phosphorus, the only key essential element for life that hadn’t already been spotted
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| Finding Phosphorus means Enceladus has now been shown to have all six ingredients essential for life (Credit: Cassini imaging Team/SSI/JPL/ESA/NASA) |
Saturn’s 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 unlikely to exist on icy ocean worlds.
The spacecraft Cassini collected icy rock grains with its Cosmic Dust Analyzer for 13 years from 1999 in Saturn’s E ring, which is thought to be fed from Enceladus’s plumes of water ice, which itself is fed from its oceans. But previous analysis of this material, in 2009, failed to turn up any phosphorus compounds.
Frank Postberg and his colleagues at the Free University of Berlin, have now reanalysed many of these grains with more advanced techniques than previously used and have identified phosphorus molecules. “Enceladus now satisfies what is generally considered one of the strictest requirements for habitability,” Postberg told the Europlanet Science Congress in Granada, Spain.
The original analysis could only look at the average spectra from the grains and didn’t 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 “unmistakably” have the fingerprint of phosphorus – as phosphates – 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’s ocean has relatively high levels of the element. “This is roughly 100 to 1000 times higher compared to the concentration here in our Earth ocean,” Postberg told the conference.
The phosphorus wasn’t 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’t identify these. However, said Postberg, “it doesn’t mean they’re not there”.
“It seems to be really compelling,” says Veronique Vuitton at Grenoble Alpes University in France. “It’s so exciting to find phosphorus, for all the obvious habitability reasons.”
“Enceladus 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,” said Pietro Matteoni at the Free University of Berlin.