Phosphates on Enceladus could mean sub-surface oceans teeming with aliens

Scientists analyzing data from the Cassini space probe have discovered that the sub-surface oceans of Saturn's moon Enceladus contain phosphates, a chemical necessary for the presence of life.

Phosphorus in phosphate form is essential in DNA, RNA, and cell membranes so researchers have long been curious about its presence on Enceladus since the discovery of sub-surface oceans and cryovolcanic plumes on the distant orb.

Launched in 1997, Cassini was designed to examine the systems of Saturn and Jupiter. The spacecraft – a joint project between NASA, ESA and the Italian Space Agency – made several passes of Enceladus between 2005 and 2015, as well as lurking in the planet's ring system.

A team led by Frank Postberg, professor of planetary science at the Free University of Berlin, analyzed data from Cassini's Cosmic Dust Analyzer (CDA), but it was a long wait to draw any conclusions.

"It has been on the NASA servers for everyone to look at for 15 years," Postberg told The Register. "This instrument delivered such a large amount of data that we were not able to analyze it all as the mission was active."

After publishing a limited analysis of the data in 2017, the team got funding from the European Research Council to analyze a much larger dataset.

"We didn't look specifically for phosphates. We just thought, let's look at a much larger dataset and much larger compositions of individualized grains. After more than three years, I found these nine ice grains which have this highly significant signature of phosphates," he said.

Life requires carbon, hydrogen, nitrogen, oxygen, phosphorus and sulphur, Postberg explained. "From these six, phosphorus was the only one missing in the Cassini data."

Data from the E-ring of Saturn was chosen because it is formed by ice grains escaping Enceladus's cryovolcanic plume and provides better statistics compared with data from the rare occasions when Cassini traversed the plume itself. The team also conducted lab experiments to replicate the space data to understand and confirm what the data from the probe means, Postberg said.

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The professor said the team's work had already attracted considerable attention, and an article accompanying its paper in Nature this week shows why.

"The presence of phosphorus compounds in water is crucial for biological productivity on Earth, and is, therefore, a key factor when assessing whether distant worlds have the potential to support life… The new results also imply that aqueous phosphates could be abundant on other ice-covered bodies in the outer Solar System thought to have subsurface oceans, increasing the prospects of their habitability," Mikhail Zolotov, professor of planetary geochemistry at Arizona State University, said in the article.

But getting evidence from other moons with oceans will take time.

ESA's Juice probe began its eight-year mission to Jupiter in April, while NASA is set to launch the Europa Clipper to the same planet system in October next year and expects it to arrive in 2030.

"We will find out more in at least seven years. If you work in the outer solar system, you need patience," Postberg said. ®