An international team has found that the water on Enceladus, one of Saturn’s moons, harbours phosphates, a key building block of life

The team led by the Freie Universität Berlin used data from NASA’s Cassini space mission to detect phosphates in particles ejected from the ice-covered global ocean of Saturn’s moon Enceladus.

Phosphorus, in the form of phosphates, is vital for all life on Earth.

It forms the backbone of DNA and is part of cell membranes and bones.

The new study is the first to report direct evidence of phosphorus on an extraterrestrial ocean world.

The team found that phosphate is present in Enceladus’ ocean at levels at least 100 times higher – and perhaps a thousand times higher – than in Earth’s oceans.

Third author Fabian Klenner, a University of Washington postdoctoral researcher in Earth and space sciences, said: “By determining such high phosphate concentrations readily available in Enceladus’ ocean, we have now satisfied what is generally considered one of the strictest requirements in establishing whether celestial bodies are habitable.”

While at Freie Universität Berlin, Klenner did experiments that revealed the high phosphate concentrations present in Enceladus’ ocean.



Ice grains from Enceladus


One of the most profound discoveries in planetary science over the past 25 years is that worlds with oceans beneath a surface layer of ice are common in our solar system.

These ice-covered celestial bodies include the icy moons of Jupiter and Saturn – including Ganymede, Titan and Enceladus – as well as even more distant celestial bodies like Pluto.

NASA’s Cassini mission explored Saturn, its rings and its moons from 2004 to 2017.

It first discovered that Enceladus harbours an ice-covered watery ocean, and analysed material that erupted through cracks in the region of the moon’s south pole.

The spacecraft was equipped with the Cosmic Dust Analyzer. which analysed individual ice grains emitted from Enceladus and sent those measurements back to Earth.

To determine the chemical composition of the grains, Klenner used a specialised setup in Berlin that mimicked the data generated by an ice grain hitting the instrument.

He tried different chemical compositions and concentrations for his samples to try to match the unknown signatures in the spacecraft’s observations.

Klenner said: “I prepared different phosphate solutions, and did the measurements, and we hit the bullseye.

“This was in perfect match with the data from space. This is the first finding of phosphorus on an extraterrestrial ocean world.”


Habitable zone


Planets with surface oceans, like Earth, must reside within a narrow range of distances from their host stars (in what is known as the ‘habitable zone’) to maintain temperatures at which water neither evaporates nor freezes.

Worlds with an interior ocean like Enceladus, however, can occur over a much wider range of distances, greatly expanding the number of habitable worlds likely to exist across the galaxy.

In previous studies, the team at the Freie Universität Berlin determined that Enceladus harbours a ‘soda ocean’, rich in dissolved carbonates, that also contains a vast variety of reactive and sometimes complex carbon-containing compounds.

The team also found indications of hydrothermal environments on the seafloor.

The new study now shows the unmistakable signatures of dissolved phosphates.

Lead author Frank Postberg at Freie Universität Berlin, said: “Previous geochemical models were divided on the question of whether Enceladus’ ocean contains significant quantities of phosphates at all.

“These measurements leave no doubt that substantial quantities of this essential substance are present in the ocean water.”

The research is published in Nature.

Image: An artist’s rendition of Saturn’s moon Enceladus depicts hydrothermal activity on the seafloor and cracks in the moon’s icy crust that allow material from the watery interior to be ejected into space. Those ejected particles, clues to the subsurface ocean, were analysed by instruments on board the Cassini space mission. New analysis finds evidence of phosphates, a key building block for life as we know it. Credit: NASA/ JPL-Caltech. Public Domain.

Research Aether / Space Uncovered