Subsurface Ocean of Enceladus is Rich in Phosphorus, Suggests Study

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Subsurface Ocean of Enceladus is Rich in Phosphorus, Suggests Study


Enceladus is one of the prime targets in the search for life in our Solar System. Observations made by NASA’s Cassini spacecraft show that this small Saturnian moon has an ice-covered water ocean that erupts into space, forming a plume that contains almost all of the basic requirements of terrestrial life. In new research, scientists from the United States, Australia, China and Germany performed geochemical modeling to predict how much the bioessential element phosphorus could be present in the Enceladus ocean.

Phosphorus in the form of orthophosphate (e.g., HPO4-2) is likely abundant in the subsurface ocean of Saturn’s moon Enceladus; a soda or alkaline ocean (containing NaHCO3 and/or Na2CO3) inside of Enceladus interacts geochemically with a rocky core; modeling indicates that this interaction promotes the dissolution of phosphate minerals, making orthophosphate readily available to possible life in the ocean; because phosphorus is an essential ingredient for life, this finding bolsters mounting evidence for habitability within this small Saturnian moon. Image credit: Southwest Research Institute.

The search for habitable worlds is usually guided by the presence of liquid water.

Apart from Earth, water oceans also exist in the subsurface regions of some icy bodies — e.g., Enceladus, Europa, and Titan — in the outer Solar System.

The evidence for an ocean is strongest at Enceladus, where a water-rich plume erupts from a subsurface ocean.

“What we have learned is that the plume contains almost all the basic requirements of life as we know it,” said Dr. Christopher Glein, lead scientist at the Southwest Research Institute.

“While the bioessential element phosphorus has yet to be identified directly, our team discovered evidence for its availability in the ocean beneath the moon’s icy crust.”

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

This element is essential for the creation of DNA and RNA, energy-carrying molecules, cell membranes, bones and teeth in people and animals, and even the sea’s microbiome of plankton.

In their research, Dr. Glein and his colleagues performed thermodynamic and kinetic modeling that simulates the geochemistry of phosphorus based on insights from Cassini about the ocean-seafloor system on Enceladus.

They developed the most detailed geochemical model to date of how seafloor minerals dissolve into Enceladus’ ocean and predicted that phosphate minerals would be unusually soluble there.

“The underlying geochemistry has an elegant simplicity that makes the presence of dissolved phosphorus inevitable, reaching levels close to or even higher than those in modern Earth seawater,” Dr. Glein said.

“What this means for astrobiology is that we can be more confident than before that the ocean of Enceladus is habitable.”

‘The next step is clear: we need to get back to Enceladus to see if a habitable ocean is actually inhabited.”

The study was published in the Proceedings of the National Academy of Sciences.

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Jihua Hao et al. 2022. Abundant phosphorus expected for possible life in Enceladus’s ocean. PNAS 119 (39): e2201388119; doi: 10.1073/pnas.2201388119

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