NASA’s Cassini captured a mosaic of the surface of Enceladus on Oct. 9, 2008. (NASA/JPL/Space Science Institute) | SkyNews
NASA’s Cassini captured a mosaic of the surface of Enceladus on Oct. 9, 2008. (NASA/JPL/Space Science Institute)

Subsurface ocean could be similar to Earth’s

Researchers believe Enceladus is made from comet-like building blocks and the gas-rich ocean is a remnant of these materials.

Scientists studying Saturn’s moon Enceladus believe the conditions of the icy world’s subsurface ocean could be closer to Earth’s oceans than previously thought.

The data comes from NASA’s Cassini spacecraft, which flew through plumes of water vapour that were spewed hundreds of kilometres into space. The spacecraft then transmitted data on what the plumes were made of and estimates on the ocean’s salinity, pH, and gas content.

“The results of the new model indicate that the ocean is moderately alkaline with a pH between 7.95 and 9.05. This prediction is closer to Earth-like conditions for pH than previous estimates,” wrote Aaron Gronstal on NASA’s astrobiology blog.

The authors of the study at the Planetary Science Journal also noted that the ocean has the concentrations of carbon dioxide and hydrogen needed to support hydrogenotrophic methanogens. These are microorganisms that release methane after consuming carbon dioxide and hydrogen.

The ocean of Enceladus could also be rich in gas, with high amounts of ammonium ions. Researchers believe Enceladus is made from comet-like building blocks and the gas-rich ocean is a remnant of these materials. A model based on Cassini’s data predicts bulk ammonia and inorganic compounds are consistent with the remains of comets.

There are caveats in the study itself, though. The conditions of the oceans on Earth and Enceladus are different. The ones on Earth’s surface are exposed to winds, while Enceladus’ ocean boils. 

According to the paper, any discussion of life on Enceladus is “decidedly biased” toward terrestrial “life as we know it” examples, and “an Earth-like pH may not necessarily be advantageous for extraterrestrial biology.”

Enceladus’ underground ocean has only been glimpsed through huge geysers of water sprayed from deep vents in the moon’s icy surface. Cassini flew through these geysers on several occasions before its mission ended in 2017.

It is not known when scientists will return to Enceladus. A proposed mission called the Enceladus Orbilander would send a spacecraft to orbit the moon for 18 months sampling the plumes. It would then land on the moon for a two-year mission.

The concept is estimated to cost more than US$4.9 billion and would launch in the 2030s. The spacecraft would not arrive at Enceladus until the 2050s.

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