It was discovered that the carbon dioxide inside Enceladus is controlled by the chemistry of the seafloor, which is more complicated than imagined!

Scientists at the Southwest Research Institute have developed a new chemical model that reveals that carbon dioxide (CO2) in the interior of Saturn's moon Enceladus may be controlled by chemical reactions on its seafloor. Studies of gas plumes released through cracks in the moon's icy surface and frozen sea mist show that Enceladus' interior is much more complex than previously thought. "By understanding the composition of the plumes, we can understand what the ocean is like," said study author Dr. Christopher Glein of the Southwest Research Institute.

The new study, published in the journal Geophysical Research Letters, presents a new technique for analyzing plume composition to estimate dissolved carbon dioxide concentrations in the ocean, which enables modeling to explore deeper internal processes. Analysis of mass spectrometry data from NASA's Cassini spacecraft suggests that geochemical reactions between the moon's rocky core and liquid water from its subsurface ocean best explain the carbon dioxide abundance.

Combining this information with previously discovered silicon dioxide and molecular hydrogen (H2) reveals a more complex and geochemically diverse core. Based on the findings, Enceladus appears to demonstrate a large-scale carbon sequestration experiment. On Earth, climate scientists are exploring whether a similar process can be used to reduce industrial carbon dioxide emissions. Using two different data sets, scientists derived an interesting range of carbon dioxide concentrations that is very similar to the expected results of the dissolution and formation of certain mixtures of silicon- and carbon-containing minerals on the seafloor. Another phenomenon that contributes to this complexity is the possible presence of hydrothermal vents inside Enceladus.

On the planet's ocean floor, hydrothermal vents release hot, energy-rich, mineral-rich fluids that allow unique ecosystems to flourish, teeming with unusual organisms. "The dynamic interface of the complex core and seawater could generate energy sources that could support life," said Dr. Hunter Waite of the Sweet Institute, principal investigator of Cassini's Ion Neutral Mass Spectrometer (INMS). While no evidence of microbial life has been found in Enceladus' ocean, mounting evidence of chemical imbalances offers a tantalizing hint that habitable conditions could exist beneath the moon's icy crust.

The scientific community continues to harvest a lot of data from Cassini's close flyby of Enceladus before the end of the Cassini mission. A mass spectrometer detected H2 as the Cassini spacecraft passed through the plume. Another instrument earlier detected tiny grains of silica, two chemicals considered to be signatures of hydrothermal processes. The different sources of CO2, silica, and hydrogen observed indicate different environments, both mineralogically and thermally, in a heterogeneous rocky core. Researchers believe the inner core is composed of a carbonated upper layer and a serpentine interior.

Carbonates usually occur on Earth as sedimentary rocks, such as limestone, while serpentine minerals are formed from igneous seafloor rocks rich in magnesium and iron. Hydrothermal oxidation of reduced iron deep in the core produces H2, while hydrothermal activity intersecting quartz-bearing carbonate rocks produces silicon-rich fluids. Such rocks also have the potential to influence ocean CO2 chemistry through low-temperature reactions involving seafloor silicates and carbonates. The implications of heterogeneous core structures for possible life are intriguing, and this model could explain how processes of planetary differentiation and transformation produce the chemical (energy) gradients required for subsurface life.

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Boco Park | Research/Source: Southwest Research Institute

Reference journal Geophysical Research Letters

DOI: 10.1029/2019GL085885

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