But under the cold shell is a soft underground ocean, which is famous for its huge water column ejected from the ice. Cassini spacecraft dived into these plumes while exploring Saturn and its moons, and detected an unusually large number of molecules, such as methane, dihydrogen and carbon dioxide.
This shows that there are hydrothermal vents on the seabed where the ocean meets Enceladus rock core. This dynamic environment is the main habitat of microorganisms, where they consume dihydrogen and carbon dioxide and release methane.
So does this mean that there are alien microbes living around the hydrothermal vent of Enceladus? Or can the detected molecules be explained by these geochemical processes alone? To find out, the researchers run the model to find out which situation best fits the observation.
The team simulated different possible environmental conditions on Enceladus and introduced hypothetical methane-producing microorganisms based on known strains on earth. They checked whether the hydrothermal cycle can provide enough dihydrogen for microorganisms to "eat", whether the temperature is suitable for them, and more importantly, what impact microorganisms will have on their surroundings-especially the concentration in the plume. Then, the results of these models are compared with those actually detected by Cassini in plumes.
"In short, if methane generation really happens at the bottom of Enceladus, we can not only evaluate whether Cassini's observation results are suitable for life, but also quantitatively predict the observation results," said Régis Ferrière, the main author of this research paper.
Sure enough, the conditions there seem to be conducive to this life form-but more interestingly, there is no known hydrothermal chemical that can explain the methane level detected in the plume. Only when biological sources are added to the model will the level be consistent with the observed results.
"Obviously, we can't conclude that there is life in the ocean of Enceladus," Ferrier said. "On the contrary, we want to know how likely it is that the hydrothermal vents of Enceladus are suitable for terrestrial microorganisms to survive. According to our model, Cassini's data tells us that it is very possible. Biogenic methane production seems to be consistent with the data. "
Of course, this may not be life. But if not, it must be some other natural phenomenon that we can't see on earth. One solution proposed by the research team is that the original organic matter in Enceladus core can be decomposed into methane, dihydrogen and carbon dioxide through hydrothermal activity. But this possibility depends on how Enceladus was formed.