Could there be life on Saturn’s moon Enceladus? This icy world may be small (1/7 the size of our Moon), but it has a global ocean of water beneath its outer icy crust.
In fact, NASA’s Cassini spacecraft analyzed some of that water by flying through and sampling the moon’s water vapor columns. These plumes originate in the ocean and explode off the surface into space.
The results of the analysis suggested that the ocean could be suitable for some type of life, at least microbes. Last month, NASA announced a new study by researchers at the University of Washington that further supports this possibility.
It shows that the ocean is moderately alkaline (not too acidic) and may be even more habitable than previously thought.
Image Description: NASA’s Cassini spacecraft took this image of Enceladus on September 25, 2018. A new model of Enceladus’s ocean shows that it is moderately alkaline (not too acidic) and could be habitable for life. Image via NASA/ JPL-Caltech/ NASA Science.
The research team first published their peer-reviewed results in The Planetary Science Journal on August 11, 2022. NASA subsequently published the findings as a research highlight on November 30, 2022.
A new model of Enceladus’s ocean
Researchers created a new model of Enceladus’s ocean. This model helps predict what conditions are like and how similar or different they are to those of Earth’s oceans.
Thanks to Cassini, scientists already know that the ocean is quite salty, like the oceans of our planet. There is even evidence of hydrothermal vents on the ocean floor of Enceladus. On Earth, these vents provide heat and nutrients to a wide variety of organisms. The newspaper said:
Enceladus hosts an ocean beneath its icy crust from which spectacular columns of fissures emerge at the south pole. The plume’s composition was measured by the Cassini spacecraft and provides evidence of the ocean’s gas content, salinity, pH and potential for life.
When Cassini analyzed the water vapor plume, it discovered that the plumes contain water vapor, ice crystals, salts, ammonia, methane, and various organic molecules. This is not yet proof of life, but it is tempting.
The new model now updates the effects of salinity, pH and gas content on ocean habitability.
A moderately alkaline ocean
The results show that Enceladus’s ocean is probably even more habitable than initially thought. The model shows that the ocean is moderately alkaline with a pH (acidity) between 7.95 and 9.05. Earth’s oceans currently have an average pH of 8.1. Seven is considered a neutral pH. Everything below it is acidic and everything above it is basic (alkaline).
Additionally, the model suggests that there is enough carbon dioxide and hydrogen in the ocean to support hydrogenotrophic methanogens (microorganisms that consume carbon dioxide and hydrogen, releasing methane in the process).
The newspaper said:
With new estimates for the ocean gas content, we find an ocean pH of 7.95 – 9.05, encompassing the pH of the Earth’s ocean, high levels of NH4+ [ammonium] and inorganic carbon consistent with the accretion of Enceladus from of comet-like planetesimals. and an abundance of chemical energy for Encelade’s potential methanogens.
A cometary origin for Enceladus’s ocean?
The analysis also provides possible clues to the origin of Enceladus. The model predicts the amount of ammonia and inorganic carbon in the ocean. Those quantities, the model revealed, are consistent with the quantities that would come from comets. Researchers said this shows that Enceladus may have formed from comet-like materials.
These materials contained a high concentration of volatiles, chemical elements and chemical compounds that can easily vaporize. These may include nitrogen, carbon dioxide, ammonia, hydrogen, methane, sulfur dioxide, water and others. If the researchers are right, the ocean inside Enceladus is actually a remnant of those volatiles.
| Cutaway view of the interior of Enceladus showing the ice crust, global ocean, rocky core and water vapor plumes at the South Pole. Image via NASA/ JPL |
Not too salty, with a lot of methane.
If Enceladus’s ocean is not too acidic (moderately alkaline), it is a good sign that life may exist. Earlier this year, researchers at the Massachusetts Institute of Technology (MIT) also reported that the ocean is not too salty either. The ocean is salty, like Earth’s oceans, but too much salt can be harmful to living organisms.
Another study by a team of biologists in 2021 showed that Enceladus’s ocean also contains a lot of methane. Of course, scientists still don’t know whether methane is biological in origin or not, but it’s certainly a possibility. Could the new ocean model discussed here, which shows that there is enough carbon dioxide and hydrogen in the ocean to support hydrogenotrophic methanogens, perhaps be a clue?
Yet another study announced in 2020 indicated that Enceladus’ internal complexity is good for life. An even earlier study, from 2019, showed that Enceladus’s ocean is also the ideal age (one billion years) to support life. Very intriguing!
The Enceladus Orbilander mission proposed for the end of the next decade would search for life on Saturn’s icy moon.
Bottom line: NASA-supported researchers say Enceladus’s ocean is moderately alkaline like Earth’s oceans, raising the possibility that life exists in that dark abyss.
