What do you think of when you imagine a "water world" in space? Perhaps it's Miller's Planet from Interstellar with vast swaths of rolling tides, or Avatar: The Way of Water's lush marine ecosystem. However, recent missions have gathered evidence of water in our very own Solar System: Saturn's moon, Enceladus.
With a diameter of 500 km (310 mi), the unassuming icy Enceladus is often overshadowed by its bigger siblings like Titan or Europa (moon of Jupiter), the more well-known water worlds. However, astrobiologists have been interested in the small moon because of its unique characteristics. From 2005-2015, the NASA probe Cassini flew by Enceladus, discovering plumes that shot out from cracks in the moon's icy shell. (The Voyager flyby missed the plumes in 1981 due to a mechanical malfunction.)
The plumes are a great way to study Enceladus' contents because they're almost like Enceladus is coughing out its ocean through the cracks in its surface. The plumes provide important hints about what's hidden underneath the kilometers-thick ice shell. Instruments onboard Cassini analyzed the plumes' makeup as Cassini flew through them, finding gases such as oxygen, carbon dioxide, and ammonium.
In my research with UW graduate student Lucas Fifer, we compared the estimated concentration of these gases to known toxicity limits for various organisms on Earth. We found that there are overlaps between the possible concentration ranges of gases on Enceladus and ranges for organism survivability. This means Enceladus might be habitable by Earthlike life under the right conditions.
As you can see, though, the estimated ranges for the gases' concentrations on Enceladus is quite broad. Further observations and analysis of existing data need to be done to narrow down this range and understand Enceladus' habitability for Earth-like organisms.
Most recently, NASA JPL's analysis of the Cassini data found "strong confirmation of hydrogen cyanide," as reported by JPL on December 15. Although it's most commonly known as a highly lethal poison, it's also an important building block for amino acids necessary for the development of life.
Is Enceladus a promising haven for life, or should we look beyond our Solar System for better-suited worlds? Look forward to more astrobiology news in 2024, where humanity plans to venture to the moon, Mars, Europa, and beyond.
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Works Cited
Cofield, C. (2017, October 26). How Cassini Mission’s Twists and Turns Led to Discovery of Enceladus’ Plumes. Space.com; Space. https://www.space.com/38559-how-cassini-discovered-enceladus-plumes.html
https://www.jpl.nasa.gov. (2005, February 14). Enceladus First Flyby. NASA Jet Propulsion Laboratory (JPL). https://www.jpl.nasa.gov/images/pia06179-enceladus-first-flyby
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