Enceladus is one of Saturn’s 83 confirmed moons, discovered in 1789 by William Herschel. This icy moon is only 310 miles in diameter, making it one of the smaller moons of Saturn, yet it harbors one of the most promising environments in our solar system for the potential discovery of extraterrestrial life.
Key Features of Enceladus
Enceladus has several unique features that make it a prime target in the search for life beyond Earth:
Global Ocean: Enceladus has a global subsurface ocean 6-10 kilometers deep located beneath an ice shell 30-40 kilometers thick. Cassini gravity measurements confirmed the existence of this vast ocean in 2014.
Hydrothermal Vents: There is strong evidence that Enceladus’ seafloor features active hydrothermal vents, which could provide energy and nutrients to fuel microbial life.
Organic Compounds: Cassini detected organic compounds like methane, propane, acetylene and formaldehyde in the plumes erupting from Enceladus’ south pole. Organic compounds are chemical building blocks of life.
Phosphorus: In 2022, scientists found evidence of phosphorus in Enceladus’ ocean, an essential ingredient for life on Earth. This was the first detection of phosphorus on an extraterrestrial ocean world.
The Plumes of Enceladus
The most visually striking feature of Enceladus is the impressive plumes that erupt from its south polar region. These plumes were first observed by Cassini in 2005. The plumes blast water vapor, ice particles, salts, and organic molecules from Enceladus’ subsurface ocean out into space.
Cassini flew through these plumes multiple times, collecting and analyzing samples. These flythroughs revealed that the plume material originates from a global saltwater ocean with conditions that could be hospitable to life. The plumes provide a way to directly sample the composition of Enceladus’ potentially habitable ocean without having to land on or drill through the moon’s thick icy crust.
How Enceladus’ Ocean Formed
Enceladus’ ocean likely formed through tidal heating, which is the friction generated from gravitational interactions with Saturn. The gravitational pull of massive Saturn flexes and stretches the smaller Enceladus, generating internal friction and heat within the moon’s interior. This allows Enceladus to maintain liquid water beneath its icy crust despite being far from the Sun.
Tidal heating keeps Enceladus’ ocean from freezing solid and creates optimal conditions for hydrothermal activity on the seafloor. The chemical energy from hydrothermal vents could help sustain basic forms of life, just as such vents do on Earth’s ocean floor. Enceladus’ ocean world may have existed for billions of years, allowing ample time for life to emerge and evolve.
How Might Life Survive on Enceladus?
If life does exist in Enceladus’ dark ocean depths, it would likely be in the form of microbes living around hydrothermal vents. On Earth, such vent microbes derive energy from chemical reactions using compounds like hydrogen and methane. They do not need sunlight.
Some scientists think life may have originated around hydrothermal systems on early Earth. If a similar process occurred on Enceladus billions of years ago, life conceivably could have had time to take hold and thrive in the moon’s warm ocean, hidden beneath the icy crust.
Enceladus has many ingredients thought to be essential for life as we know it: liquid water, organic molecules, nitrogen compounds, salts, phosphorus, and an energy source. Its ocean contains more sodium chloride salt than Earth’s oceans. The salinity provides stability, lowering the freezing point of water. In addition, the ocean may contain ammonia, which could serve as another antifreeze compound.
How Could We Detect Life on Enceladus?
A future spacecraft equipped with more advanced instruments than Cassini could be sent to fly through Enceladus’ plumes and analyze the materials spewed from the moon’s ocean. Scientists could search for chemical biosignatures – compounds or mixtures of compounds that could be signs of life, such as certain complex organic molecules, lipids, or amino acids that may make up alien cell membranes or proteins.
Another option would be to directly sample the ocean by landing a probe on Enceladus capable of drilling through the icy crust to analyze the water below. However, this would be an extremely challenging endeavor requiring advanced technologies.
Why Enceladus is a High Priority Target
Enceladus has rapidly become one of the most promising ocean worlds in our solar system and a top target in the search for life due to its global subsurface sea, hydrothermal activity, organic-rich plumes, and presence of phosphorus. The ingredients and energy sources thought to be required for life are all present in its ocean.
Enceladus offers easier access than Jupiter’s moon Europa to directly sample an extraterrestrial ocean. Europa’s ocean is buried beneath a thick crust of ice estimated to be 15-25 kilometers deep, whereas Enceladus’ south polar fractures provide a way to sample its ocean through its plumes.
The relative ease of accessing Enceladus’ plumes and the tantalizing evidence for hydrothermal vents make it a compelling target. Its hidden ocean could be the best place beyond Earth to search for signs of life in our solar system.
Summary
Saturn’s small, icy moon Enceladus conceals a global subsurface ocean that may possess the essential ingredients and energy sources needed for life. Plumes erupting from Enceladus’ south pole allow us to directly sample the chemistry of this ocean without having to drill through miles of ice.
Evidence suggests Enceladus’ seafloor features hydrothermal vents, a promising environment that could support basic forms of life like microbes. The detection of phosphorus, a critical ingredient for life, in the ocean further bolsters the case for Enceladus as a potentially habitable world.
NASA and other space agencies have made exploring ocean worlds like Enceladus a top priority. Future missions could conclusively determine if Earth is the only place in our solar system where life exists, or if the dark ocean depths of Enceladus also harbor an alien biosphere waiting to be discovered.
