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Enceladus, Saturn’s moon with a hidden ocean
Highlights
- Saturn's moon Enceladus likely hosts a global ocean of liquid water under its icy surface.
- NASA’s Cassini spacecraft flew through geysers spewing from the moon's south pole, finding evidence of organic compounds.
- It's possible that this ocean world could be a habitable environment for alien life.
What's Enceladus like?
Though tiger stripes streak across the surface of Enceladus and a planetary ring orbits around it, perhaps the most intriguing thing about this icy moon of Saturn is what lies beneath: a subsurface ocean about 2% of the size of all of Earth's oceans. That may sound small, but given the entire moon's surface covers about as much area as France, it's not a drop in the bucket.
Enceladus is too cold to host liquid water on its surface, and it lacks a thick atmosphere. Underneath its ice shell, its ocean stays liquid because it's salty (which lowers the melting point of ice) and because it's heated, possibly by the moon’s insides being stretched and compressed by the gravitational pull of its host planet (caled "tidal heating").
Compared to Europa, the icy moon of Jupiter also famous for its probably subsurface ocean, Enceladus is much smaller. But what really sets Enceladus apart are the dozens of geysers around its south pole, which launch plumes of gas and ice grains away from the moon. These plumes make it much easier to investigate the interior of Enceladus. Instead of sending a probe to somehow drill into its icy shell, we can just send one to fly through a plume and get a sense of what’s inside.
Why explore Enceladus?
Liquid water is one of the main requirements for life as we know it. Not only does Enceladus likely host an ocean, it may also host the other chemical ingredients required for Earth-like life to thrive.
At the beginning of the 1980s, the twin Voyager spacecraft became the first missions to study Saturn's moon Enceladus up close. They found a surface without many craters and made other geologic discoveries. Then, in 2005, the Cassini mission performed the first of several flybys of Enceladus. These flybys unveiled the first major signs of Enceladus' ocean as well as the plumes of ice particles coming from its south polar region.
Cassini, which was operated by NASA and the Jet Propulsion Laboratory, flew through the plumes of Enceladus in 2015. The spacecraft found evidence of interaction between the rocky seafloor and liquid ocean, as well as hints of hydrothermal vents and organic molecules using its spectrometer. On Earth, hydrothermal vents are known as places where life can thrive without sunlight — some scientists think they may even be where life first originated on our planet — so their potential discovery on Enceladus is especially promising. For all these reasons, Enceladus is considered by many scientists to be essentially habitable.
Cassini didn’t detect life on Enceladus. But it did suggest the moon might have the right components for life: water, energy sources, and organic materials. All of this is a great reason to someday go back to Enceladus and take a closer look.
Enceladus Facts
Surface temperature: -201 degrees Celsius (-330 degrees Fahrenheit)
Average distance from Sun: 9.5 AU
Diameter: 504 kilometers (313 miles)
Volume: 67.1 million cubic kilometers (roughly 16 million cubic miles)
Gravity: 0.113 m/s²
Solar day: 32.9 hours
Solar year: N/A
Atmosphere: Mostly water vapor; small amounts of nitrogen, carbon dioxide and methane