You must have heard about those gigantic oceans that exist on Earth: the Pacific, the Atlantic, and so on. But what if someone tells you there are oceans in our solar system which you have never seen? It turns out these mysterious bodies of water have been hidden under icy crusts of moons and dwarf planets.
Let us travel to the furthest, icy reaches of our solar system—to Eris and Makemake, two dwarf planets inside the Kuiper Belt that may be concealing gigantic oceans under their frozen surfaces. Scientists detected isotope ratios of frozen methane on these bodies, which can only give an indication of internal heating processes and very hard-to-deny evidence for liquid water existing beneath. We do see some pretty compelling signatures of hot times in cool places,” said Christopher Glein, a planetary geochemist from Southwest Research Institute in Texas.
No; Eris and Makemake aren’t the only ones. In fact, the moons of Jupiter and Saturn also with briny concealed oceans quite easily nourish life. Take Europa, for instance, which is Jupiter’s moon. For a long time, the grooved and fractured ice surface has remained of interest to scientists. When NASA’s Galileo spaceship discovered a magnetic field radiating from inside Europa, the only plausible explanation had to be one of an electrically conductive fluid, most likely of a liquid ocean beneath the ice.
Then there’s Saturn’s moon Enceladus. In 2004, geysers of ice were spotted bursting from its south pole by NASA’s Cassini spacecraft, suggesting that it might have an ocean salty with seawater beneath its surface. Cassini even grazed through the plumes, detecting organic and nitrogen-bearing molecules like methane that are fundamental for life as we know it. “That’s a no-brainer,” says planetary scientist Carly Howett.
Why do these hidden oceans matter? They could radically change our thinking about where life might exist in our universe. Steven Vance, an astrobiologist at NASA’s Jet Propulsion Lab, told me that these subsurface oceans could help “kick our quest into high gear about how easy, or troublesome, it is to get started with life throughout the cosmos.”
There’s more to learn! Other researchers have found what looks to be a global underground saltwater ocean in another Jupiter moon, Ganymede. A similar ocean could reside under the thick ice on Callisto, which also orbits Jupiter. Not to be left out of the party, scientists suspect that Titan, the largest moon around Saturn, features a salty subsurface ocean that may be sandwiched between layers of ice, or reach all the way down to the moon’s rocky interior. Imagine a moon containing lakes and rivers, but not of water—fluid hydrocarbons, such as methane and ethane!
It’s true that some of the newer missions, such as the Jupiter Icy Moons Explorer of the European Space Agency and NASA’s future Europa Clipper, will begin returning answers. One way or another, these missions will set a sharp, Detailed gaze on just such icy moons—one that might just nail down the presence and nature of those hidden oceans. As planetary scientist Francis Nimmo puts it, “I think it’s 99 percent sure there’s an ocean there” when talking of Europa.
What prevents these oceans from becoming solid blocs of ice in the cold vacuum of space? One such answer lies in tidal heating, where gravitational interactions like those between Jupiter and its moons create internal friction and heat. This is the case on Io, another of Jupiter’s moons, which is experiencing an extreme amount of volcanism resulting from such tidal forces. For Europa and Enceladus, it is tidal heating that appears to provide sufficient energy to keep their subsurface oceans liquid.
The other one is radiogenic heating: Radioactive decay in the core would release energy over billions of years, probably contributing to smaller bodies; this would keep oceans warm on larger moons like Ganymede, Callisto, and Titan. There is also chemical antifreeze that lowers the freezing point of water, making it possible for these oceans to remain liquid.
These hidden oceans evolve new mysteries as scientists make new theories when new data comes in. Scientists now discover that they may turn out to be more common than thought, expanding possible habitats for life beyond Earth. “Oceans under icy moons seem weird and improbable,” says Vance, yet here they are, definitely liquid.
Research into such hidden oceans promises the future right ahead of time: new life forms or even explaining life itself. With NASA’s Clipper mission to set off and confirm the existence of Europa’s ocean, we could stand at the threshold of revelations forever rearranging our place within the universe.
What better secrets does this icy moon hide? One thing, however, is certain: the enterprise to expose these unknown oceans is something to undertake.
