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A Moon with an Ocean

There’s an ocean under the surface of Mimas, one of Saturn’s moons. What does this mean for life beyond Earth?
A moon with many craters

NASA/JPL/Space Science Institute

Mimas, one of Saturn’s moons, is known for the large crater that makes it look like the Death Star from the Star Wars movies.

Could life beyond Earth exist in our own solar system?

Scientists have discovered that there’s an ocean hidden beneath the icy surface of Mimas, one of Saturn’s moons. The finding suggests there may be more liquid water—which is needed to support life as we know it—beyond Earth than scientists had previously thought.

Until recently, Mimas’s biggest claim to fame may have been that a large crater on its surface makes it look like the Death Star from the Star Wars movies. Other than that, astronomers thought it was just a ball of ice. But when scientists studied images and data collected by a spacecraft called Cassini, they learned that Mimas’s orbit around Saturn is affected by something in the moon’s interior. Further calculations revealed the existence of an ocean.

Scientists believe that the ocean is 12 to 18 miles (20 to 30 kilometers) under the icy surface of Mimas, and that the water is about 45 miles (72 kilometers) deep. With a diameter just under 250 miles (400 kilometers), Mimas is tiny. The ocean makes up about half of its volume.

A photo of Mimas is next to a diagram showing the ice layer and ocean and their depths.
NASA/JPL/Space Science Institute; Infographic Encyclopædia Britannica, Inc.
The ocean under the icy surface of Mimas takes up a large percentage of the moon’s volume.

Mimas isn’t the only moon with an ocean under its surface. Two of Saturn’s other moons, Titan and Enceladus, and two of Jupiter’s moons, Europa and Ganymede, also have hidden oceans. As scientists continue to observe moons, they may find additional oceans to add to the list.

“If Mimas hides a global ocean, this means that liquid water could lie almost anywhere,” Valéry Lainey, one of the scientists involved in the recent discovery, told CNN. “We already have serious candidates for global oceans [on moons such as] Callisto, Dione, and Triton.”

Since liquid water is necessary to support life as we know it, finding oceans in our own solar system raises a lot of intriguing questions. Scientists say the ocean on Mimas is very young—less than 25 million years old. It probably formed too recently for life to have evolved within it. But it’s likely that scientists will continue to take a close look at the icy moons in our solar system for signs of oceans as well as life.


April 1 Is Coming!

© Pai-Shih Lee—Moment/Getty Images

Back in 2022, we marked April Fools’ Day with an In the News page about legendary hoaxes and pranks. 

Did You Know?

Saturn has 146 known moons. The biggest one, Titan, is larger than the planet Mercury.
NASA, ESA/Hubble Heritage Team (STScI/AURA)

A World with No Moon

© Quintessa/; Animation Encyclopædia Britannica, Inc.

We may think our own moon is just an object to look at in the night sky. But what would happen if Earth’s moon somehow disappeared?

  • Ocean tides would be greatly reduced. The Moon’s gravity heavily influences the tides, which churn up the oceans and move water onto the shore. Coastal ecosystems rely on the movement of ocean water. Ocean currents also affect Earth’s climate. Without the Moon, the tides would be much smaller, Earth’s temperatures would be more extreme, and ecosystems would be different.
  • Earth’s axis would change. The Moon’s gravity pulls on Earth, keeping it tilted as it is. Without the Moon, Earth’s tilt, or angle, would be very different. This would affect the amount of sunlight our planet receives, drastically changing our climate.
  • Nights would be much darker. Darker nights wouldn’t just be a bummer. Predators that hunt at night rely on moonlight to help them spot their prey.

Looking for E.T.

U.S. Navy
So far, no one has any proof that life exists beyond Earth. But investigations are ongoing—with some intriguing results, like whatever is happening in this U.S. Navy video.  You can read more about extraterrestrial life at Britannica.





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