Scientists: Icy Moon of Saturn Likely Has an Underground Ocean

Researchers say new evidence suggests Saturn's icy moon Mimas likely has a large underground ocean.

Astronomers based their finding on data collected by the American space agency NASA's Cassini spacecraft. Cassini observed Saturn and its more than 140 moons for more than 10 years before ending operations in 2017.

The spacecraft's data covered details about the moon's orbit and rotation. Researchers reported the data provided the best evidence yet of a hidden ocean about 20 to 30 kilometers beneath the frozen surface.

Mimas is a relatively small moon, about 400 kilometers wide. Researchers say Mimas lacks formations on its surface found on other moons, which suggest the presence of underground water. These can include a broken surface as well as geyser activity.

Scientists said the fact that Mimas did not have unusual surface formations made it an unlikely candidate for an underground ocean.

Valery Lainey, of the Paris Observatory, was co-author of a study describing the research in the publication Nature. "Mimas was probably the most unlikely place to look for a global ocean — and liquid water more generally," he said in an email to the Associated Press.

Lainey added, "So that looks like a potential(ly) habitable world. But nobody knows how much time is needed for life to arise."

The amount of water thought to exist below the surface of Mimas would represent just 1.2 to 1.4 percent of Earth's oceans, Lainey said. That is because of the moon's small size.

However, Mimas does have a very large crater caused by a crash with a space object. For this reason, the appearance of the moon has been compared to the fictional "Death Star" space station in the popular movie series Star Wars.

English astronomer William Herschel discovered Mimas in 1789. It is named after a giant in Greek mythology.

An article appearing with the study in Nature was co-written by Matija Cuk of the SETI Institute research center and Alyssa Rose Rhoden of the Southwest Research Institute. The two were not part of the study. But they wrote that they find the idea that a small, icy moon can contain young oceans "inspiring."

The researchers said the underground ocean appears to have formed recently in space terms, possibly between 5 and 15 million years ago. Lainey said the ocean would likely have an overall temperature of around zero degrees Celsius. But the temperature at the seafloor might be much warmer.

The fact that the water is in contact with the moon's rocky center may create the right complex chemical conditions to support life. But the researchers noted that because the ocean is believed to be young, it might not be ideal for life to form there.

Scientists have said in the past that another moon of Saturn, Enceladus, might possess the warmth, water and chemical compounds necessary to support life. But because Mimas' ocean is so young, it "might be a challenge for life's development," study co-writer Gabriel Tobie told Reuters. Tobie is a scientist at the French scientific research agency CNRS and The University of Nantes.

However, Tobie added, "Nobody knows how long life needs to emerge from a suitable environment. Mimas may offer a unique opportunity to explore the first stage of life's development."

I'm Bryan Lynn.

The Associated Press and Reuters reported on this story. Bryan Lynn adapted the reports for VOA Learning English.

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rotate – v. to turn in a circular direction

mythology –n. old, stories that belong to certain cultures and which appear again and again in writing and art

geyser – n. a hole in the ground from which hot water and steam come out

habitable – adj. having the ability to support life

potential – n. existing in possibility

fictional – adj. not existing in real life

inspire – v. to make someone feel that they want to do something and can do it

challenge – n. something difficult that tests one's ability or determination

emerge – v. to appear somewhere

opportunity – n. a chance to do something