Artist's impression of Ariel orbiting among the rings of Uranus.
Getty
New observations from the James Webb Space Telescope suggest that an icy moon around Uranus may harbor a liquid ocean beneath its surface.
Ariel is one of 27 moons that orbit Uranus, the seventh planet from the Sun and the third largest planet in the solar system. It is one of four moons that have long been of interest to scientists as part of the solar system-wide search for water; the other three are Umbriel, Titania, and Oberon.
Ariel is named after a character in William Shakespeare's The Tempest, while Titania and Oberon are named after characters in A Midsummer Night's Dream.
carbon dioxide
As part of the planned “Moons of Uranus” project, scientists will use the JWST to observe the four moons for 21 hours, looking for signs of ammonia, organic molecules, water, and carbon dioxide ice.
Carbon dioxide ice is thought to be unlikely to exist on Uranus because it is 20 times farther from the Sun than Earth, meaning that any carbon dioxide ice would turn into gas.
But Ariel's surface, which has canyons, grooves and smooth areas, was found to contain carbon dioxide ice, especially on the side facing away from its orbit.
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A liquid ocean?
Where the carbon dioxide ice comes from is a mystery, but a study published in the Astrophysical Journal Letters argues that it could come from a liquid ocean beneath Ariel's surface.
“It can't be there,” said lead author Richard Cartwright of the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland. “For carbon monoxide to be stable, it has to get down to 30 Kelvin (minus 405 Fahrenheit).” Ariel's surface temperature is about 65 degrees Fahrenheit warmer, on average.
Another theory is that Ariel's carbon dioxide ice was formed when radiation from Uranus' magnetic field broke down the molecules.
Geologically Active
Subsurface oceans are intriguing but not uncommon: They exist on Jupiter's three largest moons – Europa, Ganymede, and Callisto – and on Saturn's Enceladus, Titan, and Mimas. Subsurface oceans fascinate planetary scientists because they are thought to exist only on geologically active planets.
Ariel's carbon dioxide ice is thought to be produced by chemical reactions in a subsurface ocean and erupts to the surface through cracks in the ice, possibly appearing as smoke.
The study also found traces of the presence of carbonates on Ariel's surface, a mineral that forms only when water interacts with rocks. “If our interpretation of the carbonate signature is correct, it's a huge accomplishment because it means it must have formed internally,” Cartwright said. “This is something that absolutely needs to be confirmed through further observations, modeling, or a combination of techniques.”
Image of Uranus' moon Ariel by Voyager 2. (Photo by Universal History Archive/Universal … (+) Images Group via Getty Images)
Universal Image Group via Getty Images
A mission to Uranus?
Not much is known about Ariel. NASA's Voyager 2 spacecraft photographed it while orbiting the planet in 1986, but only captured a third of its surface. Hints that Ariel and Uranus' other moons are geologically active and possibly ocean worlds are one reason planetary scientists recommend a NASA mission.
The Uranus Orbiter Probe (UOP) is a proposed mission around the Uranus system. Its launch is planned for the early 2030s, with the journey taking 12 to 13 years. If NASA wants to send a mission, they'll need to act fast, as they'll need Jupiter's gravity assist, which is only feasible once every 12 years or so.
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