New observations by the James Webb Space Telescope suggest that an icy moon around Uranus may have an underground liquid ocean.
Ariel is one of 27 moons around Uranus, the seventh planet from the sun and the third largest planet in the solar system. It’s one of four moons that scientists have long been interested in as part of a search for water across the solar system, the others being Umbriel, Titania and Oberon.
Ariel is named after a character in William Shakespeare’s “The Tempest,” while Titania and Oberon are from his “A Midsummer Night’s Dream.”
Carbon Dioxide
As part of a planned “Moons of Uranus” project, scientists used JWST to observe the four moons for 21 hours, searching for traces of ammonia, organic molecules, water and carbon dioxide ice.
Carbon dioxide ice is thought to be unlikely at Uranus because at that distance from the sun—20 times farther than Earth—it turns to gas.
However, Ariel’s surface—which has canyons, grooves and smooth regions—was found to contain carbon dioxide ice, particularly on the side of the moon that faces away from the direction it orbits.
Liquid Ocean?
Where the carbon dioxide ice is coming from is a mystery, but the research paper—published in The Astrophysical Journal Letters—argues that it may be coming from a liquid ocean beneath the surface of Ariel.
“It just shouldn’t be there,” said Richard Cartwright, lead author, from the John Hopkins Applied Physics Laboratory in Laurel, Maryland. “You’ve got to get down to 30 kelvins [minus 405 degrees Fahrenheit] before carbon monoxide is stable.” Ariel’s surface temperature averages around 65 degrees Fahrenheit warmer.
Another theory is that the carbon dioxide ice at Ariel is produced by molecules being broken down by radiation in Uranus’ magnetic field.
Geologically Active
Underground oceans are intriguing, but not unusual. They exist on Europa, Ganymede and Callisto, three of Jupiter’s largest moons, and Enceladus, Titan and Mimas at Saturn. Underground oceans fascinate planetary scientists because only geologically active worlds are thought to have any chance of hosting oceans.
The carbon dioxide ice on Ariel is thought to be produced by chemical processes in the underground ocean and escapes onto its surface via cracks in its ice—possibly as plumes.
The research also found hints of carbonates on Ariel’s surface, minerals that can only form when water interacts with rock. “If our interpretation of that carbonate feature is correct, then that is a pretty big result because it means it had to form in the interior,” said Cartwright. “That’s something we absolutely need to confirm, either through future observations, modeling or some combination of techniques.”
Mission To Uranus?
Not much is known about Ariel. NASA’s Voyager 2 photographed it in 1986 during its tour of the planets, but only a third of its surface was imaged. Hints that Ariel—and other moons of Uranus—are geologically active, and possibly ocean worlds, are one reason why planetary scientists have recommended a NASA mission.
The Uranus Orbiter and Probe (UOP) is a concept for a mission to tour the Uranus system. Launch opportunities are in the early 2030s, and the journey will take 12—to 13 years. If NASA does want to send a mission, it will need to act quickly because a gravity-assist from Jupiter is vital, but something that’s only possible every 12 years or so.
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Wishing you clear skies and wide eyes.
