CO2 reveals hidden ocean on Uranus’ moon Ariel

Jul 29. () –

The abundant carbon dioxide and other molecules detected on Neptune’s moon Ariel are emerging from its interior, possibly even from an underground liquid oceanreveals a new study.

Using the James Webb Space Telescope to collect chemical spectra of the moon and then compare them to spectra of chemical mixtures simulated in the laboratory, a research team led by Richard Cartwright of the Johns Hopkins Applied Physics Laboratory (APL) found that Ariel has some of the richest deposits of carbon dioxide in the solar system, totaling an estimated thickness of 10 millimeters (0.4 inches) or more on the moon’s trailing hemisphere. Among those deposits was another puzzling find: the first clear signals of carbon monoxide. The finding is published in The Astrophysical Journal Letters.

“It just shouldn’t be there. You have to get it down to 30 kelvin (minus 242 degrees Celsius) for the carbon monoxide to stabilize,” Cartwright said. it’s a statementAriel’s surface temperature, meanwhile, is on average about 30 degrees warmer. “Carbon monoxide would have to be actively replenished, no doubt.”

Radiolysis could be responsible for some of that replenishment, he added. Laboratory experiments have shown that radiation bombardment of water ice mixed with carbon-rich material can produce both carbon dioxide and carbon monoxide. Radiolysis may therefore provide a source of replenishment. and explain the rich abundance of both molecules in Ariel’s trailing hemisphere.

But many questions remain about Uranus’ magnetosphere and the extent of its interactions with the planet’s moons. Even during Voyager 2’s flyby of Uranus nearly 40 years ago, scientists suspected that such interactions might be limited because the axis of Uranus’ magnetic field and the orbital plane of its moons are offset from each other by about 58 degrees. Recent models have supported that prediction.

Instead, most of the carbon oxides may come from chemical processes that occurred (or are still occurring) in an ocean of water beneath Ariel’s icy surface, escaping through cracks in the moon’s icy exterior, or possibly even through eruptive plumes.

In addition, new spectral observations suggest that Ariel’s surface may also host carbonate minerals, salts that can only be formed through the interaction of liquid water with rocks.

“If our interpretation of that carbonate feature is correct, then it’s a pretty important result because it means it had to have formed in the interior,” Cartwright said. “That’s something we absolutely need to confirm, whether through future observations, modeling or some combination of techniques.”

With Ariel’s surface covered in gash-like canyons, crisscrossing grooves, and smooth spots thought to be from cryovolcanic outpourings, researchers have already suspected that the moon was or may still be active. A 2023 study led by APL’s Ian Cohen even suggested that Ariel and/or its sister moon Miranda could be emitting material into Uranus’ magnetosphere, possibly even via plumes.

“All of these new insights underscore just how compelling the Uranus system is,” Cohen said. “Whether it’s unlocking clues to how the solar system formed, better understanding the planet’s complex magnetosphere, or determining whether these moons are possible ocean worlds, many of us in the planetary science community are eager for a future mission to explore Uranus.”

PRIORITY ROBOTIC MISSION

In 2023, through its decadal Planetary Science and Astrobiology survey, the planetary science community prioritized the first mission dedicated to Uranusraising hopes that a scientific voyage to the turquoise ice giant is on the horizon.

Cartwright sees it as a opportunity to collect valuable data about the solar system’s ice giants and their potentially oceanic moons, which have applications for worlds being discovered in other star systems.

But it’s also an opportunity to finally get concrete answers that are only possible by being in the system. For example, most of Ariel’s observed grooves (supposed openings to its interior) are on its trailing side. If carbon dioxide and carbon monoxide somehow leak through those grooves, could provide an alternative explanation for why they are much more abundant on the back side of Ariel.