When you buy through links in our articles, Future and its syndication partners may earn commission.
Using the James Webb Space Telescope (JWST), astronomers have discovered that Uranus’ moon Ariel may be hiding in a buried ocean of liquid water.
The discovery could provide an answer to a mystery surrounding this Uranian moon that has stumped scientists: the fact that Ariel’s surface is covered in a significant amount of carbon dioxide ice. This is puzzling because, with Uranus and its moons 20 times farther from the sun than Earth, carbon dioxide turns into gas and is lost to space. This means that a process must replenish the carbon dioxide on Ariel’s surface.
Previous theories suggested that this occurred as a result of interactions between Ariel’s surface and charged particles trapped in Uranus’ magnetosphere, which emit ionizing radiation, breaking apart molecules to release carbon dioxide, a process known as “radiolysis”.
But new evidence from JWST suggests that the source of this carbon dioxide is not from outside Ariel, but likely from a buried subsurface ocean.
Relating to: ‘Traffic jam’ around Uranus could solve mystery of faint radiation belts
Chemical elements and molecules leave individual “fingerprints” in spectra because they absorb and emit light at characteristic wavelengths. The team behind this discovery used JWST to collect light spectra from Ariel, which helped them build a picture of the chemical makeup of the Uranus moon.
Comparing this with spectra simulated from a chemical mixture in the laboratory on Earth showed the team that Ariel has some of the most carbon dioxide-rich deposits in the solar system. This not only added 10 millimetres (0.4 inches) to the thickness of the ice on the side of tidally locked Ariel that permanently faces away from Uranus, but also revealed clear carbon monoxide deposits for the first time.
“It shouldn’t be there. You need to get down to 30 kelvins [minus 405 degrees Fahrenheit] “Before the carbon monoxide can become stable,” team leader Richard Cartwright of the Johns Hopkins Applied Physics Laboratory (APL) said in a statement, “the carbon monoxide will have to be actively reformed, no doubt.”
This is because Ariel’s surface temperature is, on average, about 65 degrees Fahrenheit (18 degrees Celsius) warmer than this base temperature.
Cartwright acknowledges that radiolysis could explain some of this restoration. However, observations from the Voyager 2 flyby of Uranus and its moons in 1986 and other recent findings have suggested that the interactions behind the radiolysis may be limited because the magnetic field axis of Uranus and the orbital plane of its moons are about 58 degrees apart.
This means that many of the carbon/oxygen compounds seen on Ariel’s surface could have been created by chemical processes in an ocean of liquid water trapped beneath Ariel’s ice.
Cool customer Ariel may have a volcanic temper
Once created in Ariel’s seepage water ocean, these carbon oxides could escape through cracks in the icy crust of Uranus’ moon or be expelled explosively in powerful eruptions.
Scientists have long suspected that Ariel’s cracked and scarred surface might indicate the presence of active cryovolcanoes, volcanoes that spew icy snow instead of lava. These eruptions can be so powerful that they can hurl material into Uranus’ magnetic field.
Most of the cracks and grooves seen on Ariel’s surface are located on the side facing away from Uranus. If carbon dioxide and carbon monoxide are leaking from these features to Uranus’ surface, this could explain why these compounds are more abundant on this back side of the icy body.
JWST also found more chemical evidence of a subsurface liquid water ocean: Spectral analysis indicated the presence of carbonite minerals, which are salts formed when rock meets and interacts with liquid water.
“If our interpretation of this carbonate feature is correct, that’s a pretty big conclusion because it means it must have formed internally,” Cartwright explained. “That’s something we’ll definitely need to confirm through future observations, modeling, or some combination of techniques.”
Related Stories:
— In quest to find alien life, scientists are looking for extrasolar Earth-Jupiter binaries
— Infrared aurora on Uranus confirmed for first time
— James Webb Space Telescope finds jet stream on Jupiter stronger than a category 5 hurricane
Uranus and its moons have not been visited by a spacecraft since Voyager 2 nearly forty years ago, and this was not even the spacecraft’s primary mission. In 2023, the Planetary Science and Astrobiology Decade Survey highlighted that a dedicated mission to the Uranus system should be prioritized.
Cartwright believes such a mission would provide an opportunity to gather valuable information about the Solar System’s other ice giants, Uranus and Neptune. Such a mission could also provide vital data on their other potentially ocean-bearing moons. This information could then be applied to extrasolar planets, or “exoplanets,” beyond the Solar System.
“All of these new insights underscore how intriguing the Uranus system is,” said team member Ian Cohen, a scientist at NASA’s Applied Physics Laboratory. “Many of us in the planetary science community are really looking forward to a future mission to explore Uranus, whether it’s unlocking the keys to how the solar system formed, better understanding the planet’s complex magnetosphere, or determining whether these moons are potential ocean worlds.”
The team’s research was published Wednesday (July 24) in The Astrophysical Journal Letters.