In the extremely dark and cold reaches of the solar system, the clues about a liquid ocean on Ariel are truly astonishing.
The moon Ariel of Uranus, named after a spirit in William Shakespeare’s play “The Tempest”, has revealed indirect signs of a subsurface ocean in new observational data from the James Webb Space Telescope.
The surprising sign found by James Webb is the unusual presence of carbon dioxide ice on the surface, particularly dense on the “far side”, which refers to the side always facing away in the moon’s orbit around its parent planet.
This fact is surprising because, given the frigid temperatures of the Uranian system – an average of 2.9 billion kilometers away – carbon dioxide should easily convert to gas and escape into space.
Scientists have hypothesized that something is supplying carbon dioxide to the surface of Ariel.
Ariel may have a subsurface ocean beneath its icy crust, with Uranus visible on the horizon – (AI illustration: Anh Thư).
One previous opinion supported the idea that the interaction between the moon’s surface and charged particles in Uranus’s magnetosphere generates carbon dioxide through a process of radiolysis, where molecules are broken down by ionizing radiation.
However, the research team led by scientists from the Johns Hopkins University Applied Physics Laboratory has found a different answer.
Publishing their findings in the scientific journal Astrophysical Journal Letters, this team reported that they used NASA’s James Webb Space Telescope to collect the chemical spectra of the moon, which were then compared with laboratory-simulated chemical spectra.
The results indicate that Ariel has the largest deposits of carbon dioxide in the Solar System, estimated to be up to 10mm or more thick on the far side.
Among these deposits is another puzzling discovery: the first clear signals of carbon monoxide.
“It shouldn’t be there. You have to drop down to -243 degrees Celsius before carbon monoxide stabilizes,” said Dr. Richard Cartwright, the lead author.
Meanwhile, the average surface temperature of Ariel is about -208 degrees Celsius, suggesting that this carbon monoxide must be actively replenished.
Radiation may still account for some of that replenishment, but many questions remain regarding the magnetosphere of Uranus and 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 Uranus’s magnetic axis and the orbital plane of its moons are tilted as much as 58 degrees apart.
Therefore, for these factors to be present in the way they are found on the icy moon, a subsurface ocean would be necessary to facilitate some chemical processes, pushing the aforementioned materials out through cracks in the icy crust or via geysers.
Furthermore, new spectroscopic observations suggest that Ariel’s surface may also contain carbonate minerals, which can only form through the interaction of liquid water with rock.
It is still too early to determine whether this ocean could harbor life, but liquid water is always a top indicator suggesting potential life.
Thus, Ariel will be an intriguing world for future space missions to target.
