Ariel, the brightest and second-closest moon of Uranus, has made headlines as of late. New research indicates that it could have once housed an ocean more than 100 miles deep underneath its crust. Ariel is the fourth-largest moon in the Uranian system, measuring 720 miles (1,159 kilometers) across. Its surface features clearly show that there is extensive erosion, raising questions about a dynamic geological past.
The study is the latest development in a broader effort to understand the subsurface composition of Uranus’ moons. It implies that Ariel used to have a subsurface ocean at least 100 miles (170 kilometers) deep. This depth is especially remarkable given that Earth’s Pacific Ocean is on average just 2.5 miles (4 kilometers) deep. Researchers argued that because fractures are found all over Ariel’s surface, a subsurface ocean must exist.
Ariel’s eccentricity today is about 40 times smaller than it once was. It would have taken a high eccentricity of at least 0.03 to allow the creation of its unique geological features. Her previous orbit was four times as eccentric as Europa’s. This indicates that Ariel has experienced a transformation in its character over nearly three decades.
Earth’s moon has an incredibly stark contrast of geological variety. Ancient craters lie adjacent to all-new smooth plains, possibly sculpted by cryovolcanism. This striking landscape reflects a deep, turbulent history marked by both old and new geological processes.
Tom Nordheim, a member of the research team, underscored the relevance of their findings.
“We are finding evidence that the Uranus system may harbor twin ocean worlds.” – Tom Nordheim
We mapped structure using larger surface features in this study. Then, we used a computer model to calculate the tidal stresses that Ariel is subjected to as it orbits around Uranus. Together with fellow researcher Alex Patthoff, he walked us through the innovative methodology that made this study so unique.
“First, we mapped out the larger structures that we see on the surface, then we used a computer program to model the tidal stresses on the surface, which result from distortion of Ariel from soccer ball-shaped to slight football-shaped and back as it moves closer and farther from Uranus during its orbit.” – Alex Patthoff
These results indicate that Ariel’s surface fractures were likely the products of one of two scenarios. Either there was a thick ice shell over a deep ocean, or the moon was once more eccentric with a shallower ocean under a thin ice shell.
“Ariel is pretty unique in terms of icy moons.” – Alex Patthoff
The research team has trained their observations at the southern hemispheres of Ariel, as well as its neighboring moon Miranda. Still, their findings can serve as a window into predicting what kinds of geological features will be found on those unexplored northern hemispheres.
“Unfortunately, we’ve only seen the southern hemispheres of Ariel and Miranda. But our results can give us predictions of what a future spacecraft might see on the moons’ unimaged northern hemispheres, such as the location of fractures and ridges there. Ultimately, we just need to go back to the Uranus system and see for ourselves.” – Tom Nordheim