New research indicates that Uranus's moon Miranda may be hiding a subsurface ocean, challenging many assumptions about its history and composition. The finding suggests that Miranda could have been warmed by resonance to produce and maintain a subsurface ocean.
The study, titled "Constraining Ocean and Ice Shell Thickness on Miranda from Surface Geological Structures and Stress Modeling," was conducted by lead author Caleb Strom, a graduate student at the University of North Dakota. He worked with co-researchers Tom Nordheim and Alex Patthoff of the Planetary Science Institute in Arizona. The team set out to explain Miranda's enigmatic geology by reverse-engineering its surface features. They developed a computer model to work backward from Miranda's current surface and test several possible structures of its interior.
They mapped Miranda's surface features, including its cracks, ridges, and unique trapezoidal coronae. The team matched the predicted stress patterns with the actual surface geology of Miranda, finding that a thin crust is most likely to result in sufficient stress magnitude to cause brittle failure of ice on its surface. Their model indicated that the moon had a vast ocean beneath its icy crust 100 to 500 million years ago.
Miranda's icy crust is probably no more than 30 kilometers thick, and the ocean beneath it is at least 100 kilometers deep. This intense heating event may have allowed for a subsurface ocean approximately 100 kilometers thick, which could have filled almost half of Miranda's body. "That result was a great surprise for the team," Caleb Strom said.
The researchers believe that the key to creating that ocean were the tidal forces between Miranda and nearby moons. Tidal heating is responsible for the potential subsurface ocean on Miranda, likely warmed by resonance with nearby moons. These regular gravitational tugs can be amplified by orbital resonances—a configuration in which the period of each moon around a planet is an exact integer of the periods of the others. Such tidal forces can periodically deform the moons like rubber balls, generating friction and heat that keep the interiors warm and liquid.
"Numerical simulations have suggested that Miranda and its neighboring moons probably had that resonance in the past, offering a potential mechanism that could have heated the interior of Miranda to produce and maintain an underground ocean," the authors conclude. They explain in their research: "Our results show that a thin crust (~30 km) is most likely to result in sufficient stress magnitude to cause brittle failure of ice on Miranda's surface."
However, the team does not believe that the interior of Miranda has completely frozen yet. If the ocean had completely frozen, it would have expanded and caused surface cracks, which are not present on Miranda. The researchers don't think Miranda's ocean has completely frozen yet, and with its small size and old age, scientists initially thought it would likely be a frozen ball of ice. "But the suggestion of an ocean inside one of the most distant moons in the solar system is remarkable," Caleb Strom said, highlighting the potential for habitability and life in ocean moons.
Co-researcher Tom Nordheim added, "It helps build on the story that some of these moons at Uranus may be really interesting—that there may be several ocean worlds around one of the most distant planets in our solar system, which is both exciting and bizarre."
Comparisons have been made between Miranda and Saturn's moon Enceladus. Before the Cassini spacecraft arrived in 2004, many scientists thought Enceladus was a frozen ball of ice and rock. "Few scientists expected Enceladus to be geologically active," said co-author Alex Patthoff. "However, it's shooting water vapor and ice out of its southern hemisphere as we speak." Since both Enceladus and Miranda are roughly the same size and may have similar ice shells, it increases the chances that Miranda also has an ocean.
Other recent research suggests that Miranda could be more like Enceladus than previously thought. According to a 2023 study led by APL's Ian Cohen, Miranda may be actively releasing material into space, similar to Enceladus. These findings suggest that Miranda and other moons of Uranus could be future targets for studying habitability and life.
Attempts to understand Miranda are limited by the amount of data that Voyager 2 provided during its brief flyby in 1986. "We won't know for sure that it even has an ocean until we go back and collect more data," Nordheim said. "For now, we're excited by the possibilities and eager to return to study Uranus and its potential ocean moons in depth." This latest study, led by Caleb Strom and APL's Tom Nordheim, is part of a broader effort to uncover the secrets of these mysterious moons and the unusual planet they orbit.
Perhaps one day, Miranda and other moons of Uranus will get missions of their own. The prospect of an ocean beneath Miranda's surface is not only fascinating but also opens up new avenues in the search for life in the solar system. With continued research and potential future missions, scientists hope to learn more about these distant worlds and their potential to harbor life.
Sources: Phys.org, EarthSky, RPP noticias, Universe Today
This article was written in collaboration with generative AI company Alchemiq