Cosmic collisions don't destroy hidden oceans on icy moons, study finds

Beneath the frozen crusts of moons orbiting Saturn, Uranus, and Neptune lie oceans of liquid water—some of the most compelling places in the solar system to search for life. But these worlds exist in a violent neighborhood. Scientists have long suspected that many of today's moons are reassembled fragments of earlier generations, shattered and reformed from cosmic collisions. The question that has haunted researchers is whether these catastrophic impacts destroy the hidden oceans entirely, erasing any possibility of life, or whether something more subtle happens.

A study led by Marc Neveu at the University of Maryland, published in Nature Astronomy on August 21, 2026, offers a surprising answer: the collisions barely matter. Even the most violent cosmic crashes the researchers could simulate did not fundamentally change whether a moon could sustain an ocean. "If there was an ocean before, there's likely to be an ocean after and vice versa," Neveu explained. The finding caught the research team—which included collaborators from the Southwest Research Institute in Colorado and the Weizmann Institute of Science in Israel—off guard. "These simulations were pretty much the biggest collisions we could come up with," Neveu said. "If those didn't make a difference, it's unlikely smaller ones would either."

To reach this conclusion, the researchers combined two distinct computational approaches. One simulated the violent physics of impact itself, tracking how millions of rock and ice fragments shatter, heat up, and clump back together in the aftermath. The other modeled the slow thermal evolution of a moon's interior over billions of years, following how heat builds and dissipates from the core and whether conditions allow ice to melt into liquid water. By linking these two methods, the team could follow the complete lifecycle of simulated moons roughly 500 and 1,000 kilometers in radius as they were struck by smaller space rocks, blown apart, and reassembled. They then fast-forwarded through 4.5 billion years of each moon's evolution after impact.

The results revealed that moon size plays a larger role than expected in determining what happens after a collision. In larger moons, the energy released by impact converts into extra heat that can actually thicken an existing ocean for a couple billion years afterward. Smaller moons tell a different story. Before a collision, these worlds maintain a jumbled outer layer of mixed ice and rock that acts like an insulating blanket, trapping the internal heat needed to sustain an ocean. The impact shakes this layer apart, and when the moon reforms, rock sinks toward the center while ice rises to the surface. This reorganization removes the insulating blanket, making it harder for the smaller moon to maintain an ocean. Yet even in this scenario, the collision did not create an ocean where none existed before—it simply altered the conditions around an ocean that was already there.

The findings apply directly to real worlds that space agencies plan to explore. Saturn's mid-sized moons Mimas, Enceladus, Tethys, Dione, and Rhea; Uranus's moons including Miranda, Ariel, Umbriel, Titania, and Oberon; and Neptune's large moon Triton all fit the parameters of the simulations. Saturn's moon Rhea has already caught the team's attention as a possible test case. Its ancient craters appear strangely smooth and softened, as if warmed from within—a pattern Neveu compared to a snowman melting in spring warmth. "It wasn't the sun," he noted. "The heat came from below. A long-ago collision that boosted an interior ocean could help explain why the moon appears that way."

These findings carry immediate practical weight for NASA and the broader planetary science community as they plan future missions to the outer solar system. Knowing which moons are most likely to harbor water helps determine where to send spacecraft and what instruments to prioritize. Scientists will search for gravitational signatures of hidden oceans, salty deposits on the surface, and icy cryovolcanoes that might hint at subsurface activity. The nature of potential life itself shapes the search strategy. "If there's only a handful of microbes, you won't be designing the same kind of search mission as you would if the ocean were full of whales," Neveu said. "The type of life we're looking for will determine what kind of tools we need to develop."

Yet Neveu emphasized that a moon's collision history is only one piece of a much larger puzzle. Other factors—particularly the heat generated by tidal forces as moons orbit their parent planets—matter at least as much in determining whether an ocean can exist and persist. The researcher's broader ambition is to model entire moon systems in motion, watching how orbital mechanics drive moons toward collision courses and how those impacts reshape their interiors. "Down the line, I would love to press play on a moon system and watch how the moons move, how they smash into each other and how their interiors change as a result," he said. "Maybe then we can reconstruct what happened around Saturn, Uranus and Neptune." For now, this study clears away one major uncertainty: the violent history of the outer solar system did not erase the oceans that might harbor life.