Cataclysmic collisions in the outer solar system do not necessarily destroy the potential for underground oceans on icy moons, according to new simulations led by the University of Maryland. The research reveals that larger frozen moons can retain or even thicken their subsurface liquid water layers despite being shattered apart.
The outer reaches of the solar system possess a remarkably violent history. For 4.5 billion years, small celestial bodies and frozen moons have faced continuous bombardment from impacts severe enough to break them entirely into pieces. In some cases, mutual gravity pulls the scattered fragments back together into patchwork worlds like Uranus’ moon Miranda or Saturn’s fragmented relic, Iapetus. For years, planetary scientists questioned whether these catastrophic disruptions spelled doom for any subsurface liquid water hidden beneath the ice.
To find out, an international research team led by Marc Neveu of the University of Maryland investigated whether moon-shattering impacts wipe out habitable environments or leave them intact. The team included co-authors Raluca Rufu, Alyssa Rhoden, and Kevin Walsh from the Southwest Research Institute in Boulder, Colorado, alongside Yuval Steinberg from the Weizmann Institute of Science in Israel.
Simulating Outer Solar System Catastrophes
The investigators tackled the problem by combining two distinct modeling methods to trace how icy moons evolve over billions of years. The first approach simulated the raw physics of a cosmic collision, tracking millions of rock and ice fragments as they shattered, absorbed intense thermal energy, and eventually reassembled. The second simulation modeled the internal thermal profile of each moon over a 4.5-billion-year timeline, showing how core heat escapes to maintain liquid water layers.
By coupling these methods, the team tested moons built at two different scales: roughly 620 miles and 1,240 miles across. The models subjected these simulated bodies to the most extreme disruptions imaginable. As Neveu noted in a published statement, These simulations were pretty much the biggest collisions we could come up with.
If those don’t make a difference, it’s unlikely smaller ones would either.
Marc Neveu, University of Maryland
Why Size Dictates Ocean Survival
The simulations demonstrated that a moon’s physical scale determines whether its hidden ocean survives a cataclysm. For smaller bodies under 620 miles wide, an impact usually spells the end of any subsurface liquid. Before a disruption, a small moon often retains an insulating jumble of mixed ice and rock that traps interior warmth. Once shattered and reassembled, however, the denser rock sinks to the center while clean ice floats upward. This loss of the insulating blanket allows heat to bleed rapidly into space, preventing an ocean from forming or causing an existing one to freeze solid.
Larger worlds experience the exact opposite dynamic. When a massive moon reforms after a violent crash, the sheer mechanical energy of the impact converts into internal heat. This extra warmth can actually deepen and thicken an existing subsurface ocean for a couple of billion years. Across all sizes, the models indicated that collisions cannot spontaneously generate an ocean from a previously frozen world, but they rarely destroy one that was already there.
What we found was that those big collisions don’t really matter as far as oceans are concerned. If there was an ocean before, there’s likely to be an ocean after and vice versa.
Marc Neveu, University of Maryland, via Space
Clues on Saturn’s Moon Rhea
These theoretical models offer a potential explanation for unusual geological features observed on real worlds across the outer solar system, including Saturn’s moons Mimas, Enceladus, Tethys, Dione, and Rhea, as well as Uranus’ moons Miranda, Ariel, Umbriel, Titania, and Oberon, plus Neptune’s large moon Triton.
Rhea, Saturn’s second-largest moon at 949 miles across, displays ancient impact craters that appear unusually softened and smoothed out. Neveu compared the phenomenon to a winter snowman deforming as ambient warmth melts its features from within. The team’s findings suggest that a long-ago impact boosted an interior ocean, driving the heat that altered the moon’s surface appearance from below rather than direct sunlight.
Implications for Future Space Missions
Understanding the resilience of buried oceans directly shapes how planetary scientists plan future exploration campaigns. Space agencies look to these hidden liquid reservoirs as prime targets in the search for extraterrestrial life, hunting for gravitational anomalies, salty surface deposits, and cryovolcanic eruptions.
Knowing which bodies can maintain liquid water through catastrophic disruptions helps researchers design instruments tailored to the specific environment they expect to find. As Neveu pointed out regarding instrument sensitivity and target ecosystems, mission architects must weigh whether they are searching for sparse microbial traces or more abundant life forms.