SAN ANTONIO — September 8, 2026 — Southwest Research Institute (SwRI) scientists provided simulations to understand the role disruptive impacts play on icy moons with subsurface oceans in our solar system. A recent paper published in the journal Nature Astronomy concludes that disruptive impacts can affect the presence and persistence of subsurface oceans in these moons, but do not seem to create new oceans.
Many icy moons of the outer Solar System are candidate ocean worlds — moons that may harbor large volumes of liquid water under their icy crusts — including several smaller moons of Saturn and Uranus. Curiously, these same moon systems possess characteristics that have led scientists to question whether they are the original moons that formed around their parent planets early in Solar System history. Rather, it has been suggested that most or all of the smaller (radius < 1000 km) moons around Saturn and Uranus were disrupted in large collisions.
"For the moons of Saturn, disruptive collisions have been proposed even within the last 100 million years, suggesting that the candidate ocean moons we see today reassembled relatively recently out of the collisional debris of older moons," said Dr. Alyssa Rhoden, a staff scientist in SwRI's Solar System Science and Exploration Division in Boulder, Colorado, and a co-author of the paper. "This proposition led us to question whether reassembled moons still form oceans."
To answer this question, the team combined a smoothed particle hydrodynamics (SPH) model to simulate collisions with a thermal-structural evolution model to simulate the evolution of moon impacts. This combination allowed scientists to compare moons pre-impact, post-impact and without a collision. Disruptive impacts are common, especially during the formative years of the solar system. These impacts would significantly alter the makeup of the moon, not just leave a crater.
"Our definition of a disruptive impact was that the biggest remaining fragment had to be less than half the size of the initial target," Rhoden said. "So, you are really breaking this thing up."
This research considered whether these kinds of impacts played a role in the formation of oceans. "Imagine a moon that is small and frozen and isn't doing anything very interesting. If you throw something at it and cause a big collision, would that impart enough energy to cause an ocean to form?" Rhoden asked. "Our models indicated that is actually incredibly difficult. Most of the time a small moon experiencing a disruption may lose its ocean or prevent an ocean from forming in the first place."
The study found that overall, large-scale collisions only affect ocean thickness and longevity, but do not contribute to creating new oceans.
"That would seem to be counterintuitive. Introducing more energy to the system could melt the ice and create oceans," said SwRI's Dr. Raluca Rufu, another co-author. "But this energy dissipates very quickly, which actually works against forming oceans."
Rhoden compares it to baking potatoes. "When you make a baked potato versus baking French fries, the smaller pieces heat up and cool down much faster than a whole potato. So, the same thing happens when you blow up a small moon. All the pieces lose their heat very quickly."
While disruptive collisions may not promote the formation of oceans, they do result in ice-rock differentiation. A moon may have chunks of rock and ice all mixed together, but, in aftermath of the collision, the ice briefly melts. Then heavier material sinks to the core before the water refreezes, forming a thicker coating of ice around it.
"When everything consolidates after a collision, you will end up with a more substantial core and a thicker layer of ice," Rufu said. "When moons had subsurface oceans prior to impact, larger moons — with a radius of 1,000 kilometers or more — might keep it, but smaller moons tend to lose them."
Outer solar system moons span a wide range of physical and orbital characteristics, and the parameters that could have led to disruptive collisions are not well constrained. Therefore, more work is needed to determine whether any conditions can promote ocean formation in smaller reassembled moons.
"For now, though, it seems unlikely that moons like Saturn's Enceladus or Dione — which are both thought to harbor oceans today — would have been disrupted and reassembled in the past 100 million years," Rhoden said.
Dr. Marc Neveu of the University of Maryland and NASA's Goddard Space Flight Center led the research and was first author of the paper "The Role of Disruptive Impacts on Ocean Generation and Longevity in Icy Moons" published this month in Nature Astronomy. It can be accessed at: https://doi.org/10.1038/s41550-026-02955-x .
Watch a simulation: https://bcove.video/4xFSePz
