Chaos may have ruled the early solar system far more dramatically than previously thought. New simulations suggest a now-vanished third ice giant could have triggered violent planetary encounters that disrupted the moons of Jupiter and Uranus, potentially destroying some and helping create others, including Uranus’s mysterious moon Miranda.
For billions of years, the solar system has appeared remarkably stable. The planets follow predictable paths, and their moons circle them in orderly fashion. But new research suggests that beneath this calm exterior lies a far more turbulent past—one that may have involved an extra giant planet that no longer exists.
According to a study published in Icarus, the early outer solar system may have contained a third ice giant alongside Uranus and Neptune. If so, that lost world could have played a major role in a period of planetary upheaval that reshaped the architecture of the solar system and dramatically altered the fate of several moons.
Revisiting a Chaotic Era
The study focuses on a turbulent chapter in solar system history known as the Nice Model instability. This period occurred shortly after the planets formed, roughly 4 billion to 4.5 billion years ago, when the giant planets experienced major orbital changes.
During this instability, the orbits of Jupiter, Saturn, Uranus, and Neptune became highly unstable. The giant planets passed unusually close to one another, exerting powerful gravitational forces that repeatedly altered their trajectories.
Eventually, the planets settled into the arrangement seen today. Yet one longstanding mystery has remained unresolved: how did their regular moons survive such extreme gravitational turmoil?
Simulating the Early Solar System
To investigate that question, researchers examined 122 computer simulations selected from thousands of possible scenarios. These particular simulations were chosen because they successfully reproduced key characteristics of the modern outer solar system.
The models tracked the complex gravitational interactions among planets, moons, the Sun, and passing space rocks over millions of years. Researchers tested versions of the solar system that began with five or six giant planets, reflecting current Nice Model scenarios in which one or two additional giant planets were eventually expelled from the solar system.
By recreating these ancient conditions, the team sought to understand whether the moon systems of Jupiter and Uranus could have endured the instability intact.
Survival Was Rare
The results painted a surprisingly destructive picture.
According to the researchers, the chances of preserving the moon systems of both Jupiter and Uranus were extremely low. The study found that the survival probability of the Jovian and Uranian moon systems was less than 15%.
Even more striking, among all the tested scenarios, only one simulation allowed both the original planets and their moons to survive together.
These findings suggest that the giant planet instability may have been far more disruptive to planetary satellite systems than previously appreciated.
Uranus Appears Especially Vulnerable
The simulations revealed that close encounters involving Uranus were particularly devastating.
When other giant planets passed too near the ice giant, their gravitational influence frequently destabilized Uranus’s moons. Rather than being flung harmlessly into space, many of these moons were driven onto collision courses with one another.
The resulting impacts would have been violent, producing large quantities of icy debris. Over time, that debris could have gradually merged into new moons.
This scenario offers a possible explanation for the origin of Miranda, one of Uranus’s moons. The researchers suggest that Miranda may have formed from the remnants of earlier moons that were shattered during these catastrophic collisions.
Multiple Catastrophes May Have Struck Uranus’s Moons
The study points to an even more dramatic history for Uranus’s satellite system.
According to the researchers, the moons of Uranus were likely pushed toward collisions on at least two separate occasions. One episode was linked to the event that tilted Uranus, while another was associated with the giant planet instability itself.
This means the Uranian moon system may have experienced repeated cycles of disruption and reconstruction throughout its early history.
Rather than remaining unchanged since their formation, some moons may be the products of ancient destruction, assembled from debris left behind by previous generations of satellites.
A Missing Planet in the Story
One of the study’s most intriguing implications is the possible role of an additional ice giant.
The simulations were based on versions of the Nice Model that include one or two giant planets no longer present today. In these scenarios, gravitational interactions eventually eject the extra worlds from the solar system.
If such a planet once existed, it could have contributed significantly to the close encounters that destabilized the outer solar system. Its disappearance may help explain why the modern planetary arrangement appears comparatively orderly despite evidence of a much more chaotic beginning.
However, the study does not claim definitive proof that a lost ice giant existed. Instead, it shows how scenarios involving additional giant planets can reproduce features of the solar system while also accounting for major disruptions among planetary moons.
Why This Matters
This research offers a fresh perspective on how the solar system evolved into its present form. Rather than viewing moons as unchanged relics from planetary formation, the findings suggest some may be survivors—or even products—of ancient cosmic catastrophes.
The study also highlights how fragile planetary systems can be during their earliest stages. If giant planets underwent repeated close encounters, the moons orbiting them may have been reshaped, destroyed, and rebuilt multiple times before stability finally emerged.
While the researchers emphasize that simulations cannot capture every detail of the solar system’s past and that further modeling is needed to determine the fate of individual moons, the work strengthens the case for a far more dynamic early solar system—one where a missing ice giant may have left a lasting imprint on the worlds we see today.
Study Details
Matthew S. Clement et al, The fragility of the Uranian moons during the giant planet instability, Icarus (2026). DOI: 10.1016/j.icarus.2026.117056. On arXiv: DOI: 10.48550/arxiv.2603.21750
