The moons of Jupiter and Uranus are likely 'replacements' because the first ones were destroyed when the planets moved.
March 24, 2026
Original Paper
The fragility of the Uranian moons during the giant planet instability
arXiv · 2603.21750
The Takeaway
Early in our solar system's history, the giant planets likely engaged in a chaotic game of "musical chairs," moving across vast distances. This research shows that these movements were so violent they had an 85% chance of wiping out any moons the planets originally had, meaning our current moons are likely the survivors of a massive cosmic reset.
From the abstract
It is thought that, sometime after their formation, the solar system's giant planets experienced a dynamical instability that caused their orbits to excite, diverge, and ejected one or more objects with masses comparable to the ice giants. A key feature of this model is that the planets experience encounters with other planetary bodies, and these encounters facilitate the capture of nearby small bodies as irregular satellites. Instability simulations indicate that planet-planet encounter distanc