Two Lost Ice Giants May Have Shaped the Early Solar System

A new study based on 122 simulations suggests the early outer solar system may have hosted two additional ice-giant planets with masses between Earth and Neptune that were later ejected. Depending on whether the system started with five or six giants, Jupiter’s moons remained stable in the presence of two extra ice giants, while Uranus’s moons stayed stable with only one extra; Miranda’s ice content hints at past moon collisions. The findings imply a far bardziej crowded infancy for the solar system than previously thought, and the team notes further simulations are needed to pin down the exact number and masses of the missing planets. The work was published online in Icarus (2026).