Early Solar System May Have Lost Two Giant Planets

Scientists suggest a new computational model showing the early solar system may have lost two gas giant planets billions of years ago ^[1].

This finding provides a potential explanation for some of the most enduring mysteries of our planetary neighborhood. Specifically, it addresses why Uranus possesses such an extreme axial tilt and why its moons follow irregular orbits.

The study proposes that the early solar system contained five or six gas giants rather than the four present today ^[1]. According to the researchers, a period of dynamical instability occurred during the system's formation. This gravitational chaos likely led to the ejection of two planets [1, 2], sending them drifting into interstellar space.

This instability would have exerted massive gravitational forces on the remaining bodies. Scientists said this process likely knocked Uranus off its original orientation — resulting in the planet rotating on its side — and disrupted the orbits of its surrounding moons [1, 3].

While the current solar system is relatively stable, these calculations suggest a violent history. The loss of these two bodies represents a significant shift in the mass and architecture of the early system ^[1]. The researchers used computer-based calculations to simulate these interactions and determine how the ejection of these planets would influence the remaining orbits [1, 4].

These findings challenge simpler models of planetary formation. By accounting for the missing mass of two ejected giants, the model better aligns with the observed anomalies of the outer planets [1, 2].