A new study suggests that a planet-sized object may have passed through our solar system around 4 billion years ago, altering the orbits of the four outer planets—Jupiter, Saturn, Uranus, and Neptune.

This flyby could explain why their orbits are slightly tilted and elliptical.

Using computer simulations, researchers found that objects ranging from two to 50 times the mass of Jupiter could have caused these changes, with one scenario involving an object eight times Jupiter’s mass passing as close as 1.69 AU to the sun, Live Science has reported.

This research proposes that such flybys by substellar objects, which are more common than star encounters, may have been frequent enough to shape our solar system’s current configuration.

Written by B.C. Begley