The field of celestial mechanics often can feel a bit intimidating, but the two University of Toronto Department of Astronomy & Astrophysics papers discussed in this Now video feel more down-to-Earth than usual.
Whether it's the sumo wrestling analogy of one massive body booting another one, or the croquet-like mental image of one planet knocking another out of the game, it's all pretty easy to visualize.
The studies don't particularly depend on planetary composition. Rather, it's all about mass and gravitational pull. But you can't really refer to our solar system's "four gas giants" without bringing up the whole "ice giant" categorization.
Uranus and Neptune are still essentially gas giants. They're large, and they're certainly not rocky worlds like the inner terrestrial planets. But they're also composed of heavier elements than Saturn and Jupiter, and they owe their formation to differing accretion models.
According to planetologist Mark Hofstadter, oxygen, carbon, nitrogen and sulfur likely became part of Uranus and Neptune as ices and compounds trapped in water ice.
However, you won't find much that resembles ice on either world today. Most H20 on the ice giants probably takes the form of a supercritical fluid [source: Hofstadter].