Sedna Flyby Animation

This animation sequence follows the evolution of 20,000 planets in orbit around two stars. Our goal is to produce objects with highly elongated orbits like Sedna's. Click here to see the animation.


Starting Point

The bright yellow dots indicate the positions of two solar-type stars. Each star is surrounded by a swarm of planets orbiting at distances of 30-80 AU from the star. All of the planets orbit their parent star in the same orbital plane, as in the rings of Saturn. When Saturn's rings are seen edge-on, they are almost invisible. Viewed edge-on, the ring of planets orbiting each star in the simulation are also barely visible.

Interaction Begins

Initially, each swarm of planets feels only the gravity from its parent star. The other star is too far away to feel the pull from its gravity. But, as the two stars move closer together, the pull of gravity from the other star increases. When the magenta swarm passes over the cyan swarm, each swarm begins to feel the gravity from the other star. The extra pull of gravity from the passing star distorts the nice, circular pattern of the original orbits.

Distorted Orbits

As the animation continues, planets at the inner edge of the swarm continue to move in roughly circular orbits around their parent star. Farther out, the orbits become more and more distorted.

In some places, the gravity from the two stars compresses the orbits. Bright rings form where planets are pushed into orbits that are closer together.


In other places, the gravity of the passing star overwhelms the gravity of the parent star, pulling the planet away. The passing star captures a few of these planets. Sometimes, though, the gravity of the parent star is just strong enough to keep the planet. These planets end up on highly elongated orbits.

Click here to see the animation.

After the encounter, a mixture of magenta and cyan planets orbits each star. The magenta and cyan planets lie in distinct rings and bands. Over time, gravity from other planets in the Solar System, like Neptune, will smooth out the bands. However, the highly elongated orbits - including orbits that resemble Sedna's - remain.