National Geographic has really cool tool you can use to “create your own solar system” – it’s a lot harder than it looks!
You start with a star, and add planets (hint: the little tag attached to your planet gives it a starting direction towards the tag, and a relative velocity proportional to the distance the tag is from the planet – think of it like a rubber ‘leash’). Press “play” and see how long it lasts.
Unfortunately, there’s a catch: occasional planet-sized wanderers sail in from outside of view (much like comets and rogue asteroids do in our own solar system) and crash into your planets, destroying the smaller ones if they hit them. As well, planets that pass too close to one another relative to their sizes can either collide or swing one or the other out of the system.
Very cool – give it a try! None of my little planets live past about 40,000 years, but I’ve got a lone giant still cruising in a stable orbit after almost 200,000 …still waiting to see if something kills it ).