u/Nolencein r/FlutterDev • Recommends
On “Simple app about your own Solar System. Flutter/Dart”
If you don't need any of the planets to be widgets you could use a custom painter and just follow a basic tutorial for rotating objects around a point.
Maybe try this coding train one
It'd be mostly the same stuff except you'd need to animate it differently using setstate or a valuenotifier or something.