Planetary scientist James O’Donoghue has put together a neat animation of the tilts and spin rates of the Solar System planets. Click on his Tweet to see the animation, or see the the higher-resolution version here.

The animation shows graphically that the simplistic idea that planets form in an orderly fashion from a proto-planetary disc cannot be entirely right. Uranus is tilted over; Venus spins backwards, rather slowly. Why? There must have been collisions, near collisions, and planets perturbing the orbits of other planets early on in our Solar System’s history. Thus we expect that the same thing will have occurred in the exoplanetary systems that we are now finding.