All planets and moons spin due to the conservation of angular momentum. When a cloud of gas and dust collapses to form a planet or moon, it starts to rotate. This rotation is caused by the random motions of the particles in the cloud. As the cloud collapses, these random motions become more organized and the rotation of the cloud increases.

Once the planet or moon has formed, it continues to spin due to the conservation of angular momentum. This means that the total amount of angular momentum of the planet or moon cannot change. If something were to try to stop the planet or moon from spinning, it would have to exert a torque that is greater than the planet's or moon's angular momentum. This would be very difficult to do.

The only thing that can stop a planet or moon from spinning is tidal friction. Tidal friction is the force that is created when a planet or moon's gravity pulls on the oceans or other bodies of water on its surface. This force can slow down the planet's or moon's rotation. However, tidal friction is a very slow process. It would take billions of years for tidal friction to stop a planet or moon from spinning.

So, all planets and moons spin because of the conservation of angular momentum. This rotation is caused by the random motions of the particles in the cloud that formed the planet or moon. Once the planet or moon has formed, it continues to spin due to the conservation of angular momentum.