Planets turn, or rotate, due to a phenomenon called conservation of angular momentum. This is a fundamental principle in physics that states that the total angular momentum of a closed system remains constant.

Here's a breakdown of how it applies to planets:

* Formation: Planets form from swirling clouds of gas and dust called nebulae. These nebulae have a slight, inherent spin. As the material collapses under gravity to form a planet, the spin accelerates. This is because the collapsing material gets closer to the center, meaning it needs to spin faster to conserve angular momentum.

* Conservation: Once the planet forms, it continues spinning at a relatively constant rate. This is because there's no external force acting on it to significantly change its spin. Think of a figure skater spinning with their arms outstretched. When they bring their arms closer to their body, they spin faster to conserve their angular momentum.

* Slight Variations: Over time, the planet's spin can be affected by:

* Tidal forces: The gravitational pull of a nearby star or moon can slow down a planet's rotation. This is why Earth's rotation is gradually slowing down due to the Moon.

* Internal processes: Processes within the planet, like the movement of its mantle, can slightly influence its rotation.

So, in essence, planets turn because they inherited a spin from the nebula they formed from, and this spin is conserved due to the fundamental laws of physics.