Why does a planet move faster when it is closer to the Sun?

A planet moves faster when it is closer to the Sun because of Kepler’s second law of planetary motion, which states that a radius vector joining a planet to the Sun sweeps out equal areas in equal lengths of time.12

Because the planet follows an elliptical orbit with the Sun at one focus, its distance from the Sun changes throughout its revolution. To ensure that the area swept out by the radius vector remains constant over equal time intervals, the planet must travel with a higher velocity when it is near perihelion (its closest point to the Sun) and a lower velocity when it is near aphelion (its farthest point).132

This phenomenon is a direct consequence of the conservation of angular momentum, as the gravitational force exerted by the Sun acts along the radius vector and does not exert a torque that would change the planet's angular momentum.24