How fast do planets move around the Sun?

The closer a planet is to the Sun, the faster it must orbit to balance gravity. Mercury is the fastest planet, moving at nearly 48 kilometers per second in its orbit, while Neptune is much slower because it is far away and takes 165 Earth years to complete one trip around the Sun. These orbital speeds are set by gravity and the shape of the planet’s orbit, not by the planet’s size alone. Earth travels at about 29.8 kilometers per second. This is why the inner planets zip around the Sun quickly while the outer planets take much longer.