Jupiter has the shortest day of all the planets in the Solar System.
A Jovian day, measured by Jupiter’s rotation on its axis, lasts roughly 9 hours 56 minutes, although the exact value depends on which part of the planet is being tracked. Jupiter is a gas giant rather than a solid world, so its atmosphere rotates at different speeds: equatorial regions complete a rotation faster than higher-latitude regions.
That rapid spin produces a conspicuous equatorial bulge. Jupiter’s equatorial radius is about 7% greater than its polar radius, giving the planet a visibly flattened shape in telescopic images. The rotation also helps organize its atmosphere into alternating bands of clouds and powerful jet streams.
Saturn is sometimes mistaken for the record-holder because it is also a rapidly rotating giant planet, but Jupiter spins faster. Mercury has an especially long solar day because of its slow rotation and orbit, while Neptune’s day is shorter than Earth’s but still longer than Jupiter’s. Jupiter’s fast rotation is remarkable given that the planet is more than 11 times Earth’s diameter.