Which planet has the fastest rotation in the Solar System?

Jupiter has the fastest rotation of any planet in the Solar System, completing a day in about 9 hours 56 minutes.

Jupiter is a gas giant with no solid surface that could define a single universal day. Scientists measure its rotation from radio emissions and the movement of features in its atmosphere. Because the planet rotates different atmospheric bands at different rates, the quoted period is an average standard for the planet’s interior or magnetic field.

Its rapid spin contributes to a pronounced equatorial bulge: Jupiter’s equatorial diameter is substantially greater than its polar diameter. The rotation also helps produce the planet’s banded cloud appearance and powerful jet streams.

Saturn rotates nearly as quickly, but Jupiter remains the fastest-rotating planet. Earth’s rotation takes about 24 hours, making Jupiter’s day less than half as long despite the planet’s much greater size.