A day is defined as how long it takes a planet to rotate once on its axis. A day on Earth is 24 hours long. A day on Saturn lasts 10 hours and 32 minutes. Which of the following best explains the difference between these two planets?

a. Saturn is farther from the sun than Earth is
b. Saturn revolves around the Sun faster than Earth does
c. Saturn's gravitational force is greater than Earth's
d. Saturn rotates on its axis faster than the Earth does