Brightness variations of Jupiter's moons as they orbit the planet indicate that the relation between the spin around their axes and their orbital motions is that these moons
A) do not rotate at all while orbiting the planet.
B) rotate exactly once per orbital period.
C) rotate in a way that is controlled by the gravitational influence of the Sun, keeping one face toward the Sun to produce the observed brightness variations.
D) rotate on their axes independently of their orbital motion.

Question

Quizplus · Accepted Answer

Jupiter's moons exhibit synchronous rotation, meaning they rotate on their axes exactly once for each orbit around Jupiter. This keeps one hemisphere of the moon facing Jupiter at all times, similar to how the Moon behaves with Earth. This synchronous rotation, not the influence of the Sun, explains the observed brightness variations as different faces of the moons become visible from Earth during their orbits.

Brightness Variations of Jupiter's Moons as They Orbit the Planet