Io is a moon of which planet?

• A. Saturn
• B. Jupiter
• C. Mars
• D. Neptune

Answer: (B)

Io is a moon that orbits Jupiter, the giant planet at the center of our solar system. It’s one of the four Galilean moons—Europa, Ganymede, and Callisto are the others—that Galileo discovered in 1610. Io’s surface is renowned for extreme volcanic activity, driven by tidal heating from Jupiter’s strong gravity and interactions with neighboring moons. Saturn has its own system of moons, Mars has two moons (Phobos and Deimos), and Neptune’s moons orbit Neptune, not Jupiter. So Io belongs to Jupiter.