The Hilda family of asteroids is in a 3:2 orbital resonance with which planet?

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

Answer: (A)

This question hinges on orbital resonances with a planet. The Hilda asteroids are in a 3:2 mean-motion resonance with Jupiter, meaning they complete three orbits around the Sun for every two orbits Jupiter completes. Since Jupiter's orbital period is about 11.86 years, the Hildas spend roughly 7.9 years per orbit, so three of their orbits line up in the same time it takes Jupiter to complete two. This precise timing keeps their gravitational interactions repeating in a stable pattern, locking them into a distinctive group near Jupiter’s orbit just outside the main belt.

The other planets don’t form this 3:2 resonance with the Hildas because their orbital periods don’t line up in that same ratio, so they don’t create the same regular, stabilizing gravitational influence.