Why do planets stay in orbit?
Show answer & explanation
Answer: Gravity pulls them inward while they keep moving sideways
Atmosphere creates drag — Wrong. Planets orbit in the vacuum of space, where there is no atmosphere to create drag. Their motion is governed by gravity and inertia, not air resistance.
Space vacuum holds them — Wrong. A vacuum does not hold or pull anything. Orbits arise because gravity pulls planets toward the Sun while their sideways motion keeps them from falling in.
Gravity pulls them inward while they keep moving sideways ✓ — Correct! The Sun's gravity pulls a planet toward it, but the planet's sideways speed keeps it from falling straight in. The result is a curved path around the Sun—a stable orbit.
Go deeper: Kepler's laws of planetary motion · Newton's law of universal gravitation · General relativity
Play today's quiz — new questions dailyMore Astronomy & Space questions
- Which gas escapes fastest from Earth's atmosphere as it slowly leaks to space?
- Why is Earth's day getting slightly longer every century?
- Why was Earth's day stuck at 19.5 hours for 1.5 billion years?
- Why might using several small reactors be better than one giant reactor on the Moon?
- Why is fission likelier than fusion for first Moon bases?
- Why put a lunar reactor away from the habitat?