Science
What is a Planet?
A planet is a large, round object that orbits a star, is massive enough for its gravity to pull it into a sphere, and has cleared its orbit of other debris. Earth is a planet, and eight planets orbit our Sun.
See it, don’t just read it.
Watch a 2-minute lesson with voice + animation that explains a planet.
Key things to understand
- 1A planet orbits a star (our planets orbit the Sun), not another planet.
- 2It must be big enough for its own gravity to pull it into a roughly spherical shape.
- 3It must have 'cleared its neighbourhood' — swept up or flung away most other objects in its orbit.
- 4Our solar system has eight planets, from rocky Mercury to the gas giant Jupiter.
- 5Pluto is now classed as a 'dwarf planet' because it hasn't cleared its orbit.
Frequently asked questions
- Why isn't Pluto a planet anymore?
- In 2006 astronomers defined a planet as a body that has 'cleared its orbit' of other debris. Pluto shares its region with many icy objects, so it was reclassified as a dwarf planet.
- How many planets are in the solar system?
- Eight: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto and similar bodies are dwarf planets.
- What's the difference between a planet and a star?
- A star produces its own light and heat through nuclear fusion; a planet doesn't — it only shines by reflecting its star's light, and it orbits the star.