The Solar System and Formation of Stars — AQA GCSE Physics (Separate)
The Sun and the rest of the solar system formed from a cloud of gas and dust, pulled together by gravity.
Formation of the Sun and solar system
The solar system formed from a nebula — a cloud of dust and gas:
- Gravity pulled the cloud together.
- As it collapsed, it became hotter and denser, forming a protostar at the centre.
- When the core became hot and dense enough, nuclear fusion began, and the Sun (a main sequence star) was formed.
- The remaining dust and gas formed the planets, moons and other objects orbiting the Sun.
The structure of the solar system
- The Sun (a star) is at the centre.
- The eight planets orbit the Sun: the four inner rocky planets (Mercury, Venus, Earth, Mars) and the four outer gas/ice giants (Jupiter, Saturn, Uranus, Neptune).
- Dwarf planets (e.g. Pluto), moons, asteroids and comets also orbit the Sun.
The solar system is part of the Milky Way galaxy, which contains billions of stars.
Gravity and orbits
The Sun's gravity keeps the planets in orbit. The planets, in turn, hold their moons in orbit by gravity.
Exam tips
- The Sun formed from a nebula pulled together by gravity → protostar → fusion → star.
- Learn the order of the planets (Mercury → Neptune); inner = rocky, outer = giants.
- The solar system is in the Milky Way galaxy.
- Gravity holds the solar system together.