Describe the Solar System as containing: (a) one star, the Sun (b) the eight named planets and know their order from the Sun (c) minor planets that orbit the Sun, including dwarf planets such as Pluto and asteroids in the asteroid belt (d) moons, tha

Published by Patrick Mutisya · 8 days ago

IGCSE Physics 0625 – Topic 6.1.2 The Solar System

6.1.2 The Solar System

The Solar System is the collection of bodies that are bound by the Sun’s gravity. It consists of a single star, eight major planets, a variety of smaller bodies and many natural satellites (moons).

1. The Sun – our star

The Sun is a G‑type main‑sequence star that provides the heat and light necessary for life on Earth. It contains about 99.9 % of the total mass of the Solar System.

2. The eight named planets

Planets are large bodies that orbit the Sun, are massive enough for their self‑gravity to make them nearly round, and have cleared their orbital neighbourhood of other debris.

Suggested diagram: A schematic view of the Solar System showing the Sun, the eight planets in order, the asteroid belt, and the orbits of dwarf planets.

  1. Mercury

  2. Venus

  3. Earth

  4. Mars

  5. Jupiter

  6. Saturn

  7. Uranus

  8. Neptune

OrderPlanetTypeMean distance from Sun (AU)Key feature
1MercuryTerrestrial0.39Smallest, no atmosphere
2VenusTerrestrial0.72Thick CO₂ atmosphere, runaway greenhouse
3EarthTerrestrial1.00Only known planet with liquid water
4MarsTerrestrial1.52Red surface, thin CO₂ atmosphere
5JupiterGas giant5.20Largest planet, strong magnetic field
6SaturnGas giant9.58Prominent ring system
7UranusIce giant19.2Rotates on its side
8NeptuneIce giant30.1Strong winds, blue colour

3. Minor planets and dwarf planets

Minor planets are bodies that orbit the Sun but are not large enough to be classified as planets. Dwarf planets are a subset of minor planets that are massive enough to be round but have not cleared their orbital zone.

  • Pluto – dwarf planet in the Kuiper Belt; orbital period ≈ \$248\$ years.

  • Eris, Haumea, Makemake – other recognised dwarf planets.

  • Asteroids – rocky bodies mainly found in the asteroid belt between Mars and Jupiter.

4. Moons (natural satellites)

Moons are bodies that orbit planets. They vary widely in size, composition and geological activity.

  • Earth’s Moon – the only permanent natural satellite of Earth.

  • Jupiter’s four largest moons (the Galilean moons): Io, Europa, Ganymede, Callisto.

  • Saturn’s largest moon: Titan, which has a dense nitrogen atmosphere.

  • Uranus and Neptune each have several notable moons (e.g., Triton around Neptune).

5. Smaller Solar System bodies

These include comets, meteoroids and other transient objects.

  • Comets – icy bodies that develop a coma and tail when they approach the Sun. Their orbits are typically highly elliptical.

  • Meteoroids – small fragments of rock or metal; when they enter Earth’s atmosphere they become meteors, and if they reach the ground they are called meteorites.

Summary

The Solar System is a hierarchical system:

  1. One star – the Sun.

  2. Eight planets in order from the Sun.

  3. Minor planets, including dwarf planets (e.g., Pluto) and the asteroid belt.

  4. Moons that orbit the planets.

  5. Smaller bodies such as comets and meteoroids.