The Solar System: the Sun, planets, moons, dwarf planets, asteroids and comets, the order of the planets, and how models of the Solar System changed over time.

What this dot point is asking

Edexcel statements 7.2 to 7.4 (separate physics) want you to recall what our Solar System consists of, the names and order of the eight planets in terms of their distance from the Sun, and to describe how ideas about the structure of the Solar System have changed over time.

What the Solar System contains

The Sun is by far the largest object and contains most of the Solar System's mass; its gravity holds everything else in orbit. The planets are large bodies orbiting the Sun, moons orbit the planets, and the smaller bodies (dwarf planets, asteroids and comets) make up the rest. A complete answer names the Sun, the planets and their moons, and the smaller objects.

The order of the planets

A mnemonic such as "My Very Easy Method Just Speeds Up Naming" helps you recall the order. Note that Pluto is no longer counted as one of the eight planets; it is classed as a dwarf planet. The inner rocky planets are closer together than the widely spaced outer giants.

Changing models of the Solar System

Ideas changed as observations improved, particularly with the invention of the telescope, which provided evidence (such as the moons of Jupiter and the phases of Venus) that fitted a Sun-centred model. This is a good example of how scientific models are revised when new evidence does not fit the old idea, a theme that returns with the Big Bang theory.

How Edexcel examines this

These statements are separate-physics only and are examined on both tiers within that route, usually as short recall and description questions. A common item asks you to describe what the Solar System consists of, where the mark scheme rewards the Sun as the central star, the eight planets and their moons, and the smaller bodies (dwarf planets, asteroids, comets); listing only planets is incomplete. You may be asked to name the planets in order from the Sun, where a mnemonic prevents errors and Pluto must not be included. The changing-models question rewards describing the geocentric (Earth-centred) and heliocentric (Sun-centred) models and explaining that improved evidence (such as telescope observations) led to the shift to the heliocentric model. Examiners value this as an example of how scientific ideas change with evidence, so framing it that way strengthens an answer. Keep the geocentric and heliocentric labels straight, as swapping them is the most common error.

Try this

Q1. Name the eight planets in order from the Sun. [2 marks]

• Cue. Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune.

Q2. State which model of the Solar System is accepted today. [1 mark]

• Cue. The heliocentric (Sun-centred) model.