The Moon's internal structure compared with the Earth's, the differences between the near and far sides, how the far side was mapped, escape velocity, and the theories of the Moon's origin.

What this dot point is asking

Edexcel statements 9.1 to 9.5 want you to understand the Moon's major internal divisions compared with the Earth's, the major differences between the appearance of the near and far sides, how information about the far side was gathered, that a spacecraft must reach escape velocity (which only rockets can supply), and the Giant Impact Hypothesis and alternative theories of the Moon's origin.

The Moon's internal structure

The comparison the exam wants is structural: same broad layering, but a proportionally tiny core and a thick crust, reflecting the Moon's smaller size and different history. The small core is one reason the Moon has essentially no global magnetic field today. This internal picture comes from seismometers left by the Apollo missions and from spacecraft measurements.

The near and far sides

The striking near/far difference (lots of maria on the near side, almost none on the far side) is thought to result from the thinner near-side crust letting lava flood the basins more easily. The key examinable points are the visual differences and that the far side was mapped by spacecraft because synchronous rotation hides it. This connects directly to the synchronous orbit (Topic 2) and to space probes (Topic 11).

Escape velocity and reaching the Moon

Escape velocity is why crewed lunar missions need enormous multi-stage rockets: nothing else can provide the energy to break free of the Earth's gravity. The same point recurs for sending space probes anywhere beyond Earth orbit (Topic 11). You are not asked to calculate escape velocity, only to understand the need for it and that rockets are the only means to achieve it.

Theories of the Moon's origin

The Giant Impact Hypothesis is preferred because it best explains the evidence, such as the Moon's small iron core (the impactor's iron stayed with the Earth) and the similarity of Earth and Moon rocks. Capture struggles to explain how the Earth could slow and trap a passing Moon; Co-accretion struggles to explain the Moon's small core. Knowing all three theories, with the Giant Impact as the leading one, is what statement 9.5 requires.

How Edexcel examines this

This is telescopic Paper 2 content with description and explanation marks. The near/far question rewards two valid differences (the far side has fewer maria and is more cratered, with a thicker crust) and the explanation that synchronous rotation hides the far side, which spacecraft then photographed. The structure question rewards comparing the Moon's layers with the Earth's (smaller core, thicker crust). The origin question rewards describing the Giant Impact Hypothesis (Mars-sized impactor, debris accreting into the Moon) and naming an alternative (Capture or Co-accretion), ideally noting the Giant Impact is favoured. Escape velocity is tested as the reason rockets are needed. Synoptic links run to the synchronous orbit (Topic 2), space probes (Topic 11) and planet formation (Topic 12). The biggest error is calling the far side the "dark side", so stress it is hidden, not unlit.

Try this

Q1. State one way the far side of the Moon differs from the near side. [1 mark]

• Cue. It has far fewer maria, so it is more heavily cratered (or its crust is thicker).

Q2. State the currently favoured theory for the origin of the Moon. [1 mark]

• Cue. The Giant Impact Hypothesis (a Mars-sized body hit the early Earth; the debris formed the Moon).