engineering

Internal structure of the Moon

Internal structure of the Moon is a engineering topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Internal structure of the Moon rather than just read about it. In short: Having a mean density of 3,346.4 kg/m3, the Moon is a differentiated body, being composed of a geochemically distinct crust, mantle, and planetary core. This structure is believed to have resulted from the fractional crystallization of a magma ocean shortly after its formation about 4.5 billion years ago.

Key takeaways

Internal structure of the Moon belongs to engineering; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Internal structure of the Moon to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Internal structure of the Moon from memory before moving on to harder problems.

Reference excerpt

Having a mean density of 3,346.4 kg/m3, the Moon is a differentiated body, being composed of a geochemically distinct crust, mantle, and planetary core. This structure is believed to have resulted from the fractional crystallization of a magma ocean shortly after its formation about 4.5 billion years ago. The energy required to melt the outer portion of the Moon is commonly attributed to a giant impact event that is postulated to have formed the Earth-Moon system, and the subsequent reaccretion of material in Earth orbit. Crystallization of this magma ocean would have given rise to a mafic mantle and a plagioclase-rich crust. Geochemical mapping from orbit implies that the crust of the Moon is largely anorthositic in composition, consistent with the magma ocean hypothesis. In terms of elements, the lunar crust is composed primarily of oxygen, silicon, magnesium, iron, calcium, and aluminium, but important minor and trace elements such as titanium, uranium, thorium, potassium, sulphur, manganese, chromium, and hydrogen are present as well. Based on geophysical techniques, the crust is estimated to be on average about 50 km thick. Partial melting within the mantle of the Moon gave rise to the eruption of mare basalts on the lunar surface. Analyses of these basalts indicate that the mantle is composed predominantly of the minerals olivine, orthopyroxene and clinopyroxene, and that the lunar mantle is more iron-rich than that of the Earth. Some lunar basalts contain high abundances of titanium (present in the mineral ilmenite), suggesting that the mantle is highly heterogeneous in composition. Moonquakes have been found to occur deep within the mantle of the Moon about 1,000 km below the surface. These occur with monthly periodicities and are related to tidal stresses caused by the eccentric orbit of the Moon about the Earth. A few shallow moonquakes with hypocenters located about 100 km below the surface have also been detected, but these occur more infrequently and appear to be unrelated to the lunar tides.

Core

Several lines of evidence imply that the lunar core is small, with a radius of about 350 km or less. The diameter of the lunar core is only about 20% the diameter of the Moon itself, in contrast to about 50% as is the case for most other terrestrial bodies. The composition of the lunar core is not well constrained, but most believe that it is composed of metallic iron alloy with a small amount of sulfur and nickel. Analyses of the Moon's time-variable rotations indicate that the core is at least partly molten. Within the giant-impact formation scenario, the core formation of Moon could have occurred within the initial 100–1000 years from the commencement of its accretion from its moonlets. In 2010, a reanalysis of the old Apollo seismic data on the deep moonquakes using modern processing methods confirmed that the Moon has an iron rich core with a radius of 330 ± 20 km. The same reanalysis established that the solid inner core made of pure iron has a radius of 240 ± 10 km. The core is surrounded by the partially (10 to 30%) melted layer of the lower mantle with a radius of 480 ± 20 km (thickness ~150 km). These results imply that 40% of the core by volume has solidified. The density of the liquid outer core is about 5 g/cm3 and it could contain as much as 6% sulfur by weight. The temperature in the core is probably about 1600–1700 K (1330–1430 °C).

In 2019, a reanalysis of nearly 50 years of data collected from the Lunar Laser Ranging experiment with lunar gravity field data from the GRAIL mission, shows that for a relaxed lunar fluid core with non-hydrostatic lithospheres, the core flattening is determined as (2.2±0.6)×10−4 with the radii of its core-mantle boundary as 381±12 km.

Illustrations

Worked examples

Example 1 — a first encounter with Internal structure of the Moon

Start with the simplest possible case. Write down what Internal structure of the Moon claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Internal structure of the Moon before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Internal structure of the Moon ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Internal structure of the Moon

In research: Internal structure of the Moon appears in engineering research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Internal structure of the Moon in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Internal structure of the Moon is common in secondary-school and first-year university syllabi. It links to neighbouring topics Geology of the Moon, so understanding it makes those chapters shorter.
In everyday life: Look for Internal structure of the Moon outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Internal structure of the Moon in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Internal structure of the Moon means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Internal structure of the Moon out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Internal structure of the Moon in simple terms?

Why does Internal structure of the Moon matter?

Because it connects several engineering ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Internal structure of the Moon?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Internal structure of the Moon.