the Moon terrain

Is the Moon just a rock? Exploring The Moon's Complex Makeup

Last Updated: February 10, 2023

The Moon is the easiest body in our solar system to observe with the naked-eyed, but you may wonder about the dark and light spots on the surface. So what causes these strange features, and what makes up our nearest neighbor? 

In this article, we will explore the scientific findings and theories surrounding the Moon, with a focus on its surface features and composition. From the impact craters and vast plains to the lunar rocks and soil, we will uncover the facts that make the Moon more than just a rocky satellite of Earth.

The Moon's Composition

Like many planets in the Milky Way, such as Venus, Mercury, and Mars, the Moon is a rocky body with a combination of metallic substances found within the layers of its surface. Although the Moon is mainly made of iron, other metals can be found on the Moon, including aluminum, magnesium, titanium, silicon, silver, gold, and mercury.

As the Moon formed, heavier materials sunk into the core while lighter materials stayed in the outer layers called the crusts. As a result, the Moon is made up of different layers, each with its own unique composition. Scientists have used various methods, like measuring earthquakes and the Moon’s spin and gravity, to figure out what’s inside. 

The core of the Moon is its densest layer, mostly made of iron and nickel, with a solid inner core of 480 km diameter and a fluid outer core of 660 km diameter. 

The mantle and crust, also known as the lithosphere, make up the rest of the Moon, with the mantle being roughly 1350 km thick and the crust around 50 km. It is believed that the Moon was once a great ocean of magma, with dense minerals sinking to the bottom and lighter minerals rising to the surface to form the crust. 

The thickness of the crust varies, with the side facing Earth being thinner and the side facing away being thicker, which researchers are still trying to understand.

The regolith makes up the outermost layer of the Moon and is almost like moon dust. Just like the dust on Earth, regolith is soft and easily compressed to leave the shape of any item that impacts the surface. Such impacts are seen as impact craters whenever celestial bodies hit the Moon or in perfectly preserved footprints from the astronauts. This layer can be up to about 65 feet deep.

cratered lunar surface

The lunar surface is really soft and anything touching it will leave a mark.

How Can We Tell What the Moon is Made of?

During the Apollo missions, the astronauts weren’t just traveling to the Moon. They also conducted experiments on the Moon’s surface and while in orbit. The experiments in orbit have helped determine the composition of the lunar surface, but it required special tools.

For example, Apollo 15, 16, and 17 held a scientific instrument module (SIM) bay in the Service Module. A series of experiments took place, including a spacewalk to recover film from a 24-inch panoramic camera (used to take high-resolution images of the lunar surface) or a command module pilot partaking in a deep space extra-vehicular activity.

During the Apollo 15, eight tools were used, such as:

  • X-ray fluorescence spectrometer: done to measure the composition of the lunar surface from orbit, but it also analyzed the sunlit portion of the Moon under the spacecraft.
  • Gamma-ray spectrometer: measured the chemical composition of the lunar surface in conjunction with alpha and X-ray particles to create a map of the composition of the lunar surface ground track.
  • Alpha-particle spectrometer.
  • 3-ich mapping camera.
  • Laser altimeter.
  • Mass spectrometer.
  • Lunar sounder.
  • Subsatellite.

During Apollo 16, eight more similar experiments were conducted. However, for the Apollo 17 mission, three new tools were used to carry out experiments in the SIM bay, including:

  • Lunar sounder.
  • Infrared scanning radiometer – to measure lunar nighttime temperatures and cooling rates.
  • Far-ultraviolet spectrometer.

Undoubtedly, the Apollo landings changed everything. The missions have provided precious data on what lies beneath by installing various devices that could listen to natural tremors shuddering through the Moon. When the Apollo astronauts returned home with their treasures, chemists, and scientists could start investigating our satellite’s composition directly.

This research continues as new analytical techniques are developed, and theoretical questions are posed. Even today, these data are helping scientists gain a greater understanding of what the Moon is made of, inching us closer to solving the mystery of how it formed.

There are several other ways that scientists have used over the years to determine what the Moon is made of:

  1. Sampling: Another way that scientists have determined the composition of the Moon is through the analysis of lunar samples brought back to Earth during the Apollo missions. These samples, which include rock, soil, and dust, have been studied in detail and provide a wealth of information about the Moon’s history and composition.

  2. Spectroscopic Analysis: This technique involves analyzing the light reflected off the Moon’s surface to determine its chemical makeup. By looking at the specific wavelengths of light that are absorbed or reflected, scientists can determine the presence of specific elements and minerals on the Moon.

moon composition by layer

A diagram showing the different layers that makes up the Moon. Credit: Kelvinsong

The Moon's Formation and History

There are three ways that moons are believed to have formed. According to scientists, some planets sucked wandering planetesimals into orbit as they passed close by. For example, Deimos and Phobos formed elsewhere in the solar system before Mars captured them.

This might explain why the Moon and Earth have different ingredients. However, most moons captured by their parent planets in such a way are oddly shaped and have wonky orbits. Because our Moon is round, it probably was not a passing stranger snared by the Earth’s gravity.

Another idea is that the Moon and Earth formed together about the same time. Jupiter’s moons, such as Europa, Io, and Ganymede, are thought to have been formed out of the crumbs left by Jupiter’s creation. However, the issue for our Moon is that it is metal-poor, while the Earth is metal-rich, so how could they form from the same material?

Finally, scientists believe that the Moon had a much more violent birth. They theorize that a Mars-sized object they named Theia smashed into the young Earth. The impact has spewed chunks of the Earth’s crust into space, some debris bounding together what was left of Theia’s core to from the Moon as we know it today. However, conclusive proof for this idea still needs to be provided.


To our eyes, the Moon is the most significant and brightest object in the night sky, yet when compared to Jupiter, it’s an astronomical pipsqueak. The Moon is a ball of rock about 3,474 km  / 2,200 mi in diameter, a bit more than a quarter the size of Earth, with no atmosphere to speak of, so there’s no weather.

Geologically speaking, it’s all but dead, with only an occasional jostle from within. Quakes that occur on the Moon are known as moonquakes. When we compare our Moon to the rest of the Solar System, it is the fifth largest satellite.  Even though much has already been learned about the Moon’s composition, further studies will surely surprise the next generation of explorers even more.


Written by Hrenciuc Daniel

Hello, my name is Daniel and I am a space enthusiast. I love everything related to space and SCFI, and although I like both Star Wars and Star Trek, I believe we will find something entirely different out there. I am an astronomy writer with a passion for both history and mythology. Each star has its tale. Let me tell you their story!

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