What Is the Moon Made Of? Kaleidoscopic Map Sheds Light

By: Jesslyn Shields & Yara Simón  | 
moon geology
This map of the moon is the most comprehensive geologic map of the lunar surface (nearside shown left, farside shown right). Different surface features, such as lunar highlands (dark earth tones) and ancient lava flows (reds and purples), are designated in different colors. GSFC/NASA, USGS

As the moon orbits Earth, you might not think it has a violent history. However, the leading theory is that it was the offspring of a gnarly collision between baby Earth and a roughly Mars-sized rock we call Theia. The moon's formation, the theory suggests, is due to the magma and rubble ejected into the atmosphere around Earth after this impact.

This all would have gone down around 4.5 billion years ago, and since the moon formed, the heat of the early Earth would have baked it and asteroids would have relentlessly pelted it.


But what is the moon made of? Well, initially, it started off in a molten state (think magma ocean), which solidified over the course of 100 million years, and eventually formed the moon's crust. This is all to say, the serene, white orb in the night sky belies how much action she's really seen.

With the Unified Geologic Map of the Moon, a collaboration between the USGS Astrogeology Science Center, NASA and the Lunar Planetary Institute, you can see the moon for the war hero she actually is.


What Is the Unified Geologic Map of the Moon's Surface?

This digital map is the most detailed geological map of the moon, compiled from data collected starting with the Apollo missions more than 50 years ago. Created using six Apollo-era moons combined with more recent satellite data, the map features a kaleidoscopic matrix of geologic formations from different eras of the moon's history, detailing the types and ages of rock found on the moon's surface.

It's unbelievably detailed: For every 1 millimeter (0.04 inches) presented on the map, astronauts can traverse the geology of 5 kilometers (3.1 miles) for future lunar exploration.


"This map is a culmination of a decades-long project," said Corey Fortezzo, USGS geologist and lead author, in a press release. "It provides vital information for new scientific studies by connecting the exploration of specific sites on the moon with the rest of the lunar surface."

Its creators wanted the moon map to benefit everybody, from students to aspiring astronauts. You can download the map here.


The Lunar Surface

Since the moon is susceptible to comet, meteoroid and asteroid impacts, there are numerous craters on the surface. The Earth's moon is mostly gray and dusty, with lunar soil, called "regolith," appearing as rocky remnants.

The moon is also marked by stark contrasts: the dark areas known as maria and the lighter, rugged highlands. Once filled with lava, the maria are volcanic plains made up mostly of basalt, an igneous rock. In contrast, the highlands are heavily cratered terrains composed of older crust material. There is also water on the moon, though it's nowhere near as abundant as what appears on the Earth's surface.


And you will see a few familiar items on the surface as well. The lunar surface provided the backdrop for the Apollo moon landings, which gave humanity a close-up look at its features. As astronauts, like Neil Armstrong, took lunar samples home to get a better understanding of the moon's composition, they also left a few things behind, such as equipment, a U.S. flag and a camera.

What's in a Name?

Whether you know her by "the Moon," "Luna" or "Lune," Earth's moon does not have a snazzy name. However, this isn't the case for other moons. Currently, scientists first identify moons through a number before giving them an official name, inspired by mythological and literary characters (like Bergelmir or Ophelia) from different cultures.


The Lunar Crust

The outermost layer of the moon's solid surface is the lunar crust. It varies in thickness and composition in different regions of the Moon: about 43 miles (70 kilometers) thick on the near side and 93 miles (150 kilometers) on the far side.

Earth's crust is, on average, about 19 miles deep. Oxygen, calcium, aluminum, hydrogen, potassium, silicon, iron, uranium, magnesium, small bits of titanium and thorium make up the crust.


The Farside of the Moon

You can only see the near side of the moon from Earth. If you want to see the farside of the moon, you'd have to travel to space. What would you see? A lack of marias but lots of craters.


The Lunar Mantle

Part of the moon's internal structure, the mantle lies beneath the crust and extends toward its core. Though not as well documented as Earth's mantle, the lunar mantle is likely composed of olivine and pyroxene (made up of oxygen atoms, iron, silicon and magnesium). At about 838 miles (1350 kilometers), the mantle is also much thicker than the crust.


The Lunar Core

The moon's core is the central, innermost layer of the Moon's interior. With an iron-rich core, it is similar to the Earth's core — though not exactly the same. The lunar core stands out because of the partially molten layer that surrounds it. It is also proportionately smaller — making up 20 percent of the total diameter — than the core of the Earth or other planets.

This article was updated in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.