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# How the Apollo missions transformed our understanding of the Moon’s origin
- URL: https://jatan.space/apollo-moon-origin/
- Published: 2022-09-30T15:18:00.000Z
- Updated: 2026-08-31T11:14:16.000Z
- Description: And what we’re learning as we send missions again to Luna.
- Author: Jatan Mehta
- Tags: Articles

![](https://jatan.space/content/images/2024/02/https-3a-2f-2fbucketeer-e05bbc84-baa3-437e-9518-adb32be77984-s3-amazonaws-com-2fpublic-2fimages-2fd9a8b14c-02a7-4e9e-afad-d8262d8c9198_2500x1600-jpeg.jpg)

Our Moon as seen by the Galileo spacecraft when it flew past on December 7, 1992\. [Image: NASA](https://www.flickr.com/photos/nasacommons/9458193857/)

Where did [our Moon](https://jatan.space/why-explore-the-moon/) come from? The origin of Earth’s cosmic companion is a fundamental question in planetary science. From [Galileo’s first telescopic observations of the Moon](http://galileo.rice.edu/sci/observations/moon.html) to humans walking on its surface, our understanding of its origins has come a long way. Yet it’s far from complete.

Over the decades, scientists have proposed multiple hypotheses to attempt explaining how the Moon came to be. In this article, I focus on the one with the highest consensus among scientists: the Giant Impact Hypothesis (GIH). According to the GIH, a titanic collision took place 4.5 billion years ago, when the planets had just formed in a [still-chaotic Solar System](https://jatan.space/solar-system-history-101/). A young Mars-sized planet, named Theia, collided with the newly born Earth. The blistering impact ejected a colossal amount of material. While some of this material escaped to space, the rest stayed in orbit around Earth and coalesced to form the Moon.

![](https://jatan.space/content/images/2024/02/https-3a-2f-2fbucketeer-e05bbc84-baa3-437e-9518-adb32be77984-s3-amazonaws-com-2fpublic-2fimages-2f4c4b0edd-e2cc-4c93-a253-9b01674da740_1035x620.png)

A simplistic representation of the Giant Impact Hypothesis. Graphic: [Jatan Mehta](https://jatan.space/about); derivative work of Wikipedia user [BedrockPerson](https://commons.wikimedia.org/wiki/File:Bigsplashsimple.png) and released under [CC BY-SA 4.0](https://creativecommons.org/licenses/by-sa/4.0/)

The best evidences for the GIH come from NASA’s [Apollo Moon landings](https://www.planetary.org/space-missions/celebrating-apollo-at-50) between 1969 and 1972, whose [382 kilograms of lunar rock, soil, and core samples](https://www.lpi.usra.edu/lunar/samples/atlas) brought to Earth allowed us to test multiple hypotheses in various ways. [300 grams of samples](https://www.lpi.usra.edu/lunar/samples/#lunas) fetched by the former Soviet Union’s three Luna missions also contributed to our understanding. The picture of the Moon’s formation emerging from Apollo and Luna sample studies has been anything but simple. The results have been difficult to reconcile and interpret for scientists. Here’s a rundown of some key findings, both for and against the GIH.

## Findings in support of the GIH

### Magma ocean

The GIH implies that the newly formed Moon post-Earth-impact must be in a molten state. Scientists have estimated our Moon to have been covered in a vast magma ocean [at least 500 kilometers deep](https://doi.org/10.1016/j.epsl.2011.02.004). Over time, this magma would crystallize to form the Moon’s mantle and crust. During this process, heavier minerals like [olivine](https://en.wikipedia.org/wiki/Olivine) and [pyroxene](https://en.wikipedia.org/wiki/Pyroxene) would’ve sunk to form the mantle. And lower density minerals, principally [plagioclase](https://en.wikipedia.org/wiki/Plagioclase), would float on top and crystallize into light [anorthosite](https://en.wikipedia.org/wiki/Anorthosite)\-based crust, which is what the bright “highland” regions on the Moon we see should be made of.

![](https://jatan.space/content/images/2025/07/magma-ocean-early-moon-illustration.jpg)

Illustration of a young Moon with a global magma ocean and newly forming crust. [Image: CCTV+](https://www.youtube.com/watch?v=d8EfwGxza50)

The GIH further predicts that during this process, any chemically incompatible elements in the magma would get sandwiched between the crust and mantle, forming what is known as [KREEP](https://en.wikipedia.org/wiki/KREEP)\-rich magma. **KREEP** is an acronym built from the letters **K** (Potassium), **REE** (rare-earth elements) and **P** (Phosphorus). KREEP also encompasses [heat-producing and radioactive elements](https://www.planetary.org/articles/3013) such as thorium.

![](https://jatan.space/content/images/2024/02/https-3a-2f-2fbucketeer-e05bbc84-baa3-437e-9518-adb32be77984-s3-amazonaws-com-2fpublic-2fimages-2f839cd6a4-4d99-4eef-90e4-a417666f5fd8_975x389.png)

A simplified illustration of how the Moon’s crust formed. [Graphic: LPI](https://www.lpi.usra.edu/meetings/LEA/presentations/OpeningPlenary/Pieters%5FNAC%5FNRCpresentation.pdf)

The very first lunar samples, [brought to Earth by Apollo 11](https://www.lpi.usra.edu/lunar/missions/apollo/apollo%5F11/samples) contained millimetric fragments from the rocky highlands nearby. These fragments were not only found to be made of anorthosites but had KREEP-rich materials as well, confirming the molten state of the ancient Moon and supporting the GIH. Samples from later Apollo missions and Luna ones [supported](https://www.lpi.usra.edu/lunar/samples/atlas/compendium/Luna20Core.pdf) the hypothesis too.

### The lunar core

Also supporting the GIH were three independent experiments on Apollo missions that provided scientists insights into the Moon’s interior. Data from the [Passive Seismic Experiments](https://web.archive.org/web/20170627080839/https://www.lpi.usra.edu/lunar/missions/apollo/apollo%5F16/experiments/ps/), [Laser Ranging Retroreflectors](https://web.archive.org/web/20160727220755/https://www.lpi.usra.edu/lunar/missions/apollo/apollo%5F15/experiments/lrr), and [Lunar Surface Magnetometers](https://web.archive.org/web/20160306013050/http://www.lpi.usra.edu/lunar/missions/apollo/apollo%5F15/experiments/lsm/) all implied that the Moon’s core shouldn’t be larger than 900 kilometers. That means the lunar core, solid and liquid combined, represents only about 25 percent of the Moon’s radius, in contrast to about 50 percent for other rocky planets like Earth. The GIH predicts that the Earth-Theia collision would result in Theia’s core getting absorbed into Earth, leaving a smaller core mass for the Moon. The calculated sizes of the Moon’s core from these three independent experiments thus agrees with the GIH. It’s also worth noting that Earth is the densest planet in the Solar System, which could be explained by the absorption of Theia’s core.

![](https://jatan.space/content/images/2026/08/moon-earth-composition-comparison.jpeg)

Simplified view of the layers of our Earth’s interior and the Moon’s, and how the proportions of the two are very different. [Image: NASA / Vi Nguyen](https://science.nasa.gov/moon/composition/)

### Volatile depletion

Another area of interest for the GIH is volatiles, which are elements with low boiling points such as nitrogen, water, carbon dioxide, hydrogen and more. Their low boiling points mean their abundances on planetary bodies deplete with time, inversely proportional to factors like the object’s gravity. On the Moon, large scale volatile depletion could’ve been due to two processes happening at different times: first, the evaporation of volatiles when the Moon formed and second, evaporation from ancient volcanism.

Scientists figured that studying [isotopes](https://en.wikipedia.org/wiki/Isotope)—which are different subatomic forms of a given element—in existing lunar volatiles will help us know the Moon’s past. Since isotopes in volatiles deplete differently based on the nature of the event, the kinds we measure can tell us which and how much of the above two processes shaped the Moon of today. For example, lighter isotopes of Zinc would get evaporated in large amounts during the Moon’s fiery formation but remain unaffected by volcanic processes.

Scientists observed in Apollo samples that [lighter isotopes of Zinc are less abundant than the heavier ones](https://doi.org/10.1038/nature11507). This means large amounts of volatiles were indeed lost during the Moon’s formation, supporting the GIH prediction of a fiery formation of Luna from a volatile-rich Earth.

## Findings against the GIH

### Titanium isotopes

If the Moon indeed formed from the collision of two objects as the GIH posits, it should’ve inherited some of its material from Earth and some from Theia. One way to test that is to measure the titanium isotopic composition of the Moon and compare it to Earth’s. If the Moon formed from both Earth’s and Theia’s materials, its titanium signature should be a mix of both. Titanium is a good element to measure because it isn’t easily vaporized and tends to remain solid or molten even at high temperatures. Our Moon’s titanium abundances should thus roughly be in the same state now as during its formation.

[Comparative analysis of titanium in Apollo samples](https://news.uchicago.edu/story/titanium-paternity-test-fingers-earth-moons-sole-parent) indicates that the Moon’s titanium came from Earth alone; it’s not a mix of Earth and Theia. In stark contrast, meteorites found on Earth show large variations in titanium isotopes, indicating their distinct and varied origins. How then could the GIH be correct?

One unlikely explanation is that Theia had the same composition as Earth but that’s a long shot. [Computer simulations of the GIH collision](https://arxiv.org/abs/1012.5323) by Caltech researchers in 2007 estimated the origin of various materials relative to the Sun, and how they would’ve been distributed across the early Solar System. They found the likelihood of Theia naturally having an identical isotopic composition to Earth to be less than 1%. And so for the Moon to have identical titanium signatures as the Earth is an anomaly for the GIH.

On the other hand, scientists proposed in 2021 that the two continent-sized regions discovered in Earth’s mantle with greater density, one beneath Africa and one beneath the Pacific Ocean, [could be Theia’s remains](https://www.hou.usra.edu/meetings/lpsc2021/pdf/1980.pdf). That between Earth and the Moon, the former would’ve absorbed most of Theia’s material not lost to space. In 2022, scientists published a study of six lunar meteorites, which concluded that [the Moon’s noble gases like helium and neon come from Earth](https://ethz.ch/en/news-and-events/eth-news/news/2022/08/one-more-clue-to-the-moons-origin.html) too.

![](https://jatan.space/content/images/2024/02/https-3a-2f-2fbucketeer-e05bbc84-baa3-437e-9518-adb32be77984-s3-amazonaws-com-2fpublic-2fimages-2fdb517b1d-f2df-4f7d-af9a-6fe37751e1ff_1022x246-jpeg.jpg)

Remains of proto-planet Theia may be in Earth’s mantle. [Image: Q. Yuan, et al.](https://www.hou.usra.edu/meetings/lpsc2021/pdf/1980.pdf)

### A shared water source for Earth and Luna

Much like the case with titanium, the isotopic compositions of lunar hydrogen and oxygen can be compared with that of Earth. The volcanic glass samples brought back [from Apollo 15](https://www.lpi.usra.edu/lunar/missions/apollo/apollo%5F15/samples) and [17](https://www.lpi.usra.edu/lunar/missions/apollo/apollo%5F17/samples) had minor quantities of water in them. The isotopic composition of hydrogen in this water [is nearly identical](https://doi.org/10.1126/science.1235142) to that of water in Earth’s mantle. Likewise, the Moon’s oxygen isotopic composition, measured in Apollo 11, 12, 15, 16 and 17 samples, [also show identical natures](https://doi.org/10.1126/science.1063037) to Earth. When [compared to other Solar System objects](http://www.psrd.hawaii.edu/Dec01/Oisotopes.html), such as Mars, the Earth-Moon system is thus compositionally distinct from them and identical to each other, with seemingly no trace of a distinct Theia in Luna.

![](https://jatan.space/content/images/2024/02/https-3a-2f-2fbucketeer-e05bbc84-baa3-437e-9518-adb32be77984-s3-amazonaws-com-2fpublic-2fimages-2f79effce7-b029-447f-9a1a-3dd0fa912cc2_709x567-jpeg.jpg)

Oxygen isotopic composition for the Earth-Moon system and Mars. The Moon’s composition is identical to Earth. [Image: K Pahlevan / D Stevenson / Caltech](https://arxiv.org/pdf/1012.5323.pdf)

In water’s case especially though, a much broader study is necessary because [Apollo landing sites](https://jatan.space/apollo-landing-sites-overview/) represent a small slice of the Moon’s diversity, all being near-equatorial and on the nearside. Scientists studying [lunar water ice](https://jatan.space/ultimate-guide-to-water-on-the-moon/) samples fetched by future missions and [determining the relative contributions of various sources](https://jatan.space/moon-monday-issue-177/#the-search-for-lunar-water-deepens) of the Moon’s water will provide a firm basis for any comparative analysis on the origins of Earth and Luna.

## Chang’e and Chandrayaan contribute

Modern missions have contributed to the endeavor of figuring out the specifics of our Moon and Earth’s origin story.

With robotic instruments for surface-only studies becoming increasingly advanced, [scientists suggested in 2021](https://doi.org/10.3847/PSJ/abee7f) that even non-sample-return missions can now provide some significant insights with higher precision measurements in key and diverse places on the Moon. India’s [Chandrayaan 3](https://jatan.space/chandrayaan-3-makes-historic-touchdown/) mission falls in that category. It landed on the Moon’s nearside in August 2023 at the near-polar location of [69.37°S, 32.32°E](https://jatan.space/chandrayaan-3-makes-historic-touchdown/#the-moment-of-touchdown), far away from Apollo and Luna sampling sites. The Chandrayaan 3 rover [Pragyan](https://jatan.space/chandrayaan-3/#a-lunar-region-never-explored) made lunar soil composition measurements using its X-ray spectrometer, finding it broadly similar to Apollo samples. This bolstered our Moon’s fully molten origin scenario as laid out by the GIH, or at least [extended its validity](https://jatan.space/moon-monday-issue-190/) to high-latitude regions on the nearside. There’s also a small chance the rover [might have stumbled upon lunar mantle material](https://jatan.space/moon-monday-issue-224/) amid measurements of volatiles. Its detection of such materials makes the [Chandrayaan 3 landing region](https://jatan.space/chandrayaan-3-makes-historic-touchdown/#the-moment-of-touchdown) a potential [mantle sampling location](https://jatan.space/moon-monday-issue-39/) for future missions and studies of the Moon and Earth’s origins. From [the paper](https://doi.org/10.1038/s43247-025-02305-1):

> Prior to ISRO’s Chandrayaan-3 mission, there were no in-situ volatile abundance measurements from the lunar southern high-latitude highlands. Consequently, our understanding of the variations in the concentrations of volatiles across the lunar surface is constrained by the limited scope of measurements obtained primarily from lunar samples collected from equatorial regions. This points to a substantial gap in our understanding of the mechanisms governing enrichment-depletion of volatiles such as sodium (Na), potassium (K) and sulfur (S) on the Moon.

![](https://jatan.space/content/images/2026/05/ch3-rover-apxs-measurements-of-lunar-crust.jpg)

****Top left:** The Chandrayaan 3 rover rolling out of the lander’s ramp during pre-launch testing; ****Bottom left:** The co-added spectrum from all 23 lunar surface soil and rock measurements by the rover’s X-ray spectrometer; ****Right:** An artist’s concept of our Moon shortly after its formation, with a magma ocean and a newly forming rocky crust. Images: [ISRO](https://www.isro.gov.in/Chandrayaan3%5Fcurtainraiser%5Fvideo.html) / [Santosh Vadawale, et al.](https://www.nature.com/articles/s41586-024-07870-7.epdf?sharing%5Ftoken=4ZQFD5zK9GT9acs31FeVNNRgN0jAjWel9jnR3ZoTv0MR1M6jsWV0QR20SmA7k7Hvrkyl3GgMk99HFFb15nD09447WpwTLcpEaBgvj9C4YhThW7GJgQ7WgMAckZYS0fZ6FTf8RdEwv0eX%5FN4HvzLxBwhFq2fqKCzi0YsrWI%5FcfAQ%3D) / [NASA Goddard](https://www.dlr.de/content/en/articles/news/2020/03/20200710%5Fa-slightly-younger-moon.html)

Of course, more grounded and more versatile studies still require and benefit from samples. In 2024, China’s[Chang’e 6](https://jatan.space/moon-monday-issue-174/) spacecraft [collected samples](https://jatan.space/moon-monday-issue-179/) from the Moon’s farside, a world first. Since then, fervent studies of the samples have [transformed our understanding of the Moon’s evolution](https://jatan.space/moon-monday-issue-233/) by anchoring key events in the lunar timeline. In one such study, Chinese researchers analyzing two grams of Chang’e 6 samples found the [isotopic measurements of key chemical elements](https://doi.org/10.1126/science.adt3332) to be compatible with a fully molten young Moon. Chang’e 6 thus lent unequivocal credence to the GIH, anchoring a key event in the Moon’s origin and evolution.

Another Chang’e 6 study analyzing 578 particles revealed for the first time that the Moon’s farside mantle [contains less water](https://doi.org/10.1038/s41586-025-08870-x) than within the nearside, another factor in the [contrasting farside-nearside volcanic activity](https://jatan.space/the-two-faced-moon/). The finding added to [the debate on the topic](https://jatan.space/moon-monday-issue-85/) in a grounded and unique way, favoring the GIH hypothesis that our Moon indeed lost most of its water and its constituents amid a fiery formation.

![](https://jatan.space/content/images/2025/07/chang-e-6-lander-on-the-moon.jpg)

A panorama from China’s Chang’e 6 lander on the Moon’s farside, showing one of its legs and the scoop sampling arm near its surface digs. Chang’e 6 collected 1.93 kilograms of soil and rocks across scoops and drills. [Image: CNSA / CLEP](https://x.com/SegerYu/status/1798688466026594539)

## Future findings

While [various](https://web.archive.org/web/20121103215146/http://www.nasa.gov/topics/solarsystem/features/moon%5Fformation.html) [forms](https://doi.org/10.48550/arXiv.1410.3819) of [modifications](https://www.skyandtelescope.com/astronomy-news/could-a-giant-impact-have-vaporized-earth-to-create-the-moon/) of the GIH have been proposed to account for deviances in evidences, the fact remains that specifics of the Moon’s and Earth’s origin stories are still a mystery. Despite the fact that Apollo missions [landed in largely similar geological areas](https://jatan.space/apollo-landing-sites-overview/), they still transformed our understanding of the Moon’s possible origins. At the same time, its results left us with more knowledge but farther away from a firm conclusion, a common outcome in complex scientific research. Chandrayaan and Chang’e results added nuanced layers to our understanding gained from Apollo while opening new questions still.

To continue piecing together the complex origin and history of the Earth-Moon system, we need samples from new locations, including geologically pristine rocks below the lunar surface, the poles, and the farside. We need to probe the nature of [water on the Moon’s poles](https://jatan.space/ultimate-guide-to-water-on-the-moon/) and [in the lunar interior](https://jatan.space/moon-monday-issue-177/#the-search-for-lunar-water-deepens) to know their origins. A nice, detailed review paper, [*Origin of the Moon*](https://doi.org/10.48550/arXiv.2103.02045), summarizes recent advances in our knowledge. The paper highlights ten key datasets that would clear the dust on our Moon’s formation. This includes getting a better understanding of the role of magnetic fields, which [likely accelerated the process](https://doi.org/10.3847/2041-8213/abbffd). An unintuitive inclusion in the list is measuring the isotopic composition of [Venus](https://jatan.space/why-explore-venus/) so that we can get a better hold on what made the inner solar nebula, and thus Theia and early Earth. Upcoming missions to Venus [from India](https://jatan.space/indian-space-issue-20/), [Europe](https://jatan.space/esa-envision-mission-to-venus/), and [the US](https://jatan.space/nasa-veritas-mission-to-venus/) could provide anchor points to that end.

![](https://jatan.space/content/images/2024/02/https-3a-2f-2fbucketeer-e05bbc84-baa3-437e-9518-adb32be77984-s3-amazonaws-com-2fpublic-2fimages-2f80676e27-0f16-4cec-8705-df7edd4b8178_1475x1600-jpeg.jpg)

****Top panel:** Shocks propagating through the bodies during the collision of Earth and a Mars-sized planet (0–0.5 hours). ****Middle panel:** The tidal arm of debris (2–14 hours). ****Bottom panel:** The proto-lunar disk (24–48 hours). See [animation](https://iopscience.iop.org/article/10.3847/2041-8213/abbffd#apjlabbffdf1). [Image: P. D. Mullen, and C. F. Gammie](http://www.astroexplorer.org/details/apjlabbffdf1)

Later this decade or early next, India’s [Chandrayaan 4](https://jatan.space/moon-monday-issue-241/) & [Chandrayaan 5](https://jatan.space/indian-space-issue-25/) spacecraft as well as several crewed missions [from China](https://jatan.space/moon-monday-issue-267/) and the US’ [Artemis program](https://www.nasa.gov/humans-in-space/artemis/) aim to explore south polar sites, which are [intertwined scientifically](https://doi.org/10.1038/s41586-025-09582-y) to the Moon’s internal structure and thus its formation and evolution. The poles are also where [water ice](https://jatan.space/ultimate-guide-to-water-on-the-moon/) and other volatiles persist, allowing us to close in on the truth. Other than findings from on-ground measurements, there will be studies of samples from Chandrayaan 4 and crewed missions, which are expected to contain pieces of ancient crustal and potential mantle materials. Much like Apollo, studying a fresh set of novel samples will likely transform not just how we look at our Moon and Earth but also the Solar System and beyond. Luna’s pristine interior compared to other geologically active worlds means it helps researchers understand the baseline layer of processes that drive the interior evolution of rocky worlds everywhere.

![](https://jatan.space/content/images/2024/02/https-3a-2f-2fbucketeer-e05bbc84-baa3-437e-9518-adb32be77984-s3-amazonaws-com-2fpublic-2fimages-2f8c672e4e-1970-467b-8dca-b352ed273996_1344x756-jpeg.jpg)

Illustration of astronauts doing science on the Moon and collecting samples. [Image: NASA](https://www.nasa.gov/press-release/nasa-names-companies-to-develop-human-landers-for-artemis-moon-missions)

What a profound success it would be to identify the origin story of our dear Moon and Earth. Being the [most accessible and well preserved body](https://jatan.space/why-explore-the-moon/) in our Solar System to study fundamental planetary processes, our Moon beckons. 🌙

---

*Originally published in 2018, significantly updated and rewritten in August 2026 to include new research findings and reflect the new mission landscape.*

*Thanks to* [*Phil Stooke*](http://publish.uwo.ca/~pjstooke/) *from University of Western Ontario for having fact-checked the original version of this article. The original article was republished by* [*The Planetary Society*](http://www.planetary.org/blogs/guest-blogs/2018/apollo-moon-origin.html)*, and featured as part of its* [*special coverage for the 50th Apollo anniversary*](http://www.planetary.org/explore/space-topics/space-missions/apollo-50-years.html).