Step through the giant-impact hypothesis for how the Moon formed - drag the stage slider from "before impact" to "present-day orbit".
Published teaching figures: Theia was roughly Mars-sized (about 10% of Earth's mass in the canonical model); impact about 4.5 billion years ago at roughly 45 degrees; today's Moon is about 384,400 km away and 3,474 km across.
Drag to orbit and scroll or pinch to zoom. Click Earth, Theia, or the Moon for facts, or move the stage slider through the five stages of the impact.
Moon Formation Giant Impact 3D Explorer
freetoolonline.com editorial team
This browser explorer steps through the giant-impact hypothesis: a Mars-sized protoplanet called Theia collides with proto-Earth, throws a debris disk into orbit, and that disk accretes into the Moon. Drag the stage slider to jump between five moments, or click Earth, Theia, or the Moon for their facts.
In the canonical model, Theia was roughly Mars-sized and held about 10% of Earth's mass, though some alternative models push that as high as 30-45%. The two bodies collided about 4.5 billion years ago, during the early Hadean eon, at an oblique angle of roughly 45 degrees and a speed above 9.3 km/s at the moment of contact. Oxygen-isotope ratios in Apollo Moon rocks show heavy mixing between Theia and Earth material, which is part of why the impact is modeled as a glancing blow rather than a head-on hit.
How fast the Moon actually assembled from the debris disk is still debated: classic models describe accretion over decades to about a century, while a set of 2022 simulations proposed that part of the Moon's core could have formed within hours to days by direct ejection into orbit, skipping the slow disk-accretion step entirely. This page does not pick a single number for that step - it shows the disagreement as published.
- Five staged views: before impact, impact, debris disk, Moon accretion, present-day orbit
- Click Earth, Theia, or the Moon in the scene for a facts panel with the published figures
- Stage slider (0-4) jumps directly to any moment in the sequence
- Drag to orbit the camera, scroll or pinch to zoom
- Runs fully in the browser with the vendored three.js engine - no account, no upload
Students see why the Moon's makeup resembles Earth's mantle more than a random asteroid; teachers use the stage slider to separate "what is settled science" (an impact happened, a Moon-forming disk followed) from "what is still debated" (Theia's exact mass, the accretion timescale); curious readers get a feel for how close in size the two colliding bodies really were.
| Quantity | Value |
|---|---|
| Theia size | roughly Mars-sized (~10% of Earth's mass, canonical model) |
| Estimated impact time | ~4.5 billion years ago (early Hadean eon) |
| Impact angle / speed | ~45 degrees, over 9.3 km/s at contact |
| Moon diameter | ~3,474 km (~27% of Earth's diameter) |
| Mean Earth-Moon distance today | ~384,400 km |
This page teaches how the Moon itself came to exist. For what the Moon does once it is already there, the collection also has phase, calendar, libration, barycenter, and tidal pages: Moon Phases and Moon Calendar 3D cover its monthly light cycle, Moon Libration explains why we see slightly more than half its surface over time, Earth-Moon Barycenter shows the wobble the Moon's gravity causes in Earth's own orbit, and Tides Earth-Moon covers the ocean-tide effect - each of those is about the Moon's behavior today, while this page is about its origin billions of years ago.
Everything renders on your device with WebGL. The 3D engine loads once (about 0.7 MB) and is cached; no scene data is sent to a server.
This is an educational approximation of the giant-impact hypothesis, not a physics simulation - real impact modeling uses N-body gravity codes and smoothed-particle hydrodynamics that this scene does not run.
Frequently Asked Questions
What does the Moon Formation Giant Impact 3D Explorer show?
Five staged views of the giant-impact hypothesis: proto-Earth and Theia before impact, the impact itself, the debris disk it throws into orbit, the disk accreting into the Moon, and the Moon's present-day orbit.
How big was Theia compared to Earth?
Roughly Mars-sized. The canonical model puts its mass at about 10% of Earth's, though some alternative models suggest as much as 30-45%.
When did the giant impact happen?
About 4.5 billion years ago, during the early Hadean eon, at an oblique angle of roughly 45 degrees and a speed above 9.3 km/s at the moment of contact.
How long did it take the Moon to form after the impact?
This is still debated. Classic models describe the debris disk accreting over decades to about a century; a set of 2022 simulations proposed that part of the Moon's core could have formed within hours to days by direct ejection into orbit. The scene shows both figures rather than picking one.
Is there any evidence of Theia left inside Earth today?
Possibly. Two continent-sized, dense regions deep in Earth's mantle - called LLSVPs - have been hypothesized by 2023 impact simulations to be leftover Theia material, though this is an active research question, not settled fact.
Is this a physics simulation?
No. It is an educational approximation of the giant-impact hypothesis, not an N-body or smoothed-particle-hydrodynamics impact solver. The published figures shown in the facts panel come from the cited research literature.