Formation of the Moon

How were the Earth and Moon formed? Watch this movie visualizing the results of a computer simulation and learn about the giant impact hypothesis.

At the end of the formation of the Earth, it grew through repeated “giant impacts”, collisions with other protoplanets. The Moon is thought to have been formed by the last giant impact.
A protoplanet about the size of Mars crashes into the Earth. If the body had made a head-on collision, it might have merged with the Earth. Instead, it collides with the Earth at an angle, blasting debris into orbit around the Earth, forming a disk. The Moon then forms from this disk.
As the materials cool into a lava-like state, they collect into numerous small moons through their own gravity. These small moons merge and grow quickly.
The Earth’s tidal force prevents materials close to it from clumping together. The clumps can be seen growing at the appropriate distance.
After about 1 month, all of the small moons have gathered together into one big clump, which is the Moon. This is the most accepted theory for the formation of the Earth and Moon.

640x480, WMV format ( zip file : 30.1 MB)

320x240, MPEG-1 format ( zip file : 10.8 MB)

Details of numerical simulation

"Giant impact"
Based ModelGiant impact hypothesis
PurposeProtolunar disk formation by giant impact
ModelComputational technique: N-body + SPH (polytrope)
Particles: 6×104 particles
Time scale Several days
Spatial scale4-5 Earth-radii
ResearcherRobin M. Canup(Southwest Research Institute)
ReferenceR. M. Canup, W. R. and E. Asphaug 2001, Nature, 412, 708-712
"Moon Accretion"
Based ModelGiant impact hypothesis
PurposeThe accretion of lunar materials in a protplunar disk
ModelComputational technique: N-body (GRAPE) + Rubble Pile
Particles: 1×105 particles
Time scale One month
Spatialscale4-5 Earth-radii
ResearcherTakaaki Takeda (NAOJ)
ReferenceTakeda & Ida, 2001, ApJ, 560, 514-533


  • Simulation: Robin M. Canup, Takaaki Takeda
  • Visualization: Takaaki Takeda
  • Four-Dimensional Digital Universe Project, National Astronomical Observatory of Japan

Release date

  • 2015.9 version1.0 released on the 4D2U English website.
  • 2009.10 version1.0 released on the 4D2U Japanese website.