National Astronomical Observatory of Japan



From Planetesimals to Planets (Formation of Terrestrial Planets)


This video visualizes a computer simulation of how Earth-like rocky planets are born. Not so long before the Sun is born, a protoplanetary disk is born. The disk is formed from dust particles and gasses leftover from the formation of the Sun. The dust condenses under gravity and becomes planetesimals about several kilometers in diameter. Protoplanets are built up through the collisions of planetesimals over millions of years. The protoplanets orbit stably around the Sun for a while, but eventually they collide with each other. In about 100 million years, several terrestrial planets, like the ones found in our Solar System, are formed.

The Earth’s History is a History of Collisions

In the first half of the movie, we show how objects collide. Dust grains build up to form planetesimals, and planetesimals merge to form protoplanets. Watch the protoplanet shown in red, it collides and merges with another protoplanet. These types of collisions between protoplanets are called “giant impacts.” Some researchers believe that the Moon, the Earth’s satellite, was formed from a giant impact. (See 4D2U Contents “Formation of the Moon”.)

In the latter half of the video, we describe the evolution of the protoplanets’ orbits. We can see that the protoplanets’ orbits are often severely disturbed by the gravity of other protoplanets. Giant impacts occur at the intersection points of the protoplanets’ orbits. Finally, we see four terrestrial planets being formed in this simulation.

Video Data

Computer UsedGRAPE-6
Number of Particles Used in Calculations10,000-30,000
Time Scale1,000,000 years
Spatial Scale1 AU
ResearchersPlanet Formation:Eiichiro Kokubo (NAOJ), Giant Impacts: Hidenori Genda, (Earth-Life Science Institute, Tokyo Institute of Technology)
CreditSimulation: Eiichiro Kokubo and Hidenori Genda, Visualization: Hitoshi Muller, Four-Dimensional Digital Universe Project, NAOJ

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