National Astronomical Observatory of Japan

Giant Impact of Protoplanets


In the final process where a planet like the Earth is born, Mars-sized objects called “protoplanets” collide with each other and grow into a larger rocky planet like the Earth. These impacts among protoplanets are called “giant impacts.” It is thought that our Earth and Venus experienced these impacts multiple times. Also, there is a theory that our Earth’s moon was born from these great impacts. In this video we visualized the collision of two protoplanets that are about the same size as Mars.

The Dynamic Birth of a Planet

The collision speed was assumed to be about 5 kilometers per second in this simulation. This speed is about ten times faster than that of pistol bullet. Most rocks melt to mush because the impact speeds are very fast and the temperatures of the colliding areas become hotter than 5,000 Kelvin due to the impact energy. In addition, some parts evaporate to gas, and they surround the post-collision planet.

This simulation is the case where the protoplanets collide obliquely, as opposed to a head-on collision. This makes the coalesced protoplanet rotate at a high speed. Therefore, a large amount of melted rock is scattered at the equatorial plane by rotational movement, and a disk is formed. The disk formed in this way cools down subsequently and a large-sized satellite such as our Moon may form.

Virtual Reality (VR) Video

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Translations by: Hiroko Tsuzuki and Ramsey Lundock (Public Relations Center, NAOJ)

Video Data

Computer Usedgeneral-use computer ELSI VT-Cluster
Time Scaleabout one day
Spatial Scaleprotoplanets about 5,000 kilometers in diameter
Calculations byHidenori Genda (Earth-Life Science Institute at Tokyo Institute of Technology)
CreditsHidenori Genda, Hirotaka Nakayama, Four-Dimensional Digital Universe Project, NAOJ

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