Planet Simulation is a Dan-Ball game which simulates planets' universal gravitation released on April 2006. On 29th May, 2015 the game received HTML5 support, the third title to do so after Font Game and Liquid Webtoy.

Planet Simulation

This shows Planet Simulation in action.


Left-clicking on the screen performs the action specified by the current Tool. Right-click has no effect. The status bar displays the following information:

  • S, M, L - Count of Small, Medium, and Large objects currently in the simulation.
  • SUM - Total object count, including Stars.


In addition to the tools listed, the tool area has four blank spots which can be selected, but have no effect.


Changes the colour of objects released. Select "?" for random colors. On the iPhone version of the game, the color yellow with a large planet has rings around it like Saturn. This does not occur on the online version.


Changes track left from an object. Options are Line (the default), Long Line, Point (a series of dots), and Non (None).


Places an object in the simulation with a specified direction and speed. Click the starting point, and drag to set trajectory. Red line indicates initial velocity and points in direction of travel. Release to start the object moving. Of course, the actual path will depend on the gravitational force of other objects in the simulation.


Places random objects into the simulation. The number (1-5) indicates the velocity of the objects released. Hold down mouse to continuously release objects.


Places an object in the simulation with a direction and speed that will put it in a circular orbit around the nearest Star. Note that the orbit will be disturbed by the gravitational force of other objects. This option is not available in the iPhone version.


Changes size of objects placed in simulation. Sizes are S(mall), M(edium), and L(arge). These objects interact gravitationally, and can also collide with each other.

When two objects collide, the results depend on their relative size.

If one object is larger, then the smaller object simply disappears. Note that mass is lost in this case; objects do not accrete mass. The large object's trajectory is also changed slightly, if the smaller object is made up of many small objects put in the same place the change in trajectory would be very large.

If the objects are both Large, then both objects shatter, and six Small objects are generated from each Large object. Their velocity and direction are roughly equivalent to those of the parent objects, with a little bit of random scatter.

If the objects are both Medium, then both objects shatter. One of the colliding bodies generates two Small objects, and the other generates three Small objects.

If the objects are both Small, then the objects pass each other; they do not collide. This allows multiple small masses to be put in the same place, acting like a denser object of the same size.

Assuming the number of objects created in a collision is related to the relative mass, then the mass of objects is as follows:

  • 2 Medium = 5 Small; 1 Medium = 2.5 Small
  • 1 Large = 6 Small = 2.4 Medium
  • Sun = unknown

The gravity of 6 Small masses put in the same place is less then that of a Medium and 15 Small masses has a smaller gravity then a Large mass. This shows that most of the mass is lost in a collision.


Creates another star, which is a high gravity point similar to the black hole in Earth Editor. Stars do not move relative to the viewer, or to each other. Anything that falls into a star is absorbed (again, its mass is lost). To remove a star, select the star tool and click an existing star.


Scales in and out from the screen. A scale of 1 corresponds to approximately 2 AU (Astronomical Units, compared to the default yellow star and blue object).


Toggles speed of action. In addition to 0 (all stop) and 8 (very fast), this simulation includes 1/2 and 1/4 speed.


Resets game field to one Large blue object around one yellow star.

Effects in Planet Simulation

Some examples for effects which can be created with Planet Simulation are:

  • Create a small moon in orbit around a large planet, while it orbits a sun.
  • Create a binary star system and send a planet into an eight-shaped loop around it.
  • Observe various details of details of orbital mechanics, for instance, orbital precession.


Version Date Thumbnail New features and changes Blog[1]
2.0 15/06/2018 PS ver2.0 Bug fix (Scrolling while playing the game on smartphones). jp/en
1.9 15/07/2016 PS ver1.9 Optimization (60 FPS, Font). jp/en
1.8 29/05/2015 PS ver1.8 HTML5 Support. jp/en
1.7 04/02/2007 Tool addition (Speed). jp/en
1.6 26/11/2006 Tool addition (Circle). jp/en
1.5 30/07/2006 Game dimensions increased. jp/en
1.4 10/07/2006 Star addition. jp/en
1.3 09/05/2006 Scale changes. Objects are deleted if they leave the border. jp/en
1.2 03/05/2006 Random added to colour selection. Planet collision mechanism added. jp/en
1.1 25/04/2006 Tool addition (Track and Random). jp/en
1.0 20/04/2006 Game creation. jp/en
  1. The original blog is written in Japanese. A link to an automatic translation into English by Google is also available.

External links

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