Give a world a little push.

Newtonian gravity in two dimensions, with every body attracting every other body. Kick–drift–kick leapfrog integration uses small adaptive steps for close encounters. The Sun is free to move. Physical contact merges bodies, conserving mass and linear momentum; this simplified collision loses kinetic energy.

Solar-system presets use circular, coplanar orbits with representative masses and distances. They are not a prediction of today’s planetary positions. Drawn body sizes are enlarged for visibility; collision radii use physical sizes. Very close encounters can slow simulated time. Relativity, tides and atmospheric drag are excluded.

Data: NASA planetary fact sheets ↗. AU = 149,597,870.7 km. Reduced motion starts the experiment paused.