How it works

Every body attracts every other body with Newton's law F = G·m₁·m₂ / r². Positions and velocities are advanced with a symplectic leapfrog (kick-drift-kick) integrator in AU, days and solar masses, so energy stays conserved over long runs. Nothing is scripted: planets and moons only follow gravity from their starting conditions (real masses, distances, eccentricities, inclinations).

Things to try

• Select Jupiter and raise its mass ×50 — watch the inner planets and the Sun wobble.
• Launch a probe with Launch mode; drag faster than the escape speed (shown in the tooltip) and it leaves the Solar System.
• Drop a Rogue star and see orbits get stretched, captured or flung away.
• Turn on Reverse time — gravity is time-reversible.
• Change G and see why orbital speeds and periods depend on it.

Display scales

Planets and the Sun are drawn far larger than real, and moon orbits are spread out (slider) so they remain visible. This only affects rendering — the physics uses true distances. Collisions are detected at physical radii and merge bodies, conserving momentum.

Shortcuts

Space pause · +/− speed · L launch mode · T trails · N labels · F follow selected · Esc deselect · ? this help