Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune — the eight major planets — form the classic architecture of the Solar System. The inner four are small, rocky, and dense; the outer four are gas and ice giants that together contain 99% of the system's orbital angular momentum. Jupiter's mass dominates the planetary zone, shepherding asteroids and shielding the inner planets from cometary bombardment. Saturn's rings and Uranus's tilted axis add further diversity. No moons, asteroids, or dwarf planets are included — just the eight worlds on their Keplerian paths. Initial positions and velocities are from JPL Horizons for 1 January 2025.