Welcome to Solar System Builder — place celestial bodies into their correct orbits, master Keplerian physics, and earn stars across four timed challenges!

🕹️ Controls & Interaction

• Place Bodies: Click a card in the inventory to select it, then click anywhere near an orbit ring on the canvas to snap it in place.
• Relocate Bodies: Drag any already-placed body on the canvas to a different orbit to reposition it.
• Remove Bodies: Click (without dragging) on any placed body on the canvas to de-orbit and dissolve it.
• Attach Moons: Select the Moon card, then click close to any placed planet on the canvas to attach it as a satellite.
• Slingshot Comets: Select the Comet card, then click-and-drag on the canvas to aim and launch it — watch it slingshot around gravity wells!
• Pause / Resume: Press Spacebar at any time to pause or resume the simulation.
• Recenter Canvas: Click 🎯 Recenter to bring the solar system back to the center of the canvas.

🌌 Simulation Modes

• Orbit Lock: Planets follow stable Keplerian circular tracks — inner orbits move faster than outer ones. Great for ordered placements.
• Chaos Gravity: Removes orbital guides! Bodies become free-floating masses subject to real N-body gravity. Expect collisions, mergers, and rogue trajectories!

🎮 Game Modes

• Experimental: Freeplay with no timer. Drop any body onto the canvas — you'll be warned if you place it in the wrong orbit. The ⓘ icon on each card reveals full specifications and correct orbit info.
• Challenge: Reconstruct the solar system correctly before the timer runs out. The inventory is shuffled and the ⓘ info buttons are hidden — you must rely on your own knowledge!

🏆 Challenge Levels

• Level 1 — Inner Rocky Planets: Place Mercury, Venus, Earth, and Mars in their correct orbits (1–4). ⏱ 60 seconds.
• Level 2 — Gas Giants: Place Jupiter, Saturn, Uranus, and Neptune in orbits 6–9. ⏱ 60 seconds.
• Level 3 — Full Solar System: Place all 8 standard planets in precise orbital order. ⏱ 60 seconds.
• Level 4 — Grand Architecture: Place all 8 planets plus the Asteroid Belt & Ceres (they share the same orbit!) and the Kuiper Belt & Pluto (they also share one orbit!). ⏱ 90 seconds.

⭐ Scoring

• Complete a level correctly to earn 1–3 Stars based on how much time remains.
• Each star awards 15 XP. Your rank is calculated from total XP this session.
• Progression resets on page reload — every session is a fresh start!
• After completing a level, the next level is automatically selected — press Start Challenge when ready.

📚 Encyclopedia (Experimental Mode only)

• Click the ⓘ icon on any inventory card to view its full specifications — classification, mass, relative size, and correct target orbit.
• This panel is hidden in Challenge Mode to keep things fair!

This planet does not belong in that orbit!

Level passed!

Time's up!