Planet Lab: build a world, then break it
Pick a star, set an orbit, add air, oceans, moons and life. This interactive planet simulator computes orbital timing, stellar energy, global temperature, ice feedback, surface gravity and a broad habitability indicator from your settings. Regional weather, impacts and other explanatory layers are clearly labeled when they are illustrated rather than calculated. Three modes cover everyone: Play for quick experiments, Explore for students and the curious, Expert for scientists who want the equations.
How to read the orbit simulation
In Orbit view, the green rings are the star's estimated habitable zone. The brighter middle band is the conservative range; the paler edges show a wider optimistic range. Green does not mean a planet is inhabited, or even automatically habitable. It only marks distances where a rocky world could receive suitable starlight for liquid surface water if its atmosphere and climate also cooperate.
The dashed curve is the planet's Kepler orbit, with the star at one focus. Eccentric planets move faster when they pass close to the star and slower when farther away. Orbit distances use a logarithmic display so very close and very distant worlds fit in one view, while star and planet sizes are enlarged for inspection. Hover, tap, or keyboard-focus the visual key to identify each layer.
What makes this simulator different
Most planet builders let you paint a temperature onto a globe. Here temperature is an OUTPUT: sunlight in, reflection out, greenhouse trapping the difference, and the ice-albedo feedback looping on top. Freeze the planet and it gets brighter, reflecting more light and freezing harder; warm it and the darkening surface accelerates the melt. Those loops preserve the real direction of the climate feedback in a deliberately simplified global model, and you can feel them in the sliders. Expert mode shows every equation used, so the simplifications are inspectable rather than hidden.
What-if scenarios
- 🥶 Snowball EarthReduce sunlight and greenhouse warming, then compute the ice-albedo feedback.
- 🔥 Runaway greenhouseSwap in a Venus-class atmosphere and inspect the new hot, dry equilibrium.
- 🛑 Stop the spinSlow Earth's rotation almost to a stop, then compare the period with teaching overlays.
- 🌑 Steal the MoonRemove Earth's visible Moon; tides and long-term tilt changes remain context.
- 🙃 Tip it on its sideSet Earth's axial tilt to 90 degrees and watch the illumination geometry change.
- ☀️ Age the SunReplace the Sun with a simplified red giant and move the habitable zone outward.
- 💪 Super-EarthIncrease Earth's radius and density, then compare mass, gravity, and escape speed.
- 👁️ Eyeball worldPlace a slow-rotating world close to a red dwarf and inspect its fixed heating pattern.
- 💍 Give Earth ringsAdd a stylized ring system and inspect its approximate changing shadow on Earth.
- ☄️ Asteroid impactStage an inbound object, contact flash, shock ring, and crater at Chicxulub.
- 🌊 Mega-tsunamiLaunch schematic expanding wavefronts on an Earth baseline.
- 🫠 Melt the iceRaise greenhouse warming, remove modeled ice, and separately increase ocean coverage.
- 🌀 Spin it fastSet a five-hour rotation period and add a schematic high-wind appearance.
Common questions
Is the physics real?
It is real and honestly simplified. The temperature comes from a zero-dimensional energy balance (the same first model climate students learn), years from Kepler's third law, the habitable zone from published stellar flux bounds, and gravity from radius and density. There is no weather model or carbon cycle; Expert mode lists every equation and every shortcut.
What does the habitability score mean?
It is a broad scenario indicator, not a prediction: a summary of temperature, water, atmosphere, gravity and stellar environment with the top reasons listed. Real habitability depends on chemistry and history no slider can capture.
Can I share the planet I built?
Yes. The page URL updates as you build, so copying it shares your exact world. The Card button also downloads a picture of your planet with its vital statistics.