Disks · accretion · other worlds
From a swirling disk of gas and dust to thousands of confirmed planets around other stars — explore exoplanet formation hands-on, with simulators, games and challenges. Hover every i for more detail.
From dust to planets
A planet is leftover material from a star's birth. Around the newborn star spins a flat disk of gas and dust; over a few million years, that dust assembles itself — bottom-up — into worlds. Click each stage.
The standard route: dust → pebbles → planetesimals → a solid core. If a core grows big enough (~10 Earth masses) before the gas disperses, it runs away and gulps a giant gas envelope.
An alternative for massive disks: a cold, heavy region collapses directly under its own gravity into a giant planet — fast, and far from the star.
Planets don't stay put. Drag from the disk can spiral a giant inward — which is how "hot Jupiters" end up roasting beside their stars.
The great divide
Close to the star it is too hot for ice; only rock and metal condense, so you build small rocky planets. Past the frost line, water and other volatiles freeze onto grains, suddenly providing far more solid material — enough to grow giant cores quickly. Move the star's brightness and watch the line shift.
How we find them
Most known exoplanets were found by watching a star dim slightly each time a planet crosses in front of it. The depth of that dip reveals the planet's size relative to the star — and its rhythm reveals the orbit.
The fractional drop in brightness δ equals the planet-to-star area ratio. A Jupiter crossing a Sun-like star dims it by ~1%; an Earth, by only ~0.008% — which is why finding small planets needs space telescopes. Drag the sliders and read the dip.
The light curve: brightness vs time as the planet crosses. Deeper dip = bigger planet.
The planet's gravity tugs the star into a tiny wobble, shifting its light blue then red. Reveals the planet's minimum mass — complementary to transits.
Blocking the star's glare to photograph the planet itself. Works best for young, hot, wide-orbit giants that still glow in the infrared.
A planet's gravity briefly magnifies a background star's light. Uniquely sensitive to cold, distant planets — a one-time, unrepeatable blip.
Game · challenge
You are the mission scientist. Each light curve is buried in noise — some hide a real planet transit, some are just a restless star. Call it: planet, or no planet? Crank up the noise for a harder hunt.
Game · challenge
Given a planet's size, mass and orbit, what kind of world is it? Use the clues — small and dense means rocky; big and short-period means a roasted giant.
Could it be habitable?
The "Goldilocks zone" is the band of distances where a planet could hold liquid water — not boiling, not frozen. It depends on the star: dim red dwarfs have it tucked in close, bright stars push it far out. Place a planet and check.
Green band = habitable zone. Drag the planet's distance in or out of it.
Worked examples
Every one of these rewrote what we thought planets could be. Click any for its data and why it matters.
Quick reference
Values are representative and rounded for teaching; habitable-zone and formation models are simplified.