This interactive protoplanetary disk simulation shows dust and gas orbiting a young star gradually clumping into planetesimals and protoplanets, carving dark gaps in the disk exactly as seen in real ALMA radio-telescope images of young star systems.
In the core accretion model of planet formation, microscopic dust grains collide and stick, gradually building kilometre-sized planetesimals that then sweep up more material through gravity. As a growing body's mass increases, its gravitational reach — modelled here as a growing capture radius — widens, clearing a gap along its orbit that shows up as a dark ring, just as ALMA observations of discs like HL Tauri reveal.
Increase disk density to add more raw material, raise the accretion rate to speed up clumping, and set how many planetary seeds start the process. Simulation speed fast-forwards the orbital and growth timescales so you can watch thousands of simulated years pass in seconds and see gaps open around each growing protoplanet.
The HL Tauri disk, imaged by ALMA in 2014, was the first protoplanetary disk to show clear concentric gaps in a system only about a million years old — direct evidence that planet formation can begin remarkably early in a star's life.
Planets are born in flattened, rotating disks of gas and dust that surround newly formed stars. This simulation models the earliest, dust-dominated stage of that process: microscopic grains orbiting a young star at Keplerian speeds — orbiting faster closer to the star, more slowly farther out — gradually colliding and sticking together into ever-larger bodies called planetesimals, and eventually protoplanets.
As a growing protoplanet's mass increases, its gravitational influence widens, letting it capture dust from an increasingly broad band around its orbit. This process depletes material along that orbital path, carving a dark gap in the disk — a pattern directly observed by the Atacama Large Millimeter Array (ALMA) in real protoplanetary disks such as HL Tauri and TW Hydrae, whose concentric rings are thought to mark forming planets.
Dust particles follow Keplerian orbits (faster at smaller radii); accretion capture radius grows with the cube root of a seed's mass, concentrating growth and clearing gaps.
Disk density sets the dust supply, accretion rate controls how quickly seeds capture material, and the number of seeds determines how many gaps eventually form.
Gaps in real protoplanetary disks are one of the strongest pieces of evidence that planet formation can begin within the first million years of a star's life.
A protoplanetary disk is a rotating disk of gas and dust that surrounds a young star shortly after it forms. It contains the raw material from which planets, moons and asteroids eventually form through a long process of collision and accretion.
In the core accretion model, microscopic dust grains collide and stick together through electrostatic and gentle gravitational forces, slowly building up centimetre, then kilometre-sized planetesimals, which in turn merge and sweep up more material to become protoplanets and eventually full planets.
As a forming planet grows, its gravity clears material from its orbital path, either by scattering it or accreting it directly. This creates a dark, relatively empty gap in the disk at that orbital radius, which shows up clearly in radio and infrared images.
The Atacama Large Millimeter/submillimeter Array (ALMA) is a radio telescope array in Chile capable of imaging cool dust in protoplanetary disks with exceptional resolution. Its images of systems like HL Tauri revealed multiple concentric gaps, offering the clearest visual evidence yet of planets forming in real time.
Dust grains can grow to planetesimal size within tens of thousands of years, while building a full gas giant or rocky planet takes anywhere from roughly one to ten million years, all occurring within the few-million-year lifetime of the gas-rich disk itself.