Nebular hypothesis

The nebular hypothesis holds that the Solar System formed when a rotating cloud of gas and dust collapsed under gravity, producing the Sun and orbiting bodies.

Molecular cloud: A cold, dense interstellar cloud of gas and dust where stars can form. The Solar System's proposed starting material was a region within such a cloud.
Immanuel Kant: An eighteenth-century German philosopher who proposed a naturalistic account of Solar System formation. Kant independently developed an early nebular account in 1755.
Interstellar medium: The gas, dust, and other matter occupying the space between stars. The Solar System's precursor cloud was part of this broader material environment.
Protoplanetary disk observation: Astronomical study of gas-and-dust disks around young stars. Observed disks provide direct evidence for a common setting of planet formation.
Streaming instability: A process in which interactions between gas and drifting solids concentrate particles until gravity can bind them. It may explain how pebble-sized solids rapidly formed planetesimals.
Gravitational collapse: The inward contraction of matter under its own gravity. Collapse initiated the transformation of the Solar System's cloud into a compact system.
Pierre-Simon Laplace: A French mathematician and astronomer who proposed that the Solar System condensed from a rotating nebula. Laplace gave the nebular hypothesis a influential mathematical and physical formulation.
Conservation of angular momentum: The principle that total angular momentum remains constant when no external torque acts. It links the cloud's slow initial rotation to the rapidly rotating disk.
ALMA: The Atacama Large Millimeter/submillimeter Array, an astronomical observatory in Chile. Its images reveal rings and gaps in young stellar disks.
Pebble accretion: Planet growth through the capture of small, drifting solid particles called pebbles. Its efficiency may help account for the rapid growth of planetary cores.

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