Protoplanetaire

Protoplanetaire, or protoplanetary disk, is a rotating circumstellar disk of dense gas and dust that surrounds a young star. It forms from the residual material of a collapsing molecular cloud core and the ongoing accretion onto the newborn star. The disk provides the environment in which planets are thought to form, from small dust grains that coagulate into larger bodies.

The disk typically extends from a fraction of an astronomical unit to hundreds of astronomical units and contains a few percent to a tenth of a solar mass, though values vary with the mass of the central star. Temperatures are highest near the star and fall with distance, producing distinct chemical regions; snow lines mark where volatile species condense into ices. The gas component dominates the disk’s dynamics, while dust grains grow from micron-sized particles into pebbles and, ultimately, planetesimals and protoplanets.

Key processes include dust coagulation, gas accretion, and gravitational interactions that can lead to the formation and migration of planets. Observations increasingly reveal substructures such as rings, gaps, and spirals within disks, which are often interpreted as signs of embedded forming planets or dynamic processes within the disk.

Dispersal occurs over a few million years through accretion onto the star, photoevaporation by stellar and external radiation, and disk winds. Protoplanetary disks are distinguished from debris disks by their substantial gas content and active planet formation. They are a central focus in studying the origins of planetary systems and the early evolution of exoplanets.