protoplanetary disk

A protoplanetary disk is a swirling cloud of gas and dust surrounding a young star, from which planets form. These disks are crucial in the process of star formation. Within the disk, eddies of material, known as protoplanets, condense and grow through accretion.

The composition and size of the forming planets depend on their distance from the central star. Closer to the star, higher temperatures prevent volatile substances like water from condensing into ice, resulting in smaller, rocky inner planets. Further out, beyond the "snow line," where temperatures are low enough for ice to form, planets can accumulate more mass, including abundant hydrogen and helium, leading to the formation of massive outer planets. Observations of other solar systems have revealed planets orbiting very close to their stars, challenging some aspects of these formation models.1