The Formation of Our Solar System

The Sun's Origin in a Stellar Nursery and the Formative Solar System

Our Sun is believed to have been born within a crowded stellar nursery, a region where numerous stars emerge from a single, dense molecular cloud. This early cluster environment likely had a profound impact on the developing solar system. Clues to this influence are found in the mass distribution of the solar system's outer regions and the peculiar orbits of distant objects like Sedna. The detection of short-lived isotopes, such as iron-60 and aluminium-26, in primitive solar system materials indicates that the early solar system was exposed to the energetic events of nearby massive stars, possibly within the same star-forming region. The Sun's formative years may have been characterized by dynamic interactions with other stars, the intense radiation from nearby stellar giants, and the effects of supernova explosions, all of which played a role in shaping the solar system's architecture.

The Assembly of Planets from the Protoplanetary Disk

The planets of our solar system formed from the protoplanetary disk, a rotating disk of gas and dust that surrounded the young Sun. Through a process known as accretion, dust particles collided and adhered to one another, gradually building up to form larger bodies. These aggregates became planetesimals, the precursors to planets, which continued to grow through further collisions and accretion over time. The inner solar system, with its higher temperatures, favored the formation of rocky planets from refractory materials like metals and silicates. These materials were less abundant, which limited the size of the terrestrial planets. Conversely, the cooler outer solar system, beyond the frost line, allowed for the accumulation of volatile ices, leading to the formation of the gas giants. These larger planets were able to attract substantial atmospheres of hydrogen and helium due to their greater mass.