Physics – 6.1.2 The Solar System | e-Consult

The accretion model suggests the Solar System originated from a collapsing solar nebula – a vast cloud of gas and dust. Gravity initiated the collapse, causing the nebula to spin faster and flatten into a rotating accretion disc. The distribution of materials within the nebula was not uniform; it varied with distance from the protosun.

The interstellar cloud contained a range of elements. The inner regions, closer to the protosun, were hot enough for only materials with high melting points (metals and silicates) to condense. This resulted in the formation of rocky planets like Mercury, Venus, Earth, and Mars. Further out, where temperatures were lower, volatile substances like water, ammonia, and methane could also freeze. This allowed icy particles to accumulate, leading to the formation of the gas and ice giants (Jupiter, Saturn, Uranus, and Neptune). The presence of these icy materials significantly increased the mass of these planets.

The accretion disc was essential. Within the disc, particles collided and stuck together through electrostatic forces and gravity, gradually growing into planetesimals. These planetesimals then continued to accrete material, eventually forming protoplanets and ultimately the planets we see today. The rotation of the disc also played a role in the planets’ orbital plane being roughly the same. The gravitational interactions between the growing planetesimals and protoplanets also influenced their orbits and final positions.