1. Giant Molecular Cloud: The Sun and all the planets formed from a giant cloud of gas and dust called a nebula. This cloud was mostly hydrogen and helium, with small amounts of heavier elements.
2. Gravitational Collapse: Over millions of years, gravity pulled the particles in the nebula closer together. As the cloud collapsed, it began to spin faster and faster.
3. Protostar Formation: As the cloud collapsed further, the center became incredibly hot and dense. This hot, dense core became a protostar, the precursor to the Sun.
4. Nuclear Fusion Ignition: The temperature and pressure in the protostar's core eventually reached a point where nuclear fusion ignited. This is the process where hydrogen atoms combine to form helium, releasing tremendous amounts of energy. This energy is what powers the Sun and gives it its light and heat.
5. Solar System Formation: The remaining gas and dust around the protostar formed a disk. Within this disk, the planets, moons, asteroids, and comets formed through a process called accretion, where smaller particles gradually clumped together.
So, the Sun didn't "get" into the solar system – it formed the solar system from a giant cloud of gas and dust. The planets, asteroids, and other objects all formed around the Sun as it was developing!
