What evidence supports the theory of planetary accretion?

Evidence supporting the theory of planetary accretion includes the presence of planetesimals, meteorites, and the uniform direction of planetary rotation.

The theory of planetary accretion suggests that planets form through the gradual accumulation of smaller bodies, known as planetesimals. These planetesimals collide and stick together, gradually growing larger over time. One of the key pieces of evidence supporting this theory is the existence of these planetesimals themselves. Astronomers have observed numerous small bodies within our solar system, such as asteroids and comets, which are believed to be leftover planetesimals from the formation of the solar system.

Meteorites also provide evidence for the theory of planetary accretion. These are pieces of rock that have fallen to Earth from space, and their composition can tell us a lot about the early solar system. Many meteorites are found to contain tiny, spherical grains known as chondrules. These are thought to have formed in the early solar system, and their presence in meteorites suggests that these rocks are remnants of the planetesimals that came together to form the planets.

Another piece of evidence comes from the rotation of the planets. Most of the planets in our solar system rotate in the same direction as they orbit the Sun, which is consistent with the theory of planetary accretion. This uniform direction of rotation suggests that the planets formed from a rotating disc of gas and dust, with the planetesimals gradually coming together and maintaining the overall direction of rotation.

In addition, the distribution of different types of planets in our solar system also supports the theory of planetary accretion. The inner planets, including Earth, are rocky and small, while the outer planets are gas giants. This is consistent with the idea that planetesimals close to the Sun were made of rock and metal, which could withstand the Sun's heat, while those further away were made of ices, which could survive in the colder outer regions of the solar system.