The Solar System's Formation

The Solar System’s Formation

The solar system began about 4.6 billion years ago in a cloud of stellar dust within a larger cloud called a nebula. The cloud collapsed, possibly after a shockwave from a nearby exploding star compressed it, and the material formed a disk.

At the center, pressure grew high enough for hydrogen atoms to fuse into helium, releasing energy and forming the Sun. The Sun gathered more than 99% of the disk’s material.

Planets and dwarf planets formed from the remaining material as gravity drew particles together and collisions built larger bodies. Some grew large enough to become spherical.

Different materials formed planets in different regions:

• Rocky planets formed close to the Sun, where heat prevented icy and gaseous material from surviving.
• Farther away, gas and ice collected to form the giant planets.

Some material never became part of a planet. Asteroids in the asteroid belt are leftover fragments, while distant comets are icy objects that have changed little since the solar system formed. Asteroids and comets help scientists study the solar system’s history and reconstruct how it formed.

Speakers and Sources

• Narrator: Unidentified voice presenting the explanation.
• Source: NASA Space Place.