How Are Planets Formed?

By Amy Lyons


Have you ever wondered how planets come into being? There are many different theories about how planets formed, with the leading theory known as the “protoplanet hypothesis.” This hypothesis states that smaller objects continued to stick together until they grew bigger and bigger. There are many different planets in our Solar System, but let’s begin instead, with the star that gives us life: the Sun.

The Sun was born about 4.6 billion years ago into the Solar System. At the time of the Sun’s creation, the Solar System was only a collection of gas and dust, which is also known as a nebula. Something caused the pressure to change within the center of the nebula’s cloud, perhaps an exploding supernova nearby, and this pressure change led  to the cloud’s collapse, resulting in the creation of a disc material. Within the center of this disc, there was a great increase in pressure that was so powerful, that hydrogen atoms came in contact, fusing together to produce helium, and this resulted in the formation of the Sun. The Sun, at the time, composed 99% of everything that happened to be swirling around, but the 1% that was leftover from the disc, is where planet formation began.

By the time of the formation of the Solar System, it was extremely chaotic with gas, dust, and debris floating about. Nevertheless, planet formation seems to have occurred quickly. The small pieces of dust and gas clumped together and, with the recently-formed Sun pushing out most of the gas to the Solar System, the Sun’s heat evaporated any nearby ice. Eventually, the ice melting resulted in rockier planets closer to the Sun, leaving the gas giants further away.

Then, about 4 billion years ago, an event known as the “late heavy bombardment” occurred, in which the smaller bodies of the Solar System crashed into the larger bodies of the Solar System. Nevertheless, the protoplanets, that is, the planets still forming, survived this bombardment, and now constitute the planets we know today.

There are also still remnants of the formation of the planets to this day. For example, there’s an asteroid belt between Mars and Jupiter that would have clumped together into a planet, but Jupiter’s gravity is too strong.

Of course, this theory as a whole is challenged, because there was no one to take note of the history of the Solar System’s birth.

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