When you see a model showing our solar system, all of the planets, and even asteroids, orbit at roughly the same plane. With all the space around the Sun, one might wonder why this is the case.
The explanation for this phenomenon can be found by going back in time to the very formation of the solar system, that is, 4.5 billion years ago. As Nader Haghighipour, an astronomer at the University of Hawaii at Manoa, explains, the solar system at that time was just a massive cloud of spinning dust and gas. This cloud had a diameter of about 12,000 astronomical units (AU), one AU corresponding to the distance between the Earth and the Sun, or roughly 150 million kilometers.
According to the researcher, the cloud kept growing and eventually collapsed on itself and contracted due to its own mass. At the same time, the cloud of dust and gas flattened like a pizza dough being tossed and whirled in the air.
The formation of the Sun
Unlike pizza dough, in the middle of the swirling cloud, the gas molecules clumped together until their temperature rose significantly. With the high temperature and pressure, the hydrogen atoms began to coalesce to form helium, and this activated the nuclear reaction that will last for billions of years. It is about the formation of the Sun.
Over the next 50 million years, the Sun continued to grow, collecting gas and dust from its surroundings, and ejecting intense heat waves and radiation. Gradually, an empty space began to form around him.
Around the planets and asteroids
Haghighipour explains that as the Sun grew, the cloud continued to collapse and form a disc around the star. This disc became increasingly flat and continued to expand with the Sun at its center. At some point it became what is called a protoplanetary disk.
For tens of millions of years, the dust particles in this protoplanetary disc swirled gently, and sometimes collided with each other. Some got stuck, and after a while the particles became grains, then the grains became pebbles of the order of a centimeter.
At some point, all of the material on the disc clumped together to form massive objects. Some of these objects grew so large that gravity eventually shaped them into spheres, forming planets, dwarf planets, and moons. Other objects took a more irregular shape and we were able to obtain asteroids, comets, or even certain small satellites.
The point is that all these objects formed from the protoplanetary disk have remained on one plane all this time. This is why we now have this configuration.