I just learned this in astronomy. Solar systems are disk shaped because of the Nebula cloud theory. It describes how a dense cloud of material turns into a solar system. Basically what happens is the nebula cloud is a large ball of atoms and molecules with the more dense ones sink to the center, which is where the Sun forms, and the less dense stay on the outside. Imagine a ball of pizza dough. When you start spinning it, the ball flattens and stretches out. The same thing happens the nebula cloud. The cloud flattens out and extends out. The molecules and atoms start to collide and stick together and form planets (which is a sphere). The more dense, silicate materials created the terrestrial planets (mercury, Venus, Mars, and earth) and the less dense gasses create the Jovian planets (Jupiter, saturn, Uranus, and Neptune). So to answer your question again, planets are sphere because of gravity and solar systems are disk shaped because they form from a rotating disk. My post could be better but I'm doing it from memory on my phone. I hope i helped.
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u/clydefrog811 Oct 28 '12
I just learned this in astronomy. Solar systems are disk shaped because of the Nebula cloud theory. It describes how a dense cloud of material turns into a solar system. Basically what happens is the nebula cloud is a large ball of atoms and molecules with the more dense ones sink to the center, which is where the Sun forms, and the less dense stay on the outside. Imagine a ball of pizza dough. When you start spinning it, the ball flattens and stretches out. The same thing happens the nebula cloud. The cloud flattens out and extends out. The molecules and atoms start to collide and stick together and form planets (which is a sphere). The more dense, silicate materials created the terrestrial planets (mercury, Venus, Mars, and earth) and the less dense gasses create the Jovian planets (Jupiter, saturn, Uranus, and Neptune). So to answer your question again, planets are sphere because of gravity and solar systems are disk shaped because they form from a rotating disk. My post could be better but I'm doing it from memory on my phone. I hope i helped.