According to NASA, gravity is the reason why planets are round. Gravity causes any matter to attract toward any other matter. When planets began to form, the earth���s solar system was one big swirling disk that contained dust and gas, with the sun at its center. Particles of dust and gas pulled toward each other due to gravity.Continue Reading
As these particles of dust and gas clumped together, they continued to attract matter and grow larger until there was no longer any further material to attract. These growing planets swept up any debris like giant vacuum cleaners. Their round shapes were caused by gravity that pulled in an equal direction to the center of these large masses. Any protrusions were pulled back into the center creating the shape of a ball.
Before the invention of the telescope, scientists used careful observations and the naked eye to record the sky. The first visible planets observed were Saturn, Jupiter, Mars, Venus and Mercury. Thousands of years ago, the Greeks discovered objects that displayed different characteristics to the stars. These objects were observed to wander around as visible points of bright light. The word ���planet��� is derived from the word ���planetes," an ancient Greek word that means wanderer.Learn more about Planets