The solar system

Planet Earth is part of a vast space neighborhood called the solar system. Our solar system is an amazing place. Our solar system is one of many groups of planets that are part of the Milky way galaxy. About 15-20 billion years ago, there was an enormous explosion called the Big Bang. Whirling clouds of dust and gas filled the Universe. Over time, gravity made some clouds start to group together. Big groups formed galaxies. Smaller groups became stars. Then, about 4.5 billion years ago, the clouds that formed our solar system spun so fast they formed a disk. The center of the disk became so hot it dropped out. That center became the sun. The dust and gas that didn’t get sucked into the center stuck together in groups. These groups became planets. Our solar system was born. The eight planets of our solar system revolve around a large star called the sun. The sun is the center because it’s HUGE. More than one million Earths could fit inside it. It contains more than 99.8% of all the mass in the solar system. Its size gives it the gravity it needs to hold the solar system together. The sun’s gravity pulls the objects down while they keep trying to move away. It’s a never-ending tug-of-war that keeps the planets in their orbits instead of flying off into space. Pluto was once the ninth planet in our solar system. But in 2006, scientists kicked it out of the lineup. Why? They had come up with new rules about what makes a “real” planet. Pluto just didn’t measure up. Pluto is shaped kind of like a potato. It has a weird orbit that sometimes crosses into Neptune’s. And it has a lot of debris orbiting around it.

Vocabulary