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How the planets formed

The Solar System was born about 4.6 billion years ago, when a great

cloud of gas and dust in space began to collapse. Inside the cloud, particles of gas and dust were pulled together by gravity to form a hot ball, with a disc around it. The hot ball became the Sun, and matter in the disc came together to become the planets. The four planets closest to the Sun— Mercury, Venus. Earth, and Mars—started to form when bits of rocky matter collided with one another and stuck together to form larger and larger lumps. In time the lumps grew in size to become the planets. The gas that was in the inner part of the disc was soon blown away by the force of the rays and particles given off by the new- born Sun. It was blown into the colder, outer reaches of the Solar System, where it became part of the giant outer planets. The four inner planets went on to develop in quite different ways to produce the four quite different bodies we find today.

∆ Earth and its neighbors formed when lumps of matter came together due to gravity.

Close companion Venus is the closest planet to the Earth, but it isn ’ t our closest neighbor in space. That is the Moon , which comes as close to Earth as 224,000 miles (360,000 km). Some of the mini-planets we call the asteroids also sometimes pass within a few million miles of the Earth. A few come even closer. We call them the Earth–grazers.

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