Solar System

Our Solar System is part of a spiral galaxy known as Milky Way. The Sun, the center of our Solar System, holds eight planets and countless smaller objects in its orbit. The age of the Solar System is 4 billion and 568 million years. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets. Jupiter and Saturn, are gas giants and the two outermost planets, Uranus and Neptune, are ice giants.

The asteroid belt of the Solar System is a circumstellar disc orbiting between Mars and Jupiter. It is thought to be remnants from the formation of Solar System that failed to come together because of the gravitational interference of Jupiter. The asteroid belt consists of hundred of thousands objects over one kilometre in diameter. However, the total mass of the asteroid belt is a thousandth of that of Earth and is sparsely populated. Ceres is the largest object in the asteroid belt with a diameter of approximately 945 kilometers (587 miles). Composed of rock and ice, it mass is about one third of that of the entire asteroid belt.

The Kuiper belt is a Solar System circumstellar disc beyond the planets, extending from the orbit of Neptune. It is similar to the asteroid belt, but it is far larger and consists mainly of small bodies, or remnants from the Solar System's formation. Most Kuiper belt objects are composed largely of frozen volatiles such as methane, ammonia and water. The comets with orbital period of less than 200 years originate in the Kuiper belt.

The Oort cloud is a theoretical cloud of predominantly icy small bodies believed to surround the Sun at a distance of 1.5 to 2 light-years. Long-period comets (orbital period more than 200 years) are directed towards the Sun from the Oort cloud by gravitational deviation caused by passing stars and other galactic phenomena. The comets, having a hyperbolic orbit may pass once through the inner Solar System before being thrown out to interstellar space.

Solar System

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