Asteroid is a naturally occurring rocky, metallic, or rocky-metallic object that orbits the Sun and is smaller than a planet. Asteroids are remnants of the early formation of the Solar System approximately 4.6 billion years ago. They formed from the same cloud of gas and dust that produced the Sun and planets, but most never became part of a planet. Because they have preserved much of their original material, asteroids provide important scientific evidence about the conditions that existed during the Solar System's formation.
Most known asteroids are found in the region between the orbits of Mars and Jupiter known as the Asteroid Belt. However, asteroids also exist in other locations, including groups that share a planet's orbit, objects that cross planetary orbits, and populations located beyond the main asteroid belt. Their sizes vary greatly. Some are only a few meters across, while the largest, Ceres, has a diameter of about 940 kilometers (584 miles) and is classified as a dwarf planet rather than a typical asteroid.
Asteroids generally have irregular shapes because their gravity is usually too weak to pull them into a sphere. They do not produce their own light, instead, they are visible because they reflect sunlight. Their compositions vary, with some consisting primarily of rock, others containing large amounts of metal such as iron and nickel, and some containing significant quantities of carbon-rich material and other minerals.
