Questions about asteroids, bodies in the solar system smaller then planets which orbit the sun.
Asteroids are defined as
"any of numerous small celestial bodies composed of rock and metal that move around the sun (mainly between the orbits of Mars and Jupiter)."
The first asteroid, Ceres, was discovered between the orbits of Mars and Jupiter in 1801. At the time it was considered to be a planet, but as astronomers discovered more similar bodies in the same region of space, the term "asteroid" was created by Sir William Herschel in the mid-nineteenth century to differentiate them from planets (Ceres has since been reclassified again as a Dwarf Planet). The region between Mars and Jupiter, known as The Asteroid Belt, potentially contains millions of asteroids, but most of them are less than 1 km in diameter.
Other asteroids exist in co-orbital points around planets, especially Jupiter. These asteroids are referred to as Trojan Asteroids. There are also asteroids with different orbits, some that even cross the paths of planets, including Earth.
In June 2010, JAXA returned the first collected sample of an asteroid from space with its Hayabusa mission.
Questions related to past, current, and future missions to asteroids, and the related science, should use this tag.