The only asteroid in the main belt visible to the naked eye is Vesta, which has a mean diameter of 530km and contains nine per cent of the entire asteroid belt’s mass.
The way comets and asteroids are distinguished relies on visual appearance, with comets displaying a perceptible coma behind them while asteroids have none.
Once an asteroid has been discovered it can only be named under the consultation of the International Astronomical Union, who will approve or disapprove the proposition.
The first true asteroids to be photographed close up were Gaspra in 1991 and Ida in 1993. They were imaged by the Galileo space probe en route to Jupiter.
The latest asteroid to be landed on is Itokawa, an S-type asteroid that crosses the path of Mars. The Hayabusa space probe returned to Earth with a surface sample.