In October, 1991, the first close-up views of the asteroid Gaspra were taken by the Galileo spacecraft on its way to Jupiter. Gaspra is an irregularly shaped body 19 by 12 by 11 kilometers (12 by 7.5 by 7 miles) whose rocky surface is covered with impact craters.
The minor color differences in this enhanced image show subtle variations due to surface texture and possibly composition.
Ida and Dactyl
The Galileo spacecraft also encountered the asteroid Ida. Close inspection of the image data revealed a small object - believed to be a satellite orbiting Ida. Ida's moon was named Dactyl. Ida is roughly 58 by 23 kilometers (36 by 14 miles) and Dactyl is about 1.2 by 1.4 by 1.6 kilometers (.74 by .87 by .99 miles).
Phobos and Deimos
Mars has two known moons, Phobos and Deimos, that may be asteroids that were captured by the planet's gravitational field.
In 2005 the Japanese spacecraft Hayabusa imaged the rugged terrain of Itokawa, a small asteroid 550 meters (about 1800 feet) across. After experiencing some difficulties, Hayabusa was able to land on the asteroid, collect a small sample, and return it to Earth in 2010.
In July 2011, NASA's Dawn spacecraft went into orbit around Vesta, the second most massive object in the Asteroid Belt.