What is the biggest asteroid?

Ceres is the biggest asteroid with a diameter of approximately 590 miles. It was discovered by Giuseppe Piazzi in 1801, though he considered it a planet. Ceres is spherical in shape and orbits the sun between Mars and Jupiter in the Asteroid Belt.

Ceres was the first asteroid ever discovered and is sometimes referred to as a dwarf planet. It is distinguished by a rocky core and an icy surface. In January 2014 scientists discovered vapor emissions from Ceres using data from the Herschel Space Observatory. As of 2014 no visit has been made to Ceres, but the spacecraft Dawn is scheduled to explore the asteroid by early 2015.