This picture of Eros, the first of an asteroid taken from an orbiting spacecraft, is a mosaic of four images obtained by NASA's NEAR mission immediately after the spacecraft's insertion into orbit.

Asteroids are rocky, airless worlds that orbit our sun, but are too small to be called planets. Tens of thousands of these "minor planets" are gathered in the main asteroid belt, a vast doughnut-shaped ring between the orbits of Mars and Jupiter. Asteroids that pass close to Earth are called Near-Earth Objects (NEOs).

Featured Mission: Dawn
NASA's Dawn mission is on a 3-billion-km (1.7-billion-mile) journey to the asteroid belt to orbit asteroid Vesta and dwarf planet Ceres. Scientists hope to characterize the conditions of the solar system's earliest days by studying these two very different worlds.

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