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Asteroids
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Asteroids:
Black and white image of asteroid Eros.
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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Just the Facts
Discovered in 1801, Ceres was the first asteroid discovered. It has since been reclassified as a dwarf planet because it is more like a planet that its neighbors in the main asteroid belt.

About once a year, an automobile-sized asteroid hits Earth's atmosphere, creates an impressive fireball, and burns up before reaching the surface.

Asteroids that populate the main asteroid belt between Mars and Jupiter, and pose no threat to Earth, can be as big as 940 km (about 583 miles) across.
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YSS Theme: Failed Planets Seeking Revenge
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Edward Weiler Edward Weiler
Dr. Edward J. Weiler was named Associate Administrator of the Science Mission Directorate at NASA Headquarters in Washington, D.C. in May 2008. Read More...
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Last Updated: 11 Jan 2011