... But after its orbit was better determined it was clear that it was not a comet but more like a small planet. ... M ore than 7000 asteroids have been discovered. ... There are 26 known asteroids larger than 200 km in diameter. ... But we know very few of the smaller ones; perhaps as many as a million 1 km sized asteroids may exist. ... T he largest asteroid by far is 1 Ceres . ... The NEAR spacecraft will orbit the near-Earth asteroid 433 Eros giving our first in-depth information about an asteroid.....