They are rich in many different elements.
I guess they want to get a foot hold where the real money will be made
edit on 20-2-2011 by pazcat because: (no reason given)
NASA Weighs Asteroids: Cheaper Than Moon, But Still Not Easy 1. Richard A. Kerr Summary Rather than first returning astronauts to the moon before heading off to Mars, NASA will be aiming for near-Earth asteroids (NEAs) as steppingstones in the human exploration of deep space.
