This is the NEAR spacecraft.
Right now, everything we know about asteroids comes from telescopic observations and four accidental fly-bys of asteroids. So we know a fair amount about the color and albedo of asteroids, and this allows us to make inferences about the composition of the asteroid, but we have no way of knowing how accurate our guesses are.
The NEAR mission is going to gather conclusive data on the mineralogy and chemical composition of Eros. It has six instruments with which to do this.