Wavelength is another word for color. Reflectivity is another name for brightness. The asteroids named on this diagram did not crash into Earth, but are asteroids that are still orbiting in the Asteroid Belt between Mars and Jupiter. This book treats the topic in more detailed and is a good book for someone who is technically oriented, though not necessarily a scientist. Pieces break off or the orbit may be changed.
Asteroids can only stay in certain orbits.
Once their course is deflected, the gravity of the planet Jupiter can fling asteroids or fragments out of the Asteroid Belt and into an orbit that crosses the orbit of the Earth. That Ended The Mesozoic Era . This is a well-done educational piece, but you need a Macintosh to see the full pictures. More about Asteroids. The Web has some excellent resources on asteroids.