Mark Weakland 
Lonely Existence of Asteroids and Comets [PDF ebook] 

On a dark night as you watch the sky with your friends, a rock with a fiery tail shoots across the sky. A comet! Asteroids and comets hurtle through space, sometimes a little too close to Earth. But did you know that they are linked to life on this planet? From the asteroid Ceres to Halley’s comet, blast into space and enter the lonely existence of asteroids and comets.