For more than three decades, as the frozen mass hurtled along its lonely path, the distant star had grown bigger and brighter in the blackness of space. Now the icy wayfarer was picking up speed, and the star had become a shining yellow sphere, its intense light illuminating the planets circling it. Basking in the rays of the star, the approaching comet warmed, giving off vapors that formed a growing cloud around it. And in the brightening light, the cloud began to glow.
For inhabitants of earth, the third closest planet to the star, the long- awaited spectacle had begun. After...