Close encounter with a surprise visitor from deep space
To ancient stargazers, comets (from the Greek for hairy star) were signs of heavenly displeasure. Actually, they are stray bits of debris, largely ice and dust, left over from the formation of the sun and its family of planets nearly 5 billion years ago. Skywatchers around the world got a rare chance last week to view such a dirty celestial snowball close up, at least by astronomical standards. The surprise visitor from deep space swept to within 2.9 million miles of earth, the nearest approach by a comet in two centuries.
Like all comets,...