But he will never forget it. Comets, no matter how numerous, remain one of the enigmas of the galaxy. In 1993, a Dutch scientist named Jan Oort identified what he thought was a cloud of such debris, which was named the Oort belt. He estimated that there might be 100 billion such independently operating comets, ranging in size from several yards to a few miles across. Every year they keep coming in.
Comets come from various families.
One object called Chiron was first believed to be a planet or a giant asteroid, locked into orbit around Jupiter. Now astronomers reckon it may be a comet. One crashed into Jupiter several years ago. Occasionally one of the sun-grazing family of planets will crash into the sun. One, named after the Sol-Wind satellite that discovered it, was never seen by human observers because of the sun's glare.