9.12: Comets
Often called dirty snowballs, comets are really more like snowy dirtballs. Presently, there are around 5,000 known comets; with new comets being discovered all of the time. The number of known comets is much smaller in number than the known number of asteroids. Many comets orbit in the Kuiper Belt and the Oort Cloud . Comet orbits are often highly elliptical, so much so that these orbits are sometimes described as cigar-shaped. Comet orbits around the sun can be a short period (<200 years) or a long period (>200 years).
Comets are named after their discoverers, which is a tradition that spans centuries. And hundreds of years ago some European astronomers made their living discovering comets.
We have seen a comet impact a planet; Comet Shoemaker-Levy 9 impacted Jupiter with 21 cometary fragments in July 1994. Gene and Carolyn Shoemaker and David Levy discovered the comet.
“Comets are like cats. They both have a tail and they both have a mind of their own…”
—David Levy (1994)