Dirty Snowballs in Space
the nucleus is the coma which may be over a million km across. The coma
is quite bright, both because of reflected sunlight and because some of
the freed gasses become ionized and radiate.
current theory on the composition of comets came from Fred Whipple in 1950.
It is called the dirty snowball theory. At the center of the comet's head
is the nucleus, typically several kilometers in diameter. This nucleus
is composed of ices of water, ammonia, carbon dioxide and methane with
dust mixed in. The dust particles are smaller than the particles in cigarette
comets have two tails, a gas tail and a dust tail and they may extend 150
million km. Both always point away from the Sun. The dust tail is caused
by dust particles released from the gasses being vaporized. The dust tail
usually curves slightly behind the comet. The gas, or ion tail is composed
of ionized gasses excited by the ultraviolet radiation from the Sun. This
tail is a wispy bluish color and is blown straight back. The gas tail is
brighter than the dust tail.
Copyright © 1997 Kathy
A. Miles and Charles F. Peters II