Comets are pieces of ice and rock left over from the
formation of stars and planets. In our solar system, they usually
drift through space in the Oort Cloud, an area beyond our solar
system filled with debris.
A comet has two main parts to it: a head and a tail.
As a comet approaches the inner solar system, the Sun begins
to vaporize the ice and rock. The result of this vaporization
is a tail of ionized gas that appears as a streak behind the
comet. There is also plasma and an envelope of hydrogen separate
from the tail, but they are not visible on Earth. Only spacecraft
have been able to detect these formations.
The most famous and scientifically interesting incident
with a comet was the collision of Shoemaker-Levy 9 with Jupiter
in 1994. In an earlier pass close to Jupiter, the comet was broken
up into several pieces. When it came around again, it was set
to collide with Jupiter. During the course of a week, the fragments
struck Jupiter near its southern pole on the far side from Earth.
The collisions disturbed the gas giant, causing gas bubbles and
scarring in the surface that looked like scorch marks. From this
unique opportunity, astronomers were able to see firsthand the
effects of a comet's impact and may able to explain how such
an impact would affect Earth.
Comets do not come around as often as they should. You
should make the most of every opportunity to go outside and see
a comet for yourself. They are a sight to behold!
For more information on comets, consult the following
- Windows to the Universe has a good description of comets as well as
an interactive comet animation.
- Solarviews has a small
site on the Shoemaker-Levy 9 impact with Jupiter,
including several photos of Jupiter with impact marks.
- NASA'S Jet Propulsion Laboratory has comet observations,
including details on upcoming comet sightings.