Comets are basically packs of ice, made of water
and gas, and dust orbiting stars at high speeds. What is strange
about these celestial objects is that they did not form any planets
during the early parts of their lives while the solar system was
forming. This queer aspect makes them an interesting specimen to
study if one is interested in the early universe.
The comets in our solar system, such as Comet Halley, usually have
very long orbits and spend most of this time away from the sun.
During these periods, comets appear to be just simple heaps of rock,
dust and ice traveling through the cosmos. But when a comet is traveling
towards and near the sun, it has several clear parts: the nucleus,
coma, hydrogen cloud, dust tail and ion tail. The nucleus is a mostly
solid, stable core composed of ice, gas, dust and some other solids.
The coma is the part of the comet in which the water, carbon dioxide
and other gases have sublimed, or turned from a solid phase directly
to a gaseous phase. The Hydrogen cloud is a giant envelope of hydrogen
gas surrounding the comet. The dust tail is the very prominent feature
of the comet that can be seen with the unaided eye. This tail can
often be millions of kilometers long and is made up of small sized
dust particles driven off the nucleus by the escaping gas. The ion
tail is even longer than the dust tail, often as much as 100 million
kilometers in length. This tail is made of plasma and other effects
created by the comet's interaction with the solar wind.
As said before, many comets in our solar system
often have huge orbits; some even exceed the orbit of Pluto. But
as they make their return trip to the sun, they begin to encounter
more and more solar wind. But what is solar wind? The sun does not
only emit vast amounts of heat and energy, it emits large amounts
of protons and electrons: charged particles. These particles, when
emitted in large quantities and at high speeds have the power to
affect many things. This solar wind is known to cause beautiful
events such as Aurora Borealis but also causes unwanted effects
like power surges.
Due to their size and speed, comets have the power to severely damage
anything in their path. The chances of any comet impacting the planets
in our solar system are greatly increased because the comet's orbit
often intersects the orbits of other planets, and many close encounters
have been recorded. Comets are amazing objects and continue to fascinate
many people today.