Comets; puny objects in the black sky that pales in comparison to the stellar bodies we prevalently know as planets. They are, in essence, a clump of ice, frozen gases that didn't get used in the creation of the solar system, and dust. Hence the nickname, "dirty snowball". Since it contains material that dates back to the start of the universe, it makes it a very valued object to study.

    A comet has 3 main parts. The first being the nucleus. This part is not generally shown because it is usually concealed by the bright coma that always encompasses it. The coma is the part of the comet we usually see. It is actually a mixture dense clouds of water, carbon dioxide and other neutral gases. The third part is the hallmark of the comet: the tail. There are fact 2 tails. The first and most prominent, is the dust tail. This tail is formed by blown off smoke-sized dust particles and could sometime reach as long as 10 million km long (6200000 mi). The second tail is the ion tail. This tail is made of gases and is more easily affected by solar wind.

     Comets are usually fairly small; they are most prevalently found like that. In addition, they just harmlessly orbit around the sun burning off its ice until one day it runs out. In the case its does go through earth's atmosphere, it will become what we commonly know as a "shooting star". The light that we see is, again, the tail and is visible by the naked eye because of the extreme abrasion that the comet experience when it enters the atmosphere. Due to its main composition being dry ice, the comet tends to lose most of its mass when if goes through the atmosphere and ends up being a harmless speck of rock. So commonly, it has no adverse effect on human life. Moreover, the chance for one to hit us could be tomorrow to one that hits us a million years from now.  One particularly devastating comet was the one theorized to have hit earth and caused the extinction of the dinosaurs.

Artist rendering of comet hitting Earth

    Comets are usually defined in 2 ways: long-term ones and short-term ones. Long term comets are those that take more than 200 years to revolve once around the sun or may be a tangent and never come back again. Usually, these comets come from the Oort cloud. This expansive cloud of maybe over 3 trillion comets encompasses our solar system 18 trillions miles away from the sun and is believed to be the remains during the creation of the solar system. Short-term comets – comets that have a revolution around the sun in less than 200 years – are believed to have come from the Kuiper Belt. This belt, located beyond the orbit of Neptune, is also believed to be remnants during the creation of the universe and acts as a reservoir for short term comets. One such comet is the Halley's Comet
 

Top: Artist rendering of Oort Cloud

     This was a mission launched by NASA as an attempt to study the materials of a comet more closely. The Stardust Spacecraft was set to coincide with Comet Wild 2 and use aerogel - a new "wonder" item that's designed to absorb space and comet dust - to capture particles from the comet that might yield answers to evolution of the universe and origin of life and send it back to earth. The mission was successfully completed on Jan 15, 2006 at Utah Test and Training Range at 2:10am (Pacific).

Top: Artist rendering of Stardust Craft

Bottom: Hand holding a piece of aerogel