Comets

Comets are known as “dirty snowballs,” because they consist of a mixture of ices (both of water and frozen gases), carbon dioxide, ammonia, methane, and dust. The core of a comet is solid and it consists of ice and dust.

Comets also have two tails. The first tail is an ion tail. The ion tail is blue because it consists of ionized CO+ and it scatters blue light. The second tail is the dust tail. The dust tail is green and consists of the dust that is pushed off of the comet and reflects radiation from other sources. The tails of a comet can reach 160 million kilometer long. 

 

The average comet has a mass of 10^14 kg, a diameter of 20 km, a density of 0.6 g/cm^3, and an albedo of .05.

Comets are mostly located in the Oort cloud, except for the occasional comets that streaks through the inner solar system. The Oort cloud holds millions and millions of comets and the Oort cloud is found much farther out than the orbit of Pluto. It is generally believed that we got our water when comets collided with the Earth.