The surface of Comet 67P/Churyumov-Gerasimenko, as seen by the ESA Rosetta mission.
Image: ESA/Rosetta/MPS for OSIRIS Team/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA.

Comets are icy denizens of the solar system. They are leftover stuff from the formation of our solar system. As these Icy objects approach the Sun, they begin to sublimate. This process creates a gaseous atmosphere called a coma and contributes to the formation of tails.