OF THE
TIMES
Cometary nuclei are composed of an amalgamation of rock, dust, water ice, and frozen gases such as carbon dioxide, carbon monoxide, methane, and ammonia.Dangerous Close Cometary Encounters occur when:
As such, they are popularly described as "dirty snowballs" after Fred Whipple's model.
However, some comets may have a higher dust content, leading them to be called "icy dirtballs".
https://en.wikipedia.org/wiki/Comet
Comment: A few days ago an unidentified fireball was filmed over the city of Krasnodar in southern Russia.