So, if we can see the nucleus of a comet, what is going on?
Comet nuclei are mostly made of what we call volatile compounds, which is to say, things that can melt or evaporate (How they formed and why they continue to survive in the solar system will be addressed later). The most abundant volatile in a comet is water, which is why they are often referred to as ‘Dirty Snowballs’. As a comet nears the Sun, the volatile compounds begin to melt off in increasingly larger amounts. This evaporation can occur generally over the surface of its nucleus or from active sectors that produce jets (Hyakutake Jets picture). A typical active comet can lose 5000 gallons of water, enough to fill a small backyard pool, every second (Inner tube picture). Along with that water are all manner of other nasty sounding compounds, things like carbon monoxide, ammonia, cyanide, alcohol and other hydrocarbons, and soot. Indeed, the environment near a comet bears a more than passing resemblance to the exhaust pipe of a car that’s burning oil. As unappetizing as this recipe
