This Is Why Comets Glow An Eerie Green Color
“But even though things aren’t looking particularly good for this comet, there’s always a chance it will surprise us. Furthermore, the features that you can expect for this comet — the ion tail, the dust tail, the coma, and the nucleus — are common to practically all comets that enter our inner Solar System. When a comet gets warm enough, it creates an extended, gas-rich cloud known as a coma around its nucleus. If the coma contains carbon-nitrogen and carbon-carbon bonds, the Sun’s ultraviolet light will excite the electrons inside it, causing them to emit a green glow when they drop down in energy. And whenever you see that green glow, know that there’s a chance of the comet’s nucleus splitting apart. It may not happen this time, or even most times, but there’s a chance for a visually spectacular show. When it comes to skywatching, it’s hard to ask for more.”
We typically think of comets as frozen mixes of ice and rock, but they’re so much more. There’s dust and volatile compounds present, and when the light and heat from the Sun interacts with the surface, it kicks up molecules into a gaseous, diffuse coma. This coma then gets struck by the ultraviolet light from the Sun. The dust particles get accelerated, creating the main comet tail you’re used to, but there are gas particles in the coma that simply get kicked to higher energies. If there’s enough cyanogen (CN) and diatomic carbon (C2) molecules present, they’ll create a green color due to their atomic transitions. And whenever you see that color, know that there’s the potential for the cometary nucleus to split, creating a spectacular outburst.