surrounding it. what exactly is a coma in this context and where does the green come from? >> a comet is basically a giant mountain of mush, a frozen mush, and as it comes in towards the sun, it heats up, and as it heats up, the ices begin to melt and vaporize. so the coma is a gas and plasma that surrounding the comet that recently went from the ice age to the gaseous state. the green comes from actually light from the sun ripping apart molecules like cyanide or carbon's, adams that are glued together, so it's that green hue telling you that the surface of the comet is kind of being torn apart by the intense light from the sun. >> again, if you missed it this time, it may not exist in a few more years, because it may get torn apart, so don't get upset. professor, great to talk to you, thank you very much, really helping us understand this marvel that we have seen. >> it was a real pleasure, thank you. >> the news continues, cnn tonight with laura coats is next, right after a short break.