Today an interloper from the farthest reaches of our solar system is zooming past the sun at over 350,000 miles per hour. This migrant left its home in the Oort Cloud roughly a million years ago and was detected by our telescopes only a little over 14 months ago. Comet ISON, it's formally called, after the name of the Russian-based International Scientific Optical Network that discovered it. More formally, it is known as C/2012 S1: "C" for comet, "S" for September, and "1" for being the first comet found that month.
Comets are in essence dirty snowballs made up of rocks, dust and ice. Not just any ice, though: carbon dioxide ice, ammonia ice and methane ice, along with good old water ice. These are frozen in various concentrations around bits of dust and rock. When comets enter the inner solar system, often as they pass Jupiter or Mars, the ices begin to vaporize -- giving the comets their characteristic fuzzy appearance. The closer they get to the sun, the more the ices vaporize, and the more bits of dust and rock are released in a stream of particles left in the comet's wake. There's a lot more to it than that, but you get the idea.
Astronomers have been watching Comet ISON with great excitement, because comets that originate in the Oort Clour are like the fossils of the solar system. By studying them, we can better learn the distribution of elements when the sun and the planets first formed. This in turn allows us to improve our understanding of planet formation and enhances our ability to hypothesize about the alien worlds we are discovering more and more of every day around other stars in our galaxy.
At this very second, Comet ISON is passing within 800,000 miles of the sun's surface. That's 1/100th of the distance between the earth and the sun. What remains to be seen is what's left of the comet after such a close encounter with a giant ball of fusion. There is a possibility that both the radiation and gravitational force of the sun will rip ISON's nucleus apart, leaving nothing but a trail of dust and gas. But if ISON remains intact, it will round the sun and head in our direction for a Christmas flyby. Provided it's still basically in one piece, there should be some great viewing opportunities from the northern hemisphere.
If you can't wait until then, or if you've got comet fever like me, NASA will provide real-time updates on the comet this afternoon starting around 1 P.M. EST. I'm pretty sure that slots in nicely between football games, right?