In November of 2013, the universe is throwing a "dirty snowball" right within sight of our Earth. And it could end up being a spectacular sight.
Comet ISON, named after the International Scientific Optical Network, a Russian program that discovered the comet last year. This particular comet is anywhere from 1 to 10 kilometers in size, based on what can be seen of it at this point. It just looks like a tiny speck right now.
But ISON is a "sun-grazer". It will fly through the sun's atmosphere little more than a million km from the stellar surface. And as it nears the sun, it will start shedding ice and particles from its surface, really becoming visible. But a comet that gets this close to the sun could even fly completely apart, the result of which would be a magnificent light show. Even if it survives this trip past the sun, it could emerge glowing as brightly as the Moon, briefly visible near the sun in broad daylight. The comet's dusty tail stretching into the night sky could create a worldwide sensation.
Or the whole thing could fizzle. Some reporters have started calling ISON the "Comet of the Century," but Don Yeomans of NASA Near-Earth Object Program thinks that's premature.
"I'm old enough to remember the last 'Comet of the Century'," he says. In 1973, a distant comet named Kohoutek looked like it would put on a great show, much like ISON. The actual apparition was such a let-down that Johnny Carson made jokes about it on the Tonight Show. “It fizzled,” says Yeomans. “Comets are notoriously unpredictable.”
The trouble with comets is that they are basically "dirty snowballs" flying toward the sun. Tidal forces and solar radiation have been known to destroy comets. A recent example is Comet Elenin, which broke apart and dissipated in 2011 as it approached the sun.
However, another comet that we could compare ISON to is Comet Lovejoy, which flew through the sun's atmosphere in 2011. Lovejoy emerged intact and wowed observers with a garish tail for weeks.
"Comet ISON is probably at least twice as big as Comet Lovejoy and will pass a bit farther from the sun’s surface," notes Matthew Knight of the Lowell Observatory. “This would seem to favor Comet ISON surviving and ultimately putting on a good show."
If ISON does make it through it's whip around the sun on Thanksgiving Day, it could be visible all night in parts of December and January.
Even if ISON breaks up, there is no danger to Earth. The pieces would continue right along the same path the original comet was on.