Astronomers around the world are breathlessly watching a comet - a relic from when our solar system was formed - head toward the sun, where it might break up in a stunning light show.
Comet ISON has been on a journey that may have taken millions of years to get from the edge of the solar system to where it's closing in on our sun. And by studying ISON, scientists hope to gain clues to the ancient formation of the solar system and its planets.
"The reason we study comet ISON to begin with is it's a relic," Carey Lisse, a senior research scientist withJohns Hopkins Applied Physics Laboratory, said during a NASA news conference today. "It's a dinosaur bone of solar system formation. You need comets in order to build the planets. This comet has been in a deep freeze half way to the next star for the last four and a half billion years. It's just been coming in over the last few millions years and possibly even started around the dawn of man."
The comet, which is smaller than normal at about three-quarters of a mile across, is expected to come within a million miles of the sun's surface.
Since ISON is a loosely packed formation of ice and dust, there's an approximately 70% chance it won't survive traveling so close to the sun's blazing hot surface. The comet is expected to get relatively close to the sun on Thursday, which could offer spectacular images for NASA's telescopes and spacecraft to capture.
"It's going from a deep freeze to the furnace of the sun and we're going to watch it bake and boil," said Lisse. "We want to actually see the light coming from that evaporation.... It's like experiments you did in high school, in which you could see blue green for copper or red for iron. We're going to do the same thing for our comet dust."
Jim Green, director of NASA's planetary science division, said ISON is likely on its first orbital trip close to the sun.
"It's a special comet," he added. "It's probably the first time it's come in from a very long distance away - right at the edge of what our sun's gravity can hang on to. It may have taken millions of years to get to this location."
Green noted that ISON has quickly become the most observed comet in history.
Along with the Hubble Space Telescope, five others also have been used to track and study the comet. Even the Mars Reconnaissance Orbiter has turned its imagers on ISON as it flew past.
Karl Battams, an astrophysicist with the Naval Research Laboratory, noted that this is a critical time for ISON.
"When it's closest to the sun, it's experiencing the most intense solar radiation and gravitational forces," he explained. "There are a lot of things that could happen to this comet. Will it fall apart? Will it not fall apart? Will it fade away? We need to see what it does and when it does it and why it behaved the way it did."
NASA's scientists said some believe that the comet already is breaking apart, casting out large chunks of itself. But Lisse thinks that while some pieces may have been cast off, the comet is still holding together.
If it does break up, pieces will be scattered toward the sun where they'll flare and burn up.
"If it's just burping and bubbling and stays a coherent body, it will be heated and stressed by solar gravity," said Lisse. "Some think it could survive and be fine and come back out again."
Sharon Gaudin covers the Internet and Web 2.0, emerging technologies, and desktop and laptop chips for Computerworld. Follow Sharon on Twitter at @sgaudin, on Google+ or subscribe to Sharon's RSS feed . Her email address is email@example.com.