Comet ISON will fly by Mars on Tuesday (Oct. 1), then gear up for a close solar approach that will bring the icy wanderer within 724,000 miles (1.16 million kilometers) of the sun's surface on Nov. 28. If ISON manages to stay in one piece, it could put on a memorable sky show around that time, experts say.
Here's the lowdown on Comet ISON and its journey through the inner solar system, which scientists are already observing with a phalanx of instruments on the ground and in space. [Photos of Comet ISON: A Potentially Great Comet]
FIRST STOP: Comet of the Century? Maybe Not...
A spectacular show is certainly possible, experts say. But Comet ISON probably won't live up to the most breathless hype.
"More likely, ISON will be one of the brightest comets in the past several years and, thanks to the global astronomy community, we hope one of the most broadly observed comets in history!" researchers with the NASA-organized Comet ISON Observation Campaign (CIOC) wrote in a recent status update.
NEXT: Comet ISON Isn't Huge
So ISON appears to be an average-size comet, or perhaps a bit smaller than average. It's certainly a far cry from giant icy wanderers like the 19-mile-wide (30 km) Comet Hale-Bopp, which lit up Earth's night skies during its pass by the sun in 1997. [Amazing Comet Photos of 2013 by Stargazers]
NEXT: An Inner Solar System Newbie
This explains some of the uncertainty in the forecasts of ISON's performance. It's difficult to predict how any comet will behave during a close solar passage, experts say, and especially tough to do so for "dynamically new" comets like ISON.
NEXT: Many Eyes Watch Comet ISON
Most sungrazers pop onto scientists' radar for the first time just hours before their solar encounters, but ISON will let them track a comet's evolution over a much longer period of time. Further, ISON is the first dynamically new sungrazer in at least 200 years, CIOC team members say.
To take advantage of this opportunity, CIOC is coordinating a global observation campaign that employs a variety of assets both on and off Earth. For example, NASA's iconic Hubble Space Telescope has joined the effort, as have sun-watching spacecraft such as NASA's Solar Dynamics Observatory and the agency's twin Stereo probes, as well as the Solar and Heliophysics Observatory, which is operated jointly by NASA and the European Space Agency (ESA).
More farflung spacecraft spacecraft are participating as well, such as NASA's Messenger probe around Mercury and a variety of Mars spacecraft (more on that below).
NEXT:Comet ISON Buzzed Mars
ISON missed the Red Planet by just 6.5 million miles (10.4 million km) on Oct. 1. ESA's Mars Express Orbiter has already begun observing the comet, and NASA's Mars Reconnaissance Orbiter was expected to start doing so soon after.
NASA's 1-ton Curiosity rover, which has been exploring the Martian surface since August 2012, may even see Comet ISON zoom overhead during the flyby, researchers said.
NEXT:Comet ISON found by Amateurs
Russian amateur astronomers Vitali Nevski and Artyom Novichonok spotted the comet on Sept. 21, 2012, using photographs taken by a telescope run by the International Scientific Optical Network (whose acronym explains how the comet got its name).
NEXT: Comet ISON Won't Doom Earth
ISON will miss Earth by 40 million miles (64 million km) during its swing through the inner solar system. And so will its bits and pieces, if the sun's gravity happens to tear the comet apart along the way.
"During a breakup, comet fragments don't fly off in different directions like shards in a cinematic explosion," explains a new Comet ISON video released by the operators of the Hubble Space Telescope. "They break off but continue to travel along the path of their parent body. So any pieces would remain far from us, millions of kilometers away."
NEXT: You May See Comet ISON Soon
Provided ISON survives its solar close shave — and there's certainly no guarantee that it will — the comet may then be visible to the naked eye sometime in early December, in the western sky just after sunset. Observers in the Northern Hemisphere will have a much better view of ISON than folks in the South, CIOC officials say.