Good question; as with any comet the answer is as elusive as ever. Predictions go from a total bust with the comet disintegrating as it rounds the Sun to possibly being bright enough to easily see. The latest observations are now leaning toward a visible comet.
Astronomers have recently determined ISON is rotating with its axis pointed toward the Sun. Only half of the comet is being “heated” which may explain why the comet is not hitting its brightness predictions. The hope is, and I mean hope, as the orientation of the comet’s axis changes much more of the comet will be exposed to the Sun. In other words the still frozen side of the comet, which has significant volatile materials, could spew forth copious amounts of stuff as the comet passes inside the orbit of Mercury. With the comet so close to the Sun this material will outgas rapidly creating huge tail.
In any event Comet ISON will go down in the history books as the first comet to be observed and photographed from another planet. The Mars Reconnaissance Orbiter (MRO) got pictures of the comet. Granted the photos are not spectacular (pretty lousy actually) casting further doubt about the comet’s brightness and chance of surviving passage around the Sun on November 28, Thanksgiving. In the MRO’s defense; it was never designed to photograph comets and after all it is a pretty amazing first.
As it stands right now it’s about 50/50 we will see a bright comet in early December. I am just hoping ISON does not turn out to be a turkey. One thing Comet ISON will not be is its original prediction as the best comet in 400 years. Too bad!
Wishing you clear skies