Comet ISON (c2012 s1) encountered a solar flare while traveling around the sun and faded quickly. It was thought to have disintegrated, but a short time later it reappeared on one of NASA’s solar observatories. So for a little while there was a faint hope (pun intended) that it had survived. However, as of Dec 3rd, NASA has declared that the comet has broken apart. There is still a dense “debris pile” traveling along the comet’s path and this may still be visible in large telescopes. But this isn’t a comet anymore and won’t have a coma or a tail.
Comet ISON is known as a “sun grazer” – meaning it passes very close to the sun. On Nov 27/28th ISON passed through perihelion (point of closest approach of a body to the sun) with a orbital radius of 1,860,000 km. A million or so kilometers might seem like a lot, but when you consider the sun is 1,391,000 km in diameter (695,500km radius), 1.8m km starts to look really close. At closest approach then, ISON was only 1,165,000km from the surface of the sun.
For comparison, Mercury’s orbital radius of 58m KM and Venus’ orbit is 108m km. The Earth is on average 150m km from the sun.