Since its discovery in September 2012, Comet ISON has been a bit of a puzzle. At first, the comet was considered unusually bright because it was spotted by astronomers far beyond Jupiter’s orbit, raising the prospect that it might be visible on Earth even in daylight.
However, later observations showed the comet was not brightening as much as predicted as it moved closer to the sun. Heating from the sun vaporizes ices in the comet’s body, creating a long, glowing tail....
If it survives, calculations show Comet ISON will be bumped out of the solar system after its swing around the sun.
The comet is named for the International Scientific Optical Network, or ISON, located near Kislovodsk, Russia, which made the first observation of the comet."
Meanwhile, evidence for an Earth impacting comet has been found in the Egyptian desert. Only a pebble dubbed Hypatia is known to have survived. http://www.sci-news.com/space/science-libyan-desert-glass-diamond-bearing-pebble-evidence-comet-01446.html