Comet Ison makes solar approach on Thursday, passing a mere 720,000 miles from the solar surface. It’ll get hot. This could cause a break-up, with fragments then heading on as yet unpredictable trajectories. Could this pose a threat to Earth? Stuart Clark at the Guardian has the following obs:
If it survives an encounter with the sun this week, comet Ison will put on an impressive early morning display in the run-up to Christmas. But anyone hoping for a Bethlehem-style celestial sign on the big day will be disappointed. By then the comet will probably be too faint to see with a naked eye.
Ison is currently speeding towards a fiery encounter on Thursday, which could destroy it. It will pass 720,000 miles above the solar surface, 130 times closer than our planet ever reaches.
The intense sunlight will heat the comet to about 2,700C, speeding up its evaporation. In the past some comets have been seen to vaporise under such an onslaught.