New studies released at the American Astronomical Society’s 45th Annual Division for Planetary Sciences meeting in Denver, Colorado suggests that Comet ISON could make it through its close perihelion passage near the Sun.
The first criterion for ISON to survive perihelion is its nucleus size. Comet nuclei smaller than 200 meters in diameter, with an average density or lower typically do not survive a close passage to the Sun. Observations from the Hubble Space Telescope, as well as smaller telescopes, suggest that ISON is between 1 and 4 kilometers across..
ISON may be just big and dense enough not to be vaporized and to survive its close encounter with the Sun. So it looks like ISON appears likely to survive the combination of mass loss due to sublimation and tidal disruption for most plausible scenarios.
ISON will pass inside the Roche limit of the Sun, which is a distance of 2.4 million kilometers with temperatures approaching 5,000 degrees Fahrenheit on closest approach. Comet ISON is expected to be the most active and put on its best showing post-perihelion – if it survives.