  On 2013 November 28 Comet ISON (C/2012 S1) will pass by the Sun with a
perihelion distance of 2.7 solar radii. Understanding the possible outcomes for
the comet's response to such a close passage by the Sun is important for
planning observational campaigns and for inferring ISON's physical properties.
We present new numerical simulations and interpret them in context with the
historical track record of comet disruptions and of sungrazing comet behavior.
Historical data suggest that sizes below ~200 m are susceptible to destruction
by sublimation driven mass loss, while we find that for ISON's perihelion
distance, densities lower than 0.1 g cm^-3 are required to tidally disrupt a
retrograde or non-spinning body. Such low densities are substantially below the
range of the best-determined comet nucleus densities, though dynamically new
comets such as ISON have few measurements of physical properties. Disruption
may occur for prograde rotation at densities up to 0.7 g cm^-3, with the
chances of disruption increasing for lower density, faster prograde rotation,
and increasing elongation of the nucleus. Given current constraints on ISON's
nucleus properties and the typically determined values for these properties
among all comets, we find tidal disruption to be unlikely unless other factors
(e.g., spin-up via torquing) affect ISON substantially. Whether or not
disruption occurs, the largest remnant must be big enough to survive subsequent
mass loss due to sublimation in order for ISON to remain a viable comet well
after perihelion.
