  [Abridged] Sun-grazing comets almost never re-emerge, but their sublimative
destruction near the sun has only recently been observed directly, while
chromospheric impacts have not yet been seen, nor impact theory developed.
Employing simple analytic models to describe comet destruction near the Sun and
to enable the estimation of observable signatures, we find analytic solutions
for the mass as a function of distance from the Sun, for insolation
sublimation, impact ablation and explosion. Sun-grazers are found to fall into
three regimes based on initial mass and perihelion: sublimation-, ablation-,
and explosion-dominated. Most sun-grazers are destroyed sublimatively, and our
analytic results are similar to numerical models. Larger masses (>10^11g) with
small perihelion (q<1.01Rsun) ablation dominates but results are sensitive to
nucleus strength, Pc, and entry angle to the vertical, phi.
  Nuclei with initial mass >~10^10g (Pc/10^6 (dyne/cm^2) sec (phi))^3 are fully
ablated before exploding, though the hot wake itself explodes. For most
sun-impactors sec(phi)~1. For small perihelion the ablation regime applies to
moderate masses ~10^13-16 g impactors unless Pc is very low. For higher masses,
or smaller perihelia, nuclei reach higher densities where ram pressure causes
catastrophic explosion. For perihelion < 1.01Rsun, initial mass > 10^11 g
nuclei are destroyed by ablation or explosion (depending on phi and Pc) in the
chromosphere, producing flare-like events with cometary abundance spectra. For
all plausible masses and physical parameters, nuclei are destroyed above the
photosphere.

Solar and Stellar Astrophysics;Earth and Planetary Astrophysics