  As an Oort Cloud object with a record small perihelion distance of 2.7 Rsun
and discovered more than a year before its encounter with the Sun, comet C/2012
S1 is a subject of considerable scientific interest. Its activity along the
orbit's inbound leg evolved through a series of cycles. Two remarkable events
preserved in SOHO's and/or STEREO's near-perihelion images of its tail were an
early massive production of gravel at heliocentric distances of up to ~100 AU,
evidently by the annealing of amorphous water ice on and near the nucleus'
surface; and, about a week before perihelion, a rapid series of powerful
explosions, from the comet's interior, of water with dust at extremely high
rates, causing precipitous fragmentation of the nucleus, shattering it into a
vast number of sublimating boulders, and ending up, a few days later, with a
major, sudden drop in gas emission. The disintegration of the comet was
completed by about 3.5 hours before perihelion, at a heliocentric distance of
5.2 Rsun, when C/2012 S1 ceased to exist as an active comet. The orbital motion
in this period of time was subjected to progressively increasing
outgassing-driven perturbations. A comprehensive orbital analysis results in
successfully fitting the comet's observed motion from 2011 to ~7 hours before
perihelion.
