Preprint typeset using LATEX style emulateapj v. 08/22/09 DISINTEGRATION OF COMET C/2012 S1 (ISON) SHORTLY BEFORE PERIHELION: EVIDENCE FROM INDEPENDENT DATA SETS

As an Oort Cloud object with a record small perihelion distance of 2.7 R and discovered more than a year before its encounter with the Sun, comet C/2012 S1 is a subject of considerable scientific in-terest. 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 amor-phous 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 R, 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