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We present the results of a global coma morphology campaign for comet C/2012S1 (ISON), which was organized to involve both professional and amateurobservers. In response to the campaign, many hundreds of images, from nearlytwo dozen groups were collected. Images were taken primarily in the continuum,which help to characterize the behavior of dust in the coma of comet ISON. Thecampaign received images from January 12 through November 22, 2013 (an intervalover which the heliocentric distance decreased from 5.1 AU to 0.35 AU),allowing monitoring of the long-term evolution of coma morphology during thepre-perihelion leg of comet ISON. Data were contributed by observers spreadaround the world, resulting in particularly good temporal coverage duringNovember when comet ISON was brightest but its visibility was limited from anyone location due to the small solar elongation. We analyze the northwesternsunward continuum coma feature observed in comet ISON during the first half of2013, finding that it was likely present from at least February through May anddid not show variations on diurnal time scales. From these images we constrainthe grain velocities to ~10 m/s, and we find that the grains spent 2-4 weeks inthe sunward side prior to merging with the dust tail. We present a rationalefor the lack of continuum coma features from September until mid-November 2013,determining that if the feature from the first half of 2013 was present, it waslikely too small to be clearly detected. We also analyze the continuum comamorphology observed subsequent to the November 12 outburst, and constrain thefirst appearance of new features in the continuum to later than November 13.99UT.

Results from the Worldwide Coma Morphology Campaign for Comet ISON (C/2012 S1)