Warm Spitzer Characterization of Comet C/2012 S1 (ISON) : Spitzer Proposal ID #9026

We propose Warm Spitzer photometric imaging DDT observations of Comet ISON, as part of a worldwide observing campaign led by NASA of the comet. Warm Spitzer's 3 and 4 um near-IR passbands will provide unique scattering and emissivity information for the comet's nucleus and dust, and allow us to detect CO_2 gas emission from the comet. Spitzer holds a unique place in the solar system to observe the comet, right before it enters the region of rapid water ice sublimation after spending millions of years in the deep freeze of the Oort Cloud. It is likely the comet will undergo a rapid outburst soon after the time of the proposed observations in the week of June 7 - 14, 2013, and understanding its baseline behavior is critical to understanding the evolution of its activity, as is Spitzer's unique ability to detect CO_2 sublimation and outgassing activity from ISON. As for our previous Spitzer observations of comets Tempel 1 and Hartley 2, we will bootstrap from HST DDT imaging lightcurve and spectroscopic measurements taken over in April - May 2013. The combination of the two datasets will place strong constraints on the comet's coma morphology, and thus its pattern of outgassing jets and the rotation state of the nucleus, and the amount and kind of dust and gas emitted by the comet. Authors : L.Carey et al.