The Characteristics and Evolution of the Dust Coma of Comet C/2012 S1 (ISON)
Abstract
C/2012 S1 (ISON) is a dynamically new comet with a sungrazing perihelion only 1.7 solar radii from the Sun's surface, which makes it unique among the known comets. The discovery of C/ISON in September 2012 at a heliocentric distance of ~6 AU is more than one year before its perihelion in November 2013, allowing a detailed characterization as the comet moves from the frigid conditions of the outer solar system to extreme heating during its close passage near the Sun. As part of an international observing campaign, the Hubble Space Telescope (HST) imaged the comet in multiple epochs from April to October 2013 pre-perihelion to characterize its dust coma at 4.15, 3.78, and 1.50 AU. We report on our analysis of these HST images, including the dust production rate, the dust coma colors and morphology, and the rotation pole of the nucleus. The first two epochs of observations showed that C/ISON displays a color variations in its dust coma within ~5000 km from the nucleus that is best explained by the existence and sublimation of water ice grains. The pole orientation, as measured from the sunward jet, suggests a high obliquity, and indicates that the nucleus of C/ISON always faces the Sun with one hemisphere until about a week before the perihelion. We will use the observations in October to search for any evolutionary changes in the coma, and to refine the determination of the rotation pole.
- Publication:
-
American Astronomical Society Meeting Abstracts #223
- Pub Date:
- January 2014
- Bibcode:
- 2014AAS...22321806L