Hubble Space Telescope Pre-Perihelion ACS/WFC Imaging Polarimetry of Comet ISON (C/2012 S1) at 3.81 AU
Abstract
We present the first polarization images of Comet ISON (C/2012 S1) taken with the Hubble Space Telescope (HST) on UTC 2013 May 8 (r = 3.81 AU, delta = 4.34 AU), when the phase angle was α ≈ 12.25 degrees. Although this phase angle is approximately centered in the negative polarization branch, there is no evidence of a negative polarization circumnucleus halo region that has been observed in previous polarimetric images of Kuiper-belt comets. Instead, the central region 0.32 arcseconds ≈ 1000 km) of the image shows a polarization p ~ 2.0 - 2.5% that is approximately perpendicular to the scattering plane. Such positive polarization has been observed previously as a characteristic feature of cometary jets. The region beyond 1000 km, with sufficient signal-to-noise to make a polarization measurement (≤ 5000 km), shows a negative polarization p ~ 1.8% that varies only slightly.
- Publication:
-
AAS/Division for Planetary Sciences Meeting Abstracts #45
- Pub Date:
- October 2013
- Bibcode:
- 2013DPS....4541310H