The Early Inbound Activity of Comet ISON (C/2012 S1)
Abstract
We have assembled a variety of data on the early behavior of comet ISON through early June 2013, including V magnitudes from the ground and from spacecraft (SWIFT, DIFlyby), upper limits on gas from the DIFlyby, Herschel, and Hubble, and ground-based detections of CO and CN. We argue that the comet’s activity was steadily increasing from the pre-discovery observations in 2011 through late 2012. The activity then flattened and remained constant until January 2013, at which point it started to decrease and continued decreasing until earliest June. We interpret this in the classical picture (e.g., Whipple 1978 Moon and Planets 18, 343) of a dynamically new comet from the Oort cloud having a totally irradiated crust of order 3-10 meters thick from 4.5 billion years of galactic cosmic rays outside the heliosphere. The irradiated layer is released at very large distances due to the presence of free radicals and other chemically active species. As this crust is depleted the activity decreases and in early June we are awaiting the onset of “normal” cometary activity, which should be detected by fall at the latest.
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #45
- Pub Date:
- October 2013
- Bibcode:
- 2013DPS....4540704A