Fine-scale structure in cometary dust tails I: Analysis of striae in Comet C/2006 P1 (McNaught) through temporal mapping

Oliver Price,Geraint H Jones,Jeff Morrill,Mathew Owens,Karl Battams,Huw Morgan,Miloslav Drückmuller,Sebastian Deiries

doi:10.1016/j.icarus.2018.09.013

Abstract

Striated features, or striae, form in cometary dust tails due to an as-yet unconstrained process or processes. For the first time we directly display the formation of striae, at C/2006 P1 McNaught, using data from the SOHO LASCO C3 coronagraph. The nature of this formation suggests both fragmentation and shadowing effects are important in the formation process. Using the SOHO data with STEREO-A and B data from the HI-1 and HI-2 instruments, we display the evolution of these striae for two weeks, with a temporal resolution of two hours or better. This includes a period of morphological change on 2007 January 13–14 that we attribute to Lorentz forces caused by the comet’s dust tail crossing the heliospheric current sheet. The nature of this interaction also implies a mixing of different sized dust along the striae, implying that fragmentation must be continuous or cascading. To enable this analysis, we have developed a new technique – temporal mapping – that displays cometary dust tails directly in the radiation beta (ratio of radiation pressure to gravity) and dust ejection time phase space. This allows for the combination of various data sets and the removal of transient motion and scaling effects.

Highlights

When active, comets release dust grains of various sizes and morphologies (e.g. Schulz et al, 2015; Hilchenbach et al, 2016)
We present a sequence of images captured by the Large Angle and Spectrometric Coronagraph (LASCO) on the ESA/NASA Solar and Heliospheric Observatory (SOHO) spacecraft, that appears to record clearly for the first time the formation of several striae
We introduce here a new dust tail analysis technique which presents dust features in a consistent way, by morphing images of comets onto a matrix of assumed dust age and sensitivity to solar radiation pressure

Summary

Introduction

Comets release dust grains of various sizes and morphologies (e.g. Schulz et al, 2015; Hilchenbach et al, 2016). Analysis of dust tails’ structure can reveal key information on the dust grains’ parameters, together with the time of release from the nucleus These parameters can in turn provide information on the activity of the nucleus. Features commonly observed in cometary dust (type II) tails include synchronic bands, which are large-scale linear features that are coaligned with the position of the comet’s nucleus, and, much more rarely, striae. The latter are puzzling features that have only been observed in a few, generally very high production rate comets, including C/1957 P1

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