Ramanjooloo, Y; (2015) Comets as natural laboratories: Interpretations of the structure of the inner heliosphere. Doctoral thesis , UCL (University College London).

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Abstract

Comets can be considered to be natural laboratories of the inner heliosphere, as their ion tails trace the solar wind flow. Much has been learnt about the heliosphere’s structure from in situ solar wind spacecraft observations. Their coverage is however limited in time and space. This thesis proposes to address these constraints and ascertain the validity of analysing comets’ ion tails as complementary sources of information on dynamical heliospheric phenomena and the underlying continuous solar wind. Solar wind conditions influence comets’ induced magnetotails, formed through the draping of the heliospheric magnetic field by the velocity shear in the mass-loaded solar wind. I present a novel imaging technique and software to exploit the vast catalogues of amateur and professional images of comet ion tails. My projection technique uses the comet’s orbital plane to sample its ion tail as a proxy for determining radial solar wind velocities in each comet’s vicinity. Making full use of many observing stations from astrophotography hobbyists to professional observatories and spacecraft, this approach is applied to several comets observed in recent years. Complementary velocities, derived from folding ion rays and a velocity profile map built from consecutive images, are provided as an alternative means of quantifying the solar wind-cometary ionosphere interaction. I review the validity of these techniques by comparing near-Earth comets to solar wind models in the inner heliosphere and extrapolated measurements by ACE to a near-Earth comet’s orbit. My radial velocities are mapped back to the solar wind source surface to identify sources of the quiescent solar wind and heliospheric current sheet crossings. Comets are found to be good indicators of solar wind structure, but the quality of results is strongly dependent on the observing geometry. Many ion tails also show a constant curvature, so far unexplained, which further complicates the interpretation of tails’ orientations.

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