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The Sodium Tails of Near-Sun Comets

Author: Geraint Jones

MSSL, UCL & Centre for Planetary Sciences at UCL/Birkbeck

Co-Authors: H. Osborn (Dept. of Earth Sciences, UCL), Y. Ramanjooloo (MSSL, UCL & Centre for Planetary Sciences at UCL/Birkbeck)

Session: PL1: Small bodies in Our Solar System

Presentation type: Poster      Poster Session A   


In 1997, comet C/1995 O1 (Hale-Bopp) was found to possess a tail composed of sodium atoms accelerated anti-sunward by radiation pressure. Although sodium had long been known to exist in comets, a distinct tail had only been reported in one other comet, in 1957. Sodium is a very strong contributor to the emission spectra of sungrazing comets. Although it is known that there are at least two sodium sources, one near the nucleus, and the other in the extended dust tail, the ultimate sources of the sodium have not been identified. We present results of our survey of several sodium tails observed by the ESA/NASA Solar and Heliospheric Observatory spacecraft’s LASCO coronagraph, reporting on their morphologies and brightness. We present our initial simulations of the tails; their modelling is complicated by the fact that the acceleration of sodium atoms is a strong function of the atoms’ radial velocity, due to the dependence of the acceleration on the strength of the Doppler-shifted Fraunhofer sodium absorption lines in the atoms’ frame of reference. We discuss the implications our results for our understanding of near-Sun comets’ composition and origins.

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