Cometary ions detected by the Cassini spacecraft 6.5 au downstream of Comet 153P/Ikeya-Zhang

TL;DR

This paper reports the detection of cometary ions by Cassini at 6.5 au, revealing the longest measured cometary ion tail, and discusses the ionization process and solar wind interactions during the comet's passage.

Contribution

It presents the first measurement of a cometary ion tail at such a large distance, demonstrating the extent of comet-solar wind interactions.

Findings

Detection of enhanced pickup proton flux at 6.5 au

Longest measured cometary ion tail (>7.5 au)

Implication of cometary ionization and solar wind modulation

Abstract

During March-April 2002, while between the orbits of Jupiter and Saturn, the Cassini spacecraft detected a significant enhancement in pickup proton flux. The most likely explanation for this enhancement was the addition of protons to the solar wind by the ionization of neutral hydrogen in the corona of comet 153P/Ikeya-Zhang. This comet passed relatively close to the Sun-Cassini line during that period, allowing pickup ions to be carried to Cassini by the solar wind. This pickup proton flux could have been further modulated by the passage of the interplanetary counterparts of coronal mass ejections past the comet and spacecraft. The radial distance of 6.5 Astronomical Units (au) traveled by the pickup protons, and the implied total tail length of >7.5 au make this cometary ion tail the longest yet measured.