title: Interception of comet Hyakutake's ion tail at a distance of 500 million kilometres
abstract: Remote sensing observations and the direct sampling of material from a few comets have established the characteristic composition of cometary gas. This gas is ionized by solar ultraviolet radiation and the solar wind to form 'pick-up' ions, ions in a low ionization state that retain the same compositional signatures as the original gas. The pick-up ions are carried outward by the solar wind, and they could in principle be detected far from the coma (Sampling of pick-up ions has also been used to study interplanetary dust, Venus' tail and the interstellar medium.) Here we report the serendipitous detection of cometary pick-up ions, most probably associated with the tail of comet Hyakutake, at a distance of 3.4 AU from the nucleus. Previous observations have provided a wealth of physical and chemical information about a small sample of comets, but this detection suggests that remote sampling of comet compositions, and the discovery of otherwise invisible comets, may be possible.
authors.affiliation: Department of Physics and Institute for Physical Science and Technology, University of Maryland, College Park 20742, USA. gg10@umail.umd.edu
authors.initials: G
authors.lastname: Gloeckler
authors.initials: J
authors.lastname: Geiss
authors.initials: NA
authors.lastname: Schwadron
authors.initials: LA
authors.lastname: Fisk
authors.initials: TH
authors.lastname: Zurbuchen
authors.initials: FM
authors.lastname: Ipavich
authors.lastname: von Steiger R
authors.initials: H
authors.lastname: Balsiger
authors.initials: B
authors.lastname: Wilken