title: Cometary science. Birth of a comet magnetosphere: a spring of water ions.
abstract: The Rosetta mission shall accompany comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 astronomical units through perihelion passage at 1.25 astronomical units, spanning low and maximum activity levels. Initially, the solar wind permeates the thin comet atmosphere formed from sublimation, until the size and plasma pressure of the ionized atmosphere define its boundaries: A magnetosphere is born. Using the Rosetta Plasma Consortium ion composition analyzer, we trace the evolution from the first detection of water ions to when the atmosphere begins repelling the solar wind (~3.3 astronomical units), and we report the spatial structure of this early interaction. The near-comet water population comprises accelerated ions (<800 electron volts), produced upstream of Rosetta, and lower energy locally produced ions; we estimate the fluxes of both ion species and energetic neutral atoms.
authors.affiliation: Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden. Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Rymdcampus 1, 981 28 Kiruna, Sweden. hans.nilsson@irf.se.
authors.forename: Hans
authors.initials: H
authors.lastname: Nilsson
authors.affiliation: Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
authors.forename: Gabriella
authors.initials: G
authors.lastname: Stenberg Wieser
authors.affiliation: Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden. Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Rymdcampus 1, 981 28 Kiruna, Sweden.
authors.forename: Etienne
authors.initials: E
authors.lastname: Behar
authors.affiliation: Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering, Post Office Box 13000, FI-00076 Aalto, Finland.
authors.forename: Cyril Simon
authors.initials: CS
authors.lastname: Wedlund
authors.affiliation: Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Brussels, Belgium.
authors.forename: Herbert
authors.initials: H
authors.lastname: Gunell
authors.affiliation: Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Yamauchi
authors.affiliation: Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
authors.forename: Rickard
authors.initials: R
authors.lastname: Lundin
authors.affiliation: Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
authors.forename: Stas
authors.initials: S
authors.lastname: Barabash
authors.affiliation: Swedish Institute of Space Physics, Post Office Box 812, 981 28 Kiruna, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Wieser
authors.affiliation: Imperial College London, Exhibition Road, London SW7 2AZ, UK.
authors.forename: Chris
authors.initials: C
authors.lastname: Carr
authors.affiliation: Imperial College London, Exhibition Road, London SW7 2AZ, UK.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Cupido
authors.affiliation: Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, USA.
authors.forename: James L
authors.initials: JL
authors.lastname: Burch
authors.affiliation: Institut de Recherche en Astrophysique et Planétologie, Toulouse, France.
authors.forename: Andrei
authors.initials: A
authors.lastname: Fedorov
authors.affiliation: Institut de Recherche en Astrophysique et Planétologie, Toulouse, France.
authors.forename: Jean-André
authors.initials: JA
authors.lastname: Sauvaud
authors.affiliation: Department of Physics, University of Helsinki, Post Office Box 64, FI-00014 Helsinki, Finland. Finnish Meteorological Institute, Post Office Box 503, FI-00101 Helsinki, Finland.
authors.forename: Hannu
authors.initials: H
authors.lastname: Koskinen
authors.affiliation: Aalto University, School of Electrical Engineering, Department of Radio Science and Engineering, Post Office Box 13000, FI-00076 Aalto, Finland. Finnish Meteorological Institute, Post Office Box 503, FI-00101 Helsinki, Finland.
authors.forename: Esa
authors.initials: E
authors.lastname: Kallio
authors.affiliation: Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), UMR 7328 CNRS-Université d'Orléans, France.
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Lebreton
authors.affiliation: Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, Sweden.
authors.forename: Anders
authors.initials: A
authors.lastname: Eriksson
authors.affiliation: Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, Sweden.
authors.forename: Niklas
authors.initials: N
authors.lastname: Edberg
authors.affiliation: Belgian Institute for Space Aeronomy, Avenue Circulaire 3, 1180 Brussels, Belgium.
authors.forename: Raymond
authors.initials: R
authors.lastname: Goldstein
authors.affiliation: Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), UMR 7328 CNRS-Université d'Orléans, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Henri
authors.affiliation: Technicsche Universität-Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Mendelssohnstraße 3, D-38106 Braunschweig, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Koenders
authors.affiliation: Southwest Research Institute, 6220 Culebra Road, San Antonio, TX 78238, USA.
authors.forename: Prachet
authors.initials: P
authors.lastname: Mokashi
authors.affiliation: Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest, Hungary.
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Nemeth
authors.affiliation: Technicsche Universität-Braunschweig, Institute for Geophysics and Extraterrestrial Physics, Mendelssohnstraße 3, D-38106 Braunschweig, Germany.
authors.forename: Ingo
authors.initials: I
authors.lastname: Richter
authors.affiliation: Wigner Research Centre for Physics, 1121 Konkoly Thege Street 29-33, Budapest, Hungary.
authors.forename: Karoly
authors.initials: K
authors.lastname: Szego
authors.affiliation: Space Research Institute, Austrian Academy of Sciences, Schmiedlstraße 6, 8042 Graz, Austria.
authors.forename: Martin
authors.initials: M
authors.lastname: Volwerk
authors.affiliation: Rosetta Science Ground Segment, Science and Robotic Exploration (SRE-OOR), Office A006, European Space Astronomy Centre, Post Office Box 78, 28691 Villanueva de la Cañada, Madrid, Spain.
authors.forename: Claire
authors.initials: C
authors.lastname: Vallat
authors.affiliation: Physikalisches Institut, University of Bern, Sidlerstraße 5, CH-3012 Bern, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Rubin