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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 20, issue 1
Ann. Geophys., 20, 1–11, 2002
© Author(s) 2002. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 20, 1–11, 2002
© Author(s) 2002. This work is distributed under
the Creative Commons Attribution 3.0 License.

  31 Jan 2002

31 Jan 2002

Plasma and wave phenomena induced by neutral gas releases in the solar wind

H. Laakso1, R. Grard1, P. Janhunen2, and J.-G. Trotignon3 H. Laakso et al.
  • 1ESA Space Science Department, Noordwijk, The Netherlands
  • 2Finnish Meteorological Institute, Geophysics Research, Helsinki, Finland
  • 3LPCE, CNRS, Orleans, France
  • Correspondence to: H. Laakso (

Abstract. We investigate plasma and wave disturbances generated by nitrogen (N2) gas releases from the cooling system of an IR-camera on board the Vega 1 and Vega 2 spacecraft, during their flybys of comet Halley in March 1986. N2 molecules are ionized by solar UV radiation at a rate of ~ 7 · 10-7 s-1 and give rise to a plasma cloud expanding around the spacecraft. Strong disturbances due to the interaction of the solar wind with the N+2 ion cloud are observed with a plasma and wave experiment (APV-V instrument). Three gas releases are accompanied by increases in cold electron density and simultaneous decreases of the spacecraft potential; this study shows that the spacecraft potential can be monitored with a reference sensor mounted on a short boom. The comparison between the model and observations suggests that the gas expands as an exhaust plume, and approximately only 1% of the ions can escape the beam within the first meters. The releases are also associated with significant increases in wave electric field emission (8 Hz–300 kHz); this phenomenon lasts for more than one hour after the end of the release, which is most likely due to the temporary contamination of the spacecraft surface by nitrogen gas. DC electric fields associated with the events are complex but interesting. No magnetic field perturbations are detected, suggesting that no significant diamagnetic effect (i.e. magnetic cavity) is associated with these events.

Key words. Ionosphere (planetary ionosphere) – Space plasma physics (active perturbation experiments; instruments and techniques)

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