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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 31, issue 10
Ann. Geophys., 31, 1673–1679, 2013
https://doi.org/10.5194/angeo-31-1673-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.
Ann. Geophys., 31, 1673–1679, 2013
https://doi.org/10.5194/angeo-31-1673-2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Regular paper 08 Oct 2013

Regular paper | 08 Oct 2013

On the supply of heavy planetary material to the magnetotail of Mercury

D. C. Delcourt D. C. Delcourt
  • LPP, Ecole Polytechnique-CNRS-UPMC, Saint-Maur des Fossés, France

Abstract. We examine the transport of low-energy heavy ions of planetary origin (O+, Na+, Ca+) in the magnetosphere of Mercury. We show that, in contrast to Earth, these ions are abruptly energized after ejection into the magnetosphere due to enhanced curvature-related parallel acceleration. Regardless of their mass-to-charge ratio, the parallel speed of these ions is rapidly raised up to ~ 2 VE × B (denoting by VE × B the magnitude of the local E × B drift speed), in a like manner to Fermi-type acceleration by a moving magnetic mirror. This parallel energization is such that ions with very low initial energies (a few tenths of eVs) can overcome gravity and, regardless of species or convection rate, are transported over comparable distances into the nightside magnetosphere. The region of space where these ions reach the magnetotail is found to extend over altitudes similar to those where enhanced densities are noticeable in the MESSENGER data, viz., from ~ 1000 km up to ~ 6000 km in the pre-midnight sector. The observed density enhancements may thus follow from E × B related focusing of planetary material of dayside origin into the magnetotail. Due to the planetary magnetic field offset, an asymmetry is found between drift paths anchored in the Northern and Southern hemispheres, which puts forward a predominant role of heavy material originating in the Northern Hemisphere in populating the innermost region of Mercury's magnetotail.

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