1,3,4,6,2,- 1Universite de Toulouse, CNRS, CNES, IRAP, Toulouse, France
- 2Physics Department, University of New Brunswick, Fredericton, Canada
- 3Institute of Physics, University of Graz, Austria
- 4IAFE/CONICET, University of Buenos Aires,Ciudad Aut´onoma de BuenosAires, Argentina
- 5Center for Space Physics and Department of Astronomy, Boston University, Boston, MA, USA
- 6Department of Astronomy, University of Maryland, College Park, MD, USA
- 7Planetary Magnetospheres Laboratory, NASA Goddard Space Flight Center, Greenbelt, MD, USA
- 9Space Sciences Laboratory, University of California, Berkeley, USA
- 10Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA
Electromagnetic waves at the local proton cyclotron frequency are frequently observed upstream from the Martian bow shock. They are excited by unstable velocity distributions of newborn protons continuously produced locally by ionization of exospheric hydrogen atoms (pickup protons). The analysis of MAVEN magnetic field data demonstrates for the first time that the amplitude of these waves undergo a sharp change when crossing the electron foreshock boundary. Moreover, a decrease of the amplitude with the increasing distance from the shock along the ambient average magnetic field is observed inside the foreshock. Both signatures are correlated with the variations of the energetic electron fluxes. These two properties connecting the wave growth to electron physics raise an issue since the waves are excited purely through an ion-ion instability. We propose that the extra free energy necessary to increase the wave amplitude is due to additional ionization of hydrogen atoms by electron impact ionization inside the foreshock. These results imply that extreme caution is needed when directly deriving the exospheric density at Mars and other similar environments from the local pickup ion wave amplitude, especially in the foreshock region.
How to cite: Mazelle, C., Meziane, K., Simon-Wedlund, C., Bertucci, C., Zhang, C., Romanelli, N., Fruchtman, J., Hamza, A., Halekas, J. S., Espley, J. R., Mitchell, D. L., and Curry, S.: Effect of Foreshock Electron Impact Ionization on the Amplitude of Pickup Proton Driven Waves: Implication for Exosphere Density Estimates, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-1042, https://doi.org/10.5194/epsc2026-1042, 2026.
