Evidence of electron impact ionization in the magnetic pileup boundary of Mars

Abstract

Abstract. A sharp decline in electron fluxes is observed in the Mars Global Surveyor Electron Reflectometer data in conjunction with the magnetic pileup boundary. We examine the characteristics of the evolution of the electron distribution function for one orbit. We determine that the spectra can best be explained by electron impact ionization of oxygen and hydrogen. To reproduce the observed spectral evolution, we construct a model of the effects of electron impact ionization on the electron distribution function as a flow element encounters the neutral atmosphere. Using the observed post-shock electron distribution function, we are able to reproduce the observed flux attenuation. We conclude that electron impact ionization is the physical mechanism responsible for the spectral feature.

The Induced Magnetospheres of Mars, Venus, and Titan

“…At the same time, 40 eV electron fluxes fall from 2 × 10 6 to 2 × 10 5 s −1 cm −2 sr −1 eV −1 . This decrease is smaller but still noticeable for higher energies in agreement with the predicted cross section for electron impact ionization (Crider et al 2000). As it will be shown later, this does not imply a decrease of the total electron density but an increase, followed by a decrease of the fluxes of superthermal electrons.…”

The magnetic field draping direction at Mars from April 1999 through August 2004

“…Based on this idea, a method for identifying time periods when MGS was in or above the MPB was developed by Brain et al (2005). In this study, the authors searched the MGS mapping data for a population of energized 100 eV electrons, which are created at the bow shock but lost to electron impact ionization or plasma depletion in the vicinity of the MPB (Crider et al, 2000;Øieroset et al, 2004). The presence of this population indicates that the spacecraft is between the bow shock and MPB.…”

Plasma Flow and Related Phenomena in Planetary Aeronomy

“…Simultaneously, the electron fluxes measured by the electron reflectometer (ER) attenuate in a manner consistent with electron impact ionization of the oxygen and hydrogen exosphere by solar wind electrons (Crider et al 2000). Coincident with this location, wave activity in the MAG data declines with decreasing altitude.…”

“…In this region, the magnetic field lines frozen into the electron gas follow the denser and cooler plasma. This is a consequence of the mass loading and ionization mechanisms, which contribute to the dominance of heavy ions of exospheric origin (Lundin et al 1990;Crider et al 2000). The lower limit of this region is the final planetary obstacle (Luhmann 1986;Mitchell et al 2001).…”