Abstract
The goal of this paper is to understand the processes by which solar wind electrons are energized in the Martian magnetosphere and how this compares to processes at Venus and Earth. Each is unique in the source of its magnetic field topology and how this influences electron energization. To achieve this goal, 24 million spectra spanning 13 years have been examined using the electron spectrometer from the Mars Express spacecraft between about 12,000 km and about 250 km altitude, and from all latitudes and local times. The top 10 largest differential energy flux at energies above the differential energy flux peak have been found: seven spectra from the magnetosheath near noon, three from the dark tail (the largest two from the middle and ionospheric edge of the magnetosheath). Spectral comparisons show a decade range in the peak of the electron distributions; however, all distributions show a similar energy maximum dictated by solar wind/planet interaction. Similarly derived, the largest Venus spectrum occurred near the magnetosheath bow shock and had the same shape as the most intense Mars inner magnetosheath spectrum. The Mars and Venus dayside spectra compared to the Mars nightside spectrum that included an enhanced optical signal attributed to discrete “auroral” precipitation show a similar shape. These spectra are also compared to a selected auroral zone electron spectra from the Earth. The Mars and Venus results suggest that there is no more energy needed to generate electrons forming the nightside precipitation than is gained during the solar wind/planet interaction.
Highlights
The goal of this paper is to understand the processes by which solar wind electrons are energized in the Martian magnetosphere and how this compares to processes at Venus and Earth
The number of electrons may increase to form a localized maximum, indicating a region of larger intensity. If this same spectrum is expressed in terms of the differential energy flux (DEF), the amount of energy carried by these electrons is revealed: Generally, at low energies, there are many electrons that do not carry very much energy, so their DEF is low, and when the energy is very high, each electron carries more energy, but there are fewer electrons resulting again in a low DEF
Even though electrons are more abundant at low energy, they do not carry a significant amount of energy, whereas at high energy, each electron carries a substantial amount of energy, but there are relatively few electrons
Summary
Each planet is unique in the source of its magnetic field topology and how this influences electron energization To achieve this goal, 24 million spectra spanning 13 years with the Mars Express (MEx) spacecraft (Chicarro et al, 2004) have been examined. The spectrum of electrons in the 1 eV to 20 keV energy range in the Mars magnetosphere measured by the MEx spacecraft has the characteristic that the number of electrons decreases with increasing energy, typically showing a change in the slope with an increase in energy. This slope change can be variable, with the exact energy location of where the slope changes, the number of slope changes, and magnitude of the slopes variable as well. There is no Tsyganenko (2002a, 2002b) style magnetic field model available for Mars and Venus that would allow for prediction of where energy is deposited using the continuous slowing-down approximation (Sharber et al, 1996)
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