The effect of energetically produced O₂⁺ on the ion temperatures of the Martian thermosphere

Abstract

In the Martian ionosphere the dominant solar ionization products are O+ and CO2+. These ions are rapidly converted to O2+ by ion neutral reactions resulting in O2+ as the dominant ion. As O2+ has a lower ionization potential, each reaction results in approximately 1.2 eV of energy to be shared by the reaction products. The kinetic energy given to the O2+ will affect the ion temperatures. Calculations have been made of the ion heating rates and temperatures which result from the degradation of these energetic ions for various energy production distributions for conditions similar to those encountered by Viking 1. It is shown that the thermalization of the energetic O2+ can greatly increase the ion temperatures above 200 km compared to those calculated using only the ambient electron heating source. The effect of small horizontal magnetic fields, as predicted by current solar wind interaction models on the ion thermal balance was also investigated. These fields act to restrict the ion thermal conductivity and thus also increase the upper altitude ion temperatures. The combination of the heating by the energetic O2+ and the effect of the magnetic field provide a partial agreement with the Viking 1 measurements.

The Mars thermosphere-ionosphere: Predictions for the arrival of Planet-B

“…This behavior approximates the ion temperatures measured by the RPA on Viking, as presented by Hanson et al (1977). The assumed electron temperature profile is similar to that calculated by Rohrbaugh et al (1979). These assumptions are sufficient for our MT-GCM simulations, since the relevant recombination rates and charge exchange reactions affecting dayside photochemical ions (below 200 km) are only weakly temperature dependent.…”

Mars exospheric thermal and non-thermal components: Seasonal and local variations

“…(1) depends on the electronic temperature, which is not calculated in the LMD-MGCM. Electron temperature model used in this study depends only on the altitude, which is based on the observation by Viking (Hanson and Mantas, 1988) and calculation by Rohrbaugh et al (1979) below 200 km, as also referred by Kim et al (1998).…”

The Plasma Environment of Mars

“…The same model indicated that energy inputs into the ion and electron gases were required at the upper boundary (again presumably associated with the solar wind interaction) in order to obtain agreement with measurements. Other work on the ionospheric energetics has also invoked either energy inputs and/or ionospheric thermal conductivities altered by ionospheric magnetic fields which are induced by the solar wind interaction (see Figure 5.3) (Rohrbaugh et al, 1979;Choi et al, 1998). For example, in the absence of magnetic field effects an input flux of 4 x 10 9 eV cm-2 s-1 is needed for the electrons (Choi et al, 1998).…”