Martian hydrogen exosphere charge exchange with solar wind

Abstract

[1] Charge exchange of solar wind with the Martian exosphere has been shown to play a crucial role in the formation of the magnetic pileup boundary observed by Mars Global Surveyor. However, the question of how the Martian exospheric structure is quantitatively altered by charge exchange of the solar wind remains open. To answer this question, a three-dimensional Monte Carlo exosphere model was developed. In this model the effects of planetary rotation, photoionization, Lyman a scattering, and charge exchange with the solar wind are included. Although the change of exospheric density profile is indistinctive, simulation results show that the existence of the hot atomic hydrogen population produced by charge exchange alters the exospheric temperature structure greatly and the symmetry of the exospheric structure is totally destroyed at high altitude. Another noticeable phenomenon is that charge exchange and Lyman a scattering combine to make the nightside exosphere be cooler than and expand more slowly than the ambient exosphere. In the end we use our simulation results to estimate the contribution of the hot component to Ly a emission. Furthermore, output of our model can be used to predict particle observations made by future missions to Mars.

Effect of the Lateral Exospheric Transport on the Horizontal Hydrogen Distribution Near the Exobase of Mars

“…For current solar conditions, this frequency, rescaled to the Sun‐Mars distance, is between 0.3 and 0.8 × 10 −7 s −1 and therefore the typical lifetime of an exospheric hydrogen atom is >115 days. The charge exchange ionization frequency estimated by Chen and Cloutier () is at most 1 order of magnitude larger (~5 × 10 −7 s −1 ), consistent with the escape rate ratio of H + produced by charge exchange and photoionization computed by Modolo et al (). This ionization frequency leads to a lifetime of ~20 days.…”

A rapid decrease of the hydrogen corona of Mars

“…The model applies a Chamberlain model for the density of H atoms above the exobase, excluding satellite particles. This approach was verified by Monte Carlo modeling by Chen and Cloutier [2003], who found that this approach accounts best for exosphere changes due to charge exchange with solar wind protons. The hydrogen density below the exobase is derived from the resolution of the diffusion equation for atomic hydrogen through a CO 2 atmosphere [Chaufray et al, 2008].…”

Observations of low‐frequency magnetic oscillations in the Martian magnetosheath, magnetic pileup region, and tail

“…However, the addition of a relatively small density of heavier ions causes the growth rate of the proton cyclotron instability to be significantly decreased and thereby allows the mirror instability to become the dominant mode in an anisotropic plasma [ Price et al , 1986]. Such a situation occurs in the Martian magnetosheath since the relatively large exosphere has been calculated to extend out to magnetosheath altitudes [e.g., Chen and Cloutier , 2003].…”