Oxygen ion precipitation in the Martian atmosphere and its relation with the crustal magnetic fields

Abstract

[1] Without a global intrinsic magnetic field, oxygen ions in the Martian atmospheric corona can be picked up by the solar wind directly. The majority of the pickup ions escape, while some can precipitate into the atmosphere, producing sputtering of atmospheric constituents, which may play a significant role in the loss of neutral atmosphere. With its widely distributed crustal magnetic fields, Mars is unique. While it has been shown that Mars's crustal fields can alter the global distribution of escaping ions, little is known about the influence of the crustal fields on the spatial distribution and energy deposition of precipitating pickup ions. In this paper, the global distribution and energy spectrum of the precipitating pickup oxygen ions are calculated using the test particle method in the electric and magnetic fields set up by MHD simulation. Cases of different crustal field conditions are compared to show the influence of the crustal fields on the oxygen ion precipitation. We find, using a test particle code, that the crustal fields likely change the spatial distribution of the precipitation, resulting in irregularly distributed low-energy ion precipitation parches and wide high-energy ion precipitation belts on both the dayside and nightside. The crustal fields increase O + ion precipitation substantially, enhancing energy deposition especially on the nightside. Our results imply that atmospheric sputtering, and accompanying neutral escape, might happen globally and may be enhanced by a factor of almost 2 with the presence of the crustal magnetic fields.

Statistical properties of planetary heavy‐ion precipitations toward the Martian ionosphere obtained from Mars Express

“…The observed precipitating flux is also at the same order of magnitude as the predictions of Li et al []. These are consistent with the predictions by Chaufray et al [] and Li et al []. Our obtained feature in terms of the precipitating location in the MSE coordinate system shown in Figure might also support such previous numerical predictions.…”

“…In our observation, the precipitating PHIs are frequently observed at the low‐SZA region (Figure b). The observed precipitating flux is also at the same order of magnitude as the predictions of Li et al []. These are consistent with the predictions by Chaufray et al [] and Li et al [].…”

“…We also tried to determine the IMF polarity for one event by comparing the ion velocity distribution functions between the MEX/IMA observation and test particle simulations that assumed both polarities. The estimated IMF polarity indicates that the PHI precipitation for that event was likely on the downward electric field hemisphere, supporting the previous numerical predictions [e.g., Luhmann and Kozyra , ; Chaufray et al , ; Li et al , ]. These results indicate that the solar wind electric field (or IMF) orientation might be estimated from the hemisphere where PHIs precipitations are observed, even though the ring ions to estimate the IMF orientation in this study are not detected.…”

“…They found that O + ions with energies of a few tens of eV can only precipitate near the dayside subsolar region [ Chaufray et al , , Figures 6a and 6b], while precipitation flux of high energy (≥500 eV) O + ions in the downward electric field hemisphere is much larger than that in the upward electric field hemisphere, where the solar wind electric field is pointing away from Mars [ Chaufray et al , , Figures 6c and 6d]. Li et al [] also investigated the precipitation patterns of picked‐up O + ions by using the test particle scheme of Fang et al [] under an electromagnetic field from the result of the magnetohydrodynamic (MHD) simulations of Ma et al []. They also demonstrated that the precipitation characteristics obtained by Chaufray et al [] are similar between low‐energy and high‐energy picked‐up O + ions.…”

Statistical studies on Mars atmospheric sputtering by precipitating pickup O+: Preparation for the MAVEN mission

“…Recent studies that included enhanced solar wind, such as the passing of interplanetary coronal mass ejections (ICMEs), solar energetic particle event, or corotating interaction regions (CIRs), suggested that the sputtering effects may significantly increase for short periods due to vary large transient ion precipitation fluxes and energies [ Leblanc et al , ; Hara et al , ; Wang et al , ]. On the other hand, the existence of the surface crustal fields and their various interactions with the IMF can affect the pickup ion escape rates and the precipitation energy and fluxes as well as the resulting sputtering efficiencies [ Ma et al , ; Ma and Nagy , ; Fang et al , ; Li et al , ]. Therefore, an overview of sputtering effects covering a range of Mars environments and related interaction with the solar wind should be studied in more detail to get better estimates of the variability of these effects and their influence on Martian atmosphere evolution.…”