DFG-RSF: Verlust der Mars Atmosphäre durch Sonnenwind Erosion - Theorie und koordinierte Beobachtungen durch Mars Express und MAVEN
Zusammenfassung der Projektergebnisse
The ion losses from the Mars atmosphere caused by solar wind scavenging are the fundamental question addressed in this project. Multi-instrument observations from two spacecraft (MaRS, ASPERA-3, and MARSIS onboard Mars Express and the Plasma Package onboard MAVEN) were used in this project. The project has been divided in six objectives: (i) Ion losses in dependence of the variations of the solar extreme ultraviolet radiation (EUV). It was shown that fluxes of oxygen ions with energy E > 30 eV both inside and outside of the Martian magnetosphere are not sensitive to solar EUV variations. In contrast, the fluxes of lost ions with energies <30 eV significantly increase with increasing solar irradiance. It is concluded that the different response to the solar irradiance between the low and high energy ions is caused by thermal energy ions that are extracted by the ambipolar electric field, i.e. by the ionospheric pressure gradient which is positively correlated with the EUV flux. (ii) Ion losses in dependence of solar wind variations. We have identified three different channels through which the ionospheric plasma is able to escape from the Mars atmosphere. The low-energy ion component, which mainly occupies the lobes in the magnetospheric tail, is partly driven by the ambipolar electric field caused by the expansion of the ionospheric electrons along the field lines. Fluxes of low-energy oxygen ions in the tail decrease with an increase of the solar wind dynamic pressure. Higher energy ions occupy the plasma sheet and the boundary layer in the tail. These ions are accelerated by the jxB forces related to the magnetic field tensions in the induced magnetosphere. (iii) Ion losses as a function of IMF variations. The transport motions driven by the magnetic field pressure and field tensions are intensified by an increase of the induced magnetic field strength. The local ion densities at the dayside decrease considerably. A different trend is observed at the nightside. The ion density in the nightside ionosphere above the northern lowlands is higher than in the southern hemisphere indicating that the plasma transport from the dayside is the main source of the nightside ionosphere. The ion density in the upper ionosphere depends on the field geometry. In those areas where the role of the crustal magnetic field is small, the ion density strongly decreases for a strong horizontal orientation of the magnetic field implying the scavenging of plasma by the magnetic field tensions. (iv) Structure and dynamics of the Martian ionosphere. A clear correlation between the solar EUV and vertical total electron content (TEC) was observed. A flexible 1-D ionospheric model was developed, which recreates the electron density profiles using the Mars Climate Database (MCD) atmospheric model, the photoionization and secondary impact ionization cross-sections. The comparison between the observed electron density profiles and the simulated profiles is in good agreement. (v) The role of the crustal magnetic fields to the ion losses. The ion density in the upper ionosphere responds strongly to the presence of crustal magnetic fields. The ion density in the ionosphere over the ‘magnetized ‘areas is significantly higher than in the regions without or with a very weak crustal field. Crustal magnetic fields attenuate significantly the motion of the ionospheric ions and increase the flux of returning ions. On the other hand, the net escape fluxes from the "magnetized" ionosphere remains vital since the ion densities in the ionosphere with strong crustal fields are significantly higher than in the ionosphere with weak crustal magnetic fields. The crustal magnetic field also leads to the expansion of the ionosphere and the increase of the area exposed to the solar wind. As a result, fluxes from higher altitudes essentially contribute to the flow pattern in the Martian tail producing an excess of ion losses of about 15% throughout the southern part of the tail. (vi) The space weather near Mars and the ion losses during strong solar events (CME, CIR, SEP). We have studied the consequences of the impact of the ICME on Mars on 13 September 2017. During this event the ionosphere strongly shrinks down to ~ 400 km without a visible effect of compression at low altitudes. This implies that the upper portion of the ionosphere might be lost during the ICME impact.
Projektbezogene Publikationen (Auswahl)
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Effects of solar irradiance on the upper ionosphere and oxygen ion escape at Mars: MAVEN observations, Solar Irradiance as a Driver for Ion Escape at Mars, J. Geophys. Res. Space Physics, 122, 2017
Dubinin E., M. Fraenz, M. Pätzold, J. McFadden, P. R. Mahaffy, F. Eparvie, J. S. Halekas, J. E. P. Connerney, D. Brain, B. M. Jakosky, O. Vaisberg, and L. Zelenyi
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Martian ionosphere observed by Mars Express. 2. Influence of solar irradiance on upper ionosphere and escape fluxes, Planetary and Space Science, 145,1–8, 2017
Dubinin E., M. Fraenz, M. Pätzold, D. Andrews, O. Vaisberg, L. Zelenyi, and S. Barabash
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The Effect of Solar Wind Variations on the Escape of Oxygen Ions From Mars Through Different Channels: MAVEN Observations, Journal of Geophysical Research (Space Physics) 122, 11,285–11,301. 2017
Dubinin, E. et al.
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Small scale disturbances in the lower dayside ionosphere of Mars as seen by the MaRS radio science experiment on Mars Express. Dissertation, Universität zu Köln, 2018
Peter, K.
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(2019), Expansion and shrinking of the martian topside ionosphere, Journal of Geophysical Research: Space Physics, 24
Dubinin, E., Fraenz, M., Pätzold, M., Woch, J., McFadden, J., Halekas, J. S., et al.
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(2019). The induced magnetosphere of Mars: Asymmetrical topology of the magnetic field lines. Geophysical Research Letters, 46
Dubinin, E., Modolo, R., Fraenz, M., Pätzold, M., Woch, J., Chai, L., Y.Wei, J.E.P.Connerney, J. Mcfadden, G.DiBraccio, J.Espley, E.Grigorenko, and L.Zelenyi
