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Magnetosphere of Mars at Almost Radial Interplanetary Magnetic Field.

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Title: Magnetosphere of Mars at Almost Radial Interplanetary Magnetic Field.
Authors: Dubinin, E.1 (AUTHOR) dubinin@mps.mpg.de, Modolo, R.2 (AUTHOR), Fraenz, M.1 (AUTHOR), Pätzold, M.3 (AUTHOR), Tellmann, S.3 (AUTHOR), DiBraccio, G.4 (AUTHOR), Halekas, J.5 (AUTHOR), McFadden, J.6 (AUTHOR), Lin, R.7 (AUTHOR), Huang, S.7 (AUTHOR)
Source: Journal of Geophysical Research. Space Physics. Apr2026, Vol. 131 Issue 4, p1-17. 17p.
Subject Terms: *Geomagnetism, Magnetosphere, Interplanetary magnetic fields, Magnetospheric physics, Plasma flow, Solar wind
Abstract: We have studied the structure of the Martian magnetosphere under conditions of an almost radial interplanetary magnetic field (IMF). Under such conditions, the currents driven by the motional electric field −1cVsw×BIMF ${-}\frac{1}{c}{\mathbf{V}}_{sw}\times {\mathbf{B}}_{\mathit{IMF}}$ are expected to be strongly reduced, and the induced magnetosphere may degenerate. We analyzed Mars Atmosphere and Volatile EvolutioN (MAVEN) data for orbits during which the IMF cone angle was below 20° $20{}^{\circ}$ or larger than 160° $160{}^{\circ}$. We find that the main features of the Martian magnetosphere, observed for the nominal Parker spiral IMF configuration at Mars' orbit, remain present even for nearly field‐aligned plasma flow. The IMF cone angle begins to change at the bow shock, exhibiting large fluctuations but with a clear tendency for the magnetic field lines to envelop the ionospheric obstacle. This process is accompanied by a pileup of the magnetic field and the formation of a magnetic barrier that balances the thermal pressure of the shocked solar wind. Only on very rare orbits do we observe sunward ejection of ions from the ionosphere and their strong interaction with the solar wind. Not a perfect alignment of the IMF and the solar wind flow and the existence of a strong crustal magnetic field are probably responsible for a creation of the magnetosphere even at such a geometry. Plain Language Summary: Mars and Venus have no an intrinsic magnetic field able to stop solar wind. Solar wind interacts directly with their planetary ionospheric shells producing the induced magnetosphere. The electric currents responsible for the formation of the induced magnetosphere are driven by the motional electric field ∼Vsw×BIMF ${\sim} {\mathbf{V}}_{sw}\times {\mathbf{B}}_{\mathit{IMF}}$. However, for almost radial IMF such currents are expected to be strongly reduced and the induced magnetosphere might degenerate. We have analyzed the Mars Atmosphere and Volatile EvolutioN (MAVEN) data for such conditions. It is found that the main features of the Martian magnetosphere, still remain also for almost field‐aligned plasma flow. Key Points: We have analyzed MAVEN data obtained during orbits when the IMF cone angle was below 20 or greater than 160The main features of the nominal Martian magnetosphere remain present even for nearly field‐aligned plasma flowNot a perfect alignment of the IMF and plasma flow and crustal magnetic field are probably responsible for nominal magnetosphere formation [ABSTRACT FROM AUTHOR]
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Abstract:We have studied the structure of the Martian magnetosphere under conditions of an almost radial interplanetary magnetic field (IMF). Under such conditions, the currents driven by the motional electric field −1cVsw×BIMF ${-}\frac{1}{c}{\mathbf{V}}_{sw}\times {\mathbf{B}}_{\mathit{IMF}}$ are expected to be strongly reduced, and the induced magnetosphere may degenerate. We analyzed Mars Atmosphere and Volatile EvolutioN (MAVEN) data for orbits during which the IMF cone angle was below 20° $20{}^{\circ}$ or larger than 160° $160{}^{\circ}$. We find that the main features of the Martian magnetosphere, observed for the nominal Parker spiral IMF configuration at Mars' orbit, remain present even for nearly field‐aligned plasma flow. The IMF cone angle begins to change at the bow shock, exhibiting large fluctuations but with a clear tendency for the magnetic field lines to envelop the ionospheric obstacle. This process is accompanied by a pileup of the magnetic field and the formation of a magnetic barrier that balances the thermal pressure of the shocked solar wind. Only on very rare orbits do we observe sunward ejection of ions from the ionosphere and their strong interaction with the solar wind. Not a perfect alignment of the IMF and the solar wind flow and the existence of a strong crustal magnetic field are probably responsible for a creation of the magnetosphere even at such a geometry. Plain Language Summary: Mars and Venus have no an intrinsic magnetic field able to stop solar wind. Solar wind interacts directly with their planetary ionospheric shells producing the induced magnetosphere. The electric currents responsible for the formation of the induced magnetosphere are driven by the motional electric field ∼Vsw×BIMF ${\sim} {\mathbf{V}}_{sw}\times {\mathbf{B}}_{\mathit{IMF}}$. However, for almost radial IMF such currents are expected to be strongly reduced and the induced magnetosphere might degenerate. We have analyzed the Mars Atmosphere and Volatile EvolutioN (MAVEN) data for such conditions. It is found that the main features of the Martian magnetosphere, still remain also for almost field‐aligned plasma flow. Key Points: We have analyzed MAVEN data obtained during orbits when the IMF cone angle was below 20 or greater than 160The main features of the nominal Martian magnetosphere remain present even for nearly field‐aligned plasma flowNot a perfect alignment of the IMF and plasma flow and crustal magnetic field are probably responsible for nominal magnetosphere formation [ABSTRACT FROM AUTHOR]
ISSN:21699380
DOI:10.1029/2026JA035038