Effects of an Intrinsic Magnetic Field on Ion Escape From Ancient Mars Based on MAESTRO Multifluid MHD Simulations

• Published in: Journal of geophysical research. Space physics 2024-05, Vol.129 (5), p.n/a
• Main Authors: Sakata, R., Seki, K., Terada, N., Sakai, S., Shinagawa, H.
• Format: Article
• Language: English
• Subjects: Aerosols; ancient Mars; Atmosphere; Atmospheric evolution; Carbon dioxide; Charged particles; Climate change; Cobalt; Dipoles; Electric fields; Electromagnetic forces; High altitude; intrinsic magnetic field; ion escape; Ionosphere; Ions; Low altitude; Magnetic fields; Magnetohydrodynamics; Mars; Molecular ions; multifluid MHD simulation; Outflow; Planetary magnetic fields; Simulation; Simulation models; Skewed distributions; Solar activity; Solar wind; Upper atmosphere
• ISSN: 2169-9380; 2169-9402
• DOI: 10.1029/2023JA032320

Ion escape has played a key role in atmospheric loss on ancient Mars due to intense solar activity. Under the existence of a strong global intrinsic magnetic field, as expected on ancient Mars, differential flows between different ion species can be important for ion escape. To assess effects of differential flows, we here developed a new global multifluid magnetohydrodynamics model with a cubed sphere grid named Multifluid Atmospheric Escape Simulations Toward Real elucidatiOn (MAESTRO). A test simulation under present‐day Mars conditions showed solar wind‐Mars interactions, for example, plasma boundaries, ionospheric profiles, and tailward outflows, consistent with observations and simulation studies. We then conducted multifluid and multispecies simulations with six different dipole field strengths under ancient Mars conditions. The multifluid cases show asymmetric outflow distributions with respect to the solar wind convection electric field, as pointed out by previous studies on present‐day Mars. Compared with multispecies cases, the multifluid representation increases the escape rates of O2+ and CO2+ by more than two orders of magnitude in the strong dipole field cases where the cusp outflow is dominant. The O+ escape rate is slightly lower in the multifluid cases with no or weak dipole field due to suppression of ion pickup in the −E hemisphere, while it is reduced by one order of magnitude in the strongest dipole field case. The existence of a dipole field can reduce the total escape rate by a factor of six. The impact on atmospheric evolution is diminished but still significant. Plain Language Summary Mars lost a significant part of the atmosphere during its early period and experienced a drastic climate change. The escape of charged atmospheric particles to space, called ion escape, is a significant removal process of the atmosphere because the activity of the young Sun was much stronger and stripped out the upper atmosphere of early Mars more powerfully. However, it is thought that Mars once had an intrinsic magnetic field like Earth, which can affect the escape of charged particles via electromagnetic forces. To reproduce the realistic processes and morphology of ion escape under the presence of a planetary intrinsic magnetic field, we developed a new simulation model that treats each ion species as a separate fluid. The simulation results of the new model show much stronger molecular ion outflow from the ionosphere at relatively low altitudes