Impact of Coronal Mass Ejection-driven Enhanced Magnetic Pressure on the Martian Northern Hemispheric Ionosphere during 2024 May 17–18

The Martian northern hemisphere (NH) is relatively devoid of ambient magnetic fields compared to the southern hemisphere (SH), which houses the strong crustal field regions. On 2024 May 17, when Mars was hit by a coronal mass ejection (CME), the periapsis of NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft was entirely in the NH. The dynamic pressure in the ionosphere was enhanced by almost 2 orders of magnitude during the Mars–CME interaction, allowing penetration of solar origin magnetic fields into the Martian ionosphere. Even at altitudes below 500 km, the ratio of magnetic pressure ( P _b ) to ionospheric thermal pressure ( P _th ) was amplified more than 100 times, creating an overpressure (OP) regime. This OP condition exposed the topside ionosphere to the CME. The topside ionosphere was severely depleted, with the electron ( n _e ) and ${{\rm{O}}}_{2}^{+}$ ( ${n}_{{{\rm{O}}}_{2}^{+}}$ ) densities being reduced by nearly 50%–100%. The effects were particularly severe at altitudes above 350 km. The dayside ionosphere showed relatively stronger depletion compared to the terminator regions.