Observations of a Mini‐Magnetosphere Above the Martian Crustal Magnetic Fields.

Mars is typically regarded as a non‐magnetic planet. Currents in the Martian ionosphere generate a Venus‐like induced magnetosphere which deflects the solar wind flows and piles up the interplanetary magnetic fields. However, crustal magnetic fields in the southern hemisphere influence local plasma properties. Using observations from the MAVEN mission, we characterize the distinguishing plasma characteristics of a mini‐magnetosphere that forms on the Martian dayside. We establish three criteria to differentiate this mini‐magnetosphere from the induced magnetosphere. Notably, the mini‐magnetosphere exhibits higher plasma beta (values near 1), with a balance between planetary ions, crustal magnetic fields, and the solar wind at the magnetopause. Observations show that the crustal magnetosphere reaches an altitude of 1,300 km, larger than one‐third of the Martian radius, indicating a dichotomy between the induced northern and the crustal southern magnetospheres. These findings offer novel insights into the distinctive properties of hybrid magnetospheres in the near‐Mars space. Plain Language Summary: Mars lacks a global intrinsic magnetic field. Currents in the Martian ionosphere generate a Venus‐like induced magnetosphere which deflects the solar wind flow and piles up the interplanetary magnetic field. However, local crustal magnetic fields in Mars' southern hemisphere significantly influence the nearby plasma. With the support of the MAVEN mission, this work analyses observations from passes of the spacecraft through the mini‐magnetosphere during suitable orbits and investigates plasma pressures in both single orbit data and by a 4‐year statistical analysis. We present an observation of a mini‐magnetosphere filled by trapped heavy ions above the crustal magnetic fields on the Martian dayside. Furthermore, we establish three criteria to distinguish this mini‐magnetosphere from the induced magnetosphere. Observations show that the mini‐magnetosphere reaches an altitude of 1,300 km, larger than one‐third of the Martian radius. The observed mini‐magnetosphere and the dichotomy between the crustal southern and induced northern Martian magnetosphere forms a distinct environment that may help us to test the interactions between stellar winds and magnetic or nonmagnetic bodies. Key Points: The crustal magnetic fields trap ionospheric plasma to form a mini‐magnetosphere in the near‐Mars plasma environmentThe mini‐magnetosphere reaches 1,300 km on the Martian daysideThe mini‐magnetosphere balances the solar wind through contributions from plasma thermal pressure and the crustal magnetic pressure [ABSTRACT FROM AUTHOR]