MAVEN Observations of Tailward Reconnection Front in the Martian Magnetotail.

Intense electromagnetic energy conversion and local magnetic flux transport occur at reconnection fronts (RFs) formed by magnetic reconnection. Tailward RFs (TRFs), characterized by sharply enhanced negative magnetic field normal components accompanied by tailward plasma flows, are the tailward propagating dipolarization fronts in the Earth's magnetotail. So far RFs and TRFs are observed merely at magnetized planets. Using data from Mars Atmosphere and Volatile EvolutioN, we report, for the first time, the observations of TRF embedded in a current sheet (possibly diffusion region of magnetic reconnection) in the Martian magnetotail. At the TRF, O+ and O2+ are accelerated in tailward direction; behind the TRF, the perpendicular electron fluxes enhance at the energy of 251–905 eV, which should be caused by betatron acceleration. The energized plasmas indicate that the electromagnetic energy converts to plasma kinetic energy around the TRF. Our observations suggest that RFs could occur in the planetary magnetotail without the global intrinsic dipole magnetic field. Plain Language Summary: Magnetic reconnection is a process that the anti‐parallel magnetic field lines break and reconnect, accompanied by explosive energy conversion. Without a global dipole magnetic field, Mars has interesting flexible magnetic fields in the magnetotail, which can be varied corresponding to the upstream interplanetary magnetic field. Magnetic reconnection occurs during the interplanetary magnetic field and Martian solar‐wind‐induced magnetosphere. Tailward reconnection fronts, characterized by sharply enhanced negative magnetic field normal components usually accompanied by tailward plasma flows, are generally formed by magnetic reconnection. Intense electromagnetic energy conversion occurs at reconnection fronts, consistent with local magnetic flux transport and global magnetotail flux reduction in the magnetotail. Utilizing measurements from the Mars Atmosphere and Volatile EvolutioN orbiter, for the first time we report the observations of tailward reconnection fronts in the near‐Mars magnetotail, which is unexpected for a planet without an intrinsic dipole magnetic field. Besides, ion acceleration and electron acceleration are found around the tailward reconnection fronts. Our work offers a new perspective and shows the importance of magnetic reconnection on the evolution of the near‐Mars magnetotail. Key Points: A tailward reconnection front is observed in the near‐Mars magnetotail for the first timeHeavy ion acceleration and electron acceleration are detected around the tailward reconnection frontReconnection fronts could occur in the planetary magnetotail without the global intrinsic dipole magnetic field [ABSTRACT FROM AUTHOR]