Making Waves: Mirror Mode Structures Around Mars Observed by the MAVEN Spacecraft

We present an in‐depth analysis of a time interval when quasi‐linear mirror mode structures were detected by magnetic field and plasma measurements as observed by the NASA/Mars Atmosphere and Volatile EvolutioN spacecraft. We employ ion and electron spectrometers in tandem to support the magnetic field measurements and confirm that the signatures are indeed mirror modes. Wedged against the magnetic pile‐up boundary, the low‐frequency signatures last on average ∼10$\sim 10$s with corresponding sizes of the order of 15–30 upstream solar wind proton thermal gyroradii, or 10–20 proton gyroradii in the immediate wake of the quasi‐perpendicular bow shock. Their peak‐to‐peak amplitudes are of the order of 30–35 nT with respect to the background field, and appear as a mixture of dips and peaks, suggesting that they may have been at different stages in their evolution. Situated in a marginally stable plasma with β‖∼ 1, we hypothesize that these so‐called magnetic bottles, containing a relatively higher energy and denser ion population with respect to the background plasma, are formed upstream of the spacecraft behind the quasi‐perpendicular shock. These signatures are very reminiscent of magnetic bottles found at other unmagnetized objects such as Venus and comets, also interpreted as mirror modes. Our case study constitutes the first unmistakable identification and characterization of mirror modes at Mars from the joint points of view of magnetic field, electron and ion measurements. Up until now, the lack of high‐temporal resolution plasma measurements has prevented such an in‐depth study. We detect mirror mode structures at Mars, about 15–30 solar wind thermal proton gyroradii in sizeFor the first time, we use Mars Atmosphere and Volatile EvolutioN magnetic field, ion and electron data to characterize them fullyLocated in the deep magnetosheath, they are likely created behind the quasi‐perpendicular shock We detect mirror mode structures at Mars, about 15–30 solar wind thermal proton gyroradii in size For the first time, we use Mars Atmosphere and Volatile EvolutioN magnetic field, ion and electron data to characterize them fully Located in the deep magnetosheath, they are likely created behind the quasi‐perpendicular shock