Abstract We present Mars Express (MEX) observations of heavy pickup ions (HPUI) at Mars and a new method to derive interplanetary magnetic field (IMF) properties. The MEX HPUI measurements were organized using the upstream IMF directions measured by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. Since these HPUIs are mostly accelerated by the electric field in the upstream and magnetosheath regions, the IMF component perpendicular to the solar wind, both directions and magnitudes, can be derived from the HPUI flux directions, energies, and positions measured by MEX. The derived IMF properties were compared with the simultaneous IMF measurements by MAVEN, which showed good agreements with each other with the accuracy comparable to most previous IMF proxies based on MAVEN data. This new IMF proxy does not require any magnetic field data and hence can be applied to the long time period prior to the MAVEN mission.

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