NASA’s EZIE mission, a Heliophysics Mission of Opportunity (MoO), launched on March 15, 2025 and consists of three 6-U cubesats designed to study the ionospheric electrojets. The electrojets are horizontal ionospheric currents that flow between regions of inward and outward field-aligned currents (FACs) that couple the ionosphere to the dynamic magnetosphere. Although the general characteristics of the electrojets are well-known, there are temporal and spatial aspects that are poorly understood and require new measurements. EZIE is designed to answer these questions and provide a new approach for making the measurements. Each cubesat carries 4 Microwave Electrojet Magnetogram (MEM) instruments, a 118.75 GHz mm-wave polarimetric radiometric system with a digital spectrometer backend. MEM measures the 118-GHz O2 Zeeman split in frequency of the Oxygen absorption line that is directly proportional to the strength of the magnetic field of the observation. In this way, EZIE can infer the magnetic field at ~80-85 km, very near the source of region of the electrojets, a vast improvement over ground-based magnetometers. EZIE is the first mission that uses all polarizations of the Zeeman lines to study electrojet-induced geomagnetic disturbances in the lower ionosphere. It builds on the success of Aura Microwave Limb Sounder (MLS) that measures the horizontal (H) and vertical (V) polarizations of this emission for upper atmospheric sounding since 2004. In this talk, I first provide an introduction to magnetosphere-ionosphere coupling, then review the science objectives and the mission and measurement approach. I then walk through the magnetic field retrieval process, a numerically intensive activity that has been described by the team as a science investigation in and of itself. Finally, I present some of the first results from this exciting mission, demonstrating how EZIE provides a giant leap forward in understanding ionospheric currents.
