The SCM instrument for the ESA Plasma Observatory mission

The proposal of the Plasma Observatory mission was selected for a competitive phase A with two other missions in the framework of the seventh call for medium mission (M7) organized by ESA. The mission selection is planned in 2026 for a launch in 2037. Its main objectives are to unveil how are particles energized in space plasma and which processes dominate energy transport and drive coupling between the different regions of the terrestrial magnetospheric system? After the Mission Consolidation Review by ESA in February 2025 followed by reformulation discussions, the mission now consists of seven identical small satellites (Sister spacecraft, SSC) equipped by an updated payload, still evolving along an equatorial elliptical orbit with an apogee ~17 and a perigee ~8 Earth radii. The seven satellites will fly forming two tetraedra and allowing simultaneous measurements at both fluid and ion scales. The mission will include three key science regions: dayside (solar wind, bow shock, magnetosheath, magnetopause), nightside transition region (quasidipolar region, transient near-Earth current sheet, field-aligned currents, braking flow region) and the medium magnetotail. Plasma Observatory mission is the next logical step after the four satellite magnetospheric missions Cluster and MMS. The search-coil magnetometer (SCM), strongly inherited of the SCM designed for the ESA JUICE mission, is now required on the seven SSC. SCM will be delivered by LPP and LPC2E and will provide the three components of the magnetic field fluctuations in the [1Hz-8kHz] frequency range, after digitization by the wave analyser board (WAB) within the electric and magnetic electronics box (BOX-W), relevant for the three key science regions. Continuous waveforms and snapshots every 4 s, will be sampled at 512 Hz and 16 kHz respectively. SCM is planned to be mounted on a 1.5-2 m boom and will have the following sensitivity performances [10^-3, 1.5x10^-6, 5x10^-9, 10^-10, 5x10^-10] nT²/Hz at [1, 10, 100, 1000, 8000] Hz. Associated with the electric field instrument (EFI) of the WAVES instrument suite, SCM will allow to fully characterize the wave polarization and estimate the direction of propagation of the wave energy. These measurements are crucial to understand the role of electromagnetic waves in the energy conversion and partitioning processes, the plasma and energy transport, the acceleration and the heating of the plasma.