R. Piberne

The Spatio‐Temporal Analysis of Field Fluctuations (STAFF) instruments onboard the Cluster satellites were designed to measure magnetic fluctuations in the 0.2–12 Hz and 0.2–180 Hz frequency ranges from the Search‐Coil Magnetometer (SCM), as well as electromagnetic spectra from the Spectrum Analyzer (SA) in the 8–4,000 Hz range. They provided a considerable amount of data throughout the 24‐year mission. The production and calibration of these data sets were detailed in Robert et al. (2014, https://doi.org/10.5194/gi‐3‐153‐2014 ), which demonstrated its excellent quality and good agreement with the fluxgate magnetometer (FGM) measurements over their common frequency range. The Cluster's 24 years of operation, which far exceed the nominal 2‐year mission, represent the longest flight of search coil magnetometers and offer a unique opportunity to evaluate their performance over such a long period, as well as to compare the results of four initially identical instruments. The present work, based on data now archived at the Cluster Scientific Archive (CSA), examines the evolution of these products after the first 11 years in space, and until the end of the Cluster operations in September 2024. The quality of the measurements, calibration, sensitivities, and their agreement between spacecraft proved to be excellent and remained stable throughout the mission. Comparison of spectra derived from the calibrated waveforms of STAFF (CWF) and FGM shows a very good agreement until the end of operations, a further proof of the high quality of their respective calibrations.

In this study, we combine Cassini fields and particle observations to investigate Titan's induced magnetosphere from the TA to T82 flybys, including flybys from the Cassini prime, equinox, and part of the solstice mission, to investigate the average location and the shape of Titan's induced magnetosphere. Although earlier studies have provided valuable information on Titan's induced magnetosphere, they were largely based on separate analyses of fields and particle data. We provide an integrated map of electron density and temperature in Titan's near plasma environment to outline the external boundary of the induced magnetosphere. We identify a dense ionospheric region and an extended plasma wake with electron densities ranging between and c. In addition, we systematize the spatial distribution of pick‐up ions at Titan with respect to the background convective electric field. We indicate that pickup ions are found in the positive hemisphere of the Kronian plasma convective electric field. The mass of the observed pickup corresponds to methane group ions, ions as well as protons and molecular hydrogen ions. The Kronian background electric field progressively accelerates these ions, and we estimate its intensity by reconstructing the radial energy gain of this population in response to the convective electric field. We find the estimated from the pickup ions electric field values within 0.05 mV and 1.92 mV range, which is consistent with an estimate of 0.61 mV deduced from computation.

Cassini plasma wave and charged particle observations are combined with magnetometer measurements to investigate Titan’s induced magnetosphere. Electric field emissions close to Titan are identified as upper hybrid resonance emissions, which provide a density estimate of Titan’s cold plasma. These observations have been combined with electron spectrometer measurements to build an integrated map of electron density in Titan’s near environment using observations from TA to T82 flybys, ie which includes flybys from the Cassini prime, equinox and part of the soltice mission. We identify a dense ionospheric region and an extended plasma wake with values ranging between 10 ^-2 and 10 ³ cm ^-3 . Upstream of the induced magnetosphere, the presence of pickup ions in the positive hemisphere of the kronian plasma convective electric field are detected. The mass of the observed pickup corresponds to methane group ions, N ₂ ⁺ and HCNH ⁺ ions as well as Titan’s protons and molecular hydrogen ions. These ions are progressively accelerated by the kronian background electric field and we estimate its intensity by reconstructing the energization of this population. We find values on the order of 0.7 mV/m , consistent with an average estimate of 0.61 mV/m deduced from ∼ |VxB| computation.