The Jovian Ion and Electron spectrometer, part of the PEP instrument suite, used the opportunity to make a very rare observation of the molecular ion fraction of the plasmasphere’s plasma. The passage offered an uncommon chance to characterize the molecular ion fraction of the plasmasphere's cold and dense plasma.

The analysis also demonstrated a technical capability of the instrument: it can resolve ion masses by using the negative electrical potential of the spacecraft itself. This effect helps separate ions of different mass as they reach the detector, allowing the spectrometer to distinguish species that would otherwise be difficult to tell apart.

The observations were made with the PEP JEI and RPWI instruments on the JUICE spacecraft.

The results are reported in Annales Geophysicae, with the work led by Markus Fränz and an international team of co-authors.

Subject of Research: Ion composition of the Earth plasmasphere observed by instruments on the JUICE spacecraft during its first Earth gravity assist

Article Title: Ion composition of the Earth plasmasphere observed by the PEP JEI and RPWI instruments on the JUICE spacecraft

Article References: Fränz, M., Fischer, H., Krupp, N., Roussos, E., Wittmann, P., Bambach, P., Wahlund, J.-E., Stenberg Wieser, G., Barabash, S., Holmberg, M., Zeroual, M., Brandt, P. C., Wurz, P., Wieser, M., Futaana, Y., Shimoyama, M., Pontoni, A., Vorburger, A., Galli, A., … Baláž, J. (2026). Ion composition of the Earth plasmasphere observed by the PEP JEI and RPWI instruments on the JUICE spacecraft. Annales Geophysicae, 44(2), 1143-1165. https://doi.org/10.5194/angeo-44-1143-2026

Image Credits: AI Generated

DOI: 10.5194/angeo-44-1143-2026

Keywords: JUICE, Earth plasmasphere, ion composition, molecular ions, PEP JEI, RPWI, gravity assist, space plasma, ion spectrometer, spacecraft potential, composition, Earth