1,2,3,3,1,2,7,9,11,- 1IRAP/CNRS, Toulouse, France (mathias.rojo@irap.omp.eu)
- 2LPP, Ecole polytechnique, Sorbonne Université, CNRS, Université Paris-Saclay, Observatoire de Paris , Paris-Saclay, France
- 3Department of Climate and Space Sciences and Engineering, University of Michigan,, Ann Arbor, MI, USA
- 4LATMOS/CNRS, Sorbonne University, Paris, France
- 5Department of Geophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
- 6Institute for Space and Earth Environmental Research , University of Nagoya, Nagoya, Japan
- 7Institut für Weltraumforschung, Graz, Austria
- 8Swedish Institute of Space Physics, Solar System Physics and Space Technology, Kiruna, Sweden
- 9Istituto Nazionale di Astrofisica,, Roma, Italy
- 10Institut Supérieur de l'Aéronautique et de l'Espace, Université de Toulouse, Toulouse, France
- 11Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara, Japan
The northern polar cap region of Mercury remains poorly explored, as the MESSENGER orbits were close to the surface. Moreover, this region appears to be
populated by tenuous plasma. The northern polar cap of Mercury was crossed twice during the 4th and 6th flybys of BepiColombo. The Mercury Electron Ana-
lyzer onboard BepiColombo allowed the probing of low-energy electrons for the first time in this region since the third flyby of Mariner 10. We show that the
northern polar cap is populated with dense and cold electrons. Simultaneously, the four ion sensors did not detect any particles. This lack of detection suggests the presence of very cold ions of exospheric origin. Such a measurement challenges current models of Mercury’s exosphere and could be compatible with a closure of Region 1 field aligned currents above the surface.
How to cite: Rojo, M., Dandouras, I., Aizawa, S., Dewey, R., Raines, J., Liu, Z.-Y., Le Liboux, T., Coustillet, C., Gonnet, A., Hadid, L., Harada, Y., Varsani, A., Williamson, H., Millilo, A., André, N., Saito, Y., and Murakami, G.: Evidence of a cold and dense plasma in the northern polar cap of Mercury, Europlanet Science Congress 2026, The Hague, The Netherlands, 7–11 Sep 2026, EPSC2026-896, https://doi.org/10.5194/epsc2026-896, 2026.
