13:00 - 14:00
Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse / CNRS / CNES, Toulouse, France
Heavy atomic and molecular ions escaping from a planetary atmosphere can contribute to the long-term evolution of its composition. Here we have examined Cluster spacecraft data acquired by the CIS-CODIF ion mass spectrometer, obtained in the terrestrial inner magnetosphere. Analysis shows that the CIS-CODIF instrument detected, in upwelling ion beams and in the ring current, a series of energetic ion species including not only atomic ions as O+ but also molecular ions around ~30 amu. Given the 5-7 m/Δm mass resolution of the instrument, these could include N2+, NO+, or O2+. Their density, when these molecular ions were present, was from a few up to 28% of the O+ density. The events were during active periods, with CME arrivals followed by a northward rotation of the IMF. For four of these events, for which the orbital conditions were favourable, the observations by Cluster preceded the observations of outflowing heavy ions by the ARTEMIS spacecraft, at lunar distances in the terrestrial magnetotail, reported by Poppe et al. . The upwelling O+ fluxes, measured by Cluster in the inner magnetosphere, are consistent with the heavy ion fluxes measured by ARTEMIS. These events constitute the first coordinated heavy ion outflow observation in the Earth’s inner magnetosphere and at the Moon. They show the existence of a direct pathway of plasma, upwelling from the ionosphere and then transported and lost into the deep magnetotail. They show also that molecular ion escape, during active periods, is an additional escape mechanism (with respect to the atomic ion escape). Quantifying these mechanisms is important in order to understand the long-term (billion years scale) evolution of the atmospheric composition, and in particular the evolution of the N/O ratio, which is essential for habitability. Future missions should investigate in detail the mechanisms of atomic and molecular ion acceleration and escape, their link to the solar and magnetospheric activity, and their role in the magnetospheric dynamics and in the long-term evolution of the atmospheric composition. Our observations suggest also that terrestrial heavy ions, transported to the Moon, may have preserved samples of the Earth’s atmosphere of billions of years ago by their implantation in the near side lunar regolith. They thus stimulate exciting directions for in situ lunar science, in assessing the amount of atomic and molecular ion species which could be implanted in the lunar regolith, and preserved through time, despite regolith gardening and reworking processes. They show also the importance of the deep magnetotail of the Earth in monitoring outflowing heavy ions, as proposed in the FATE (Far Tail Explorer) mission.