Though no negative ion sensor has flown outside of the Earth, a range of measurements have been done using electron data sets. Such observations have taught and will teach us a lot about space-planet interactions, aeronomy, atmospheric chemistry, and surface evolution. This team will make data analyses of electron, energetic neutral atom, and radar data sets, informed by model simulations and the experience from recent observations, to constrain negative ion populations at different objects in the Solar System. With this team, we will address three science questions linked to three distinct types of planetary negative ion distributions:

1) What is the release and escape rate of volatiles from the Moon?
2) What is the role of meteoric dust and negative ion cluster formation for the atmospheric chemistry at Mars?
3) What is the extent of overlap between solar wind plasma and neutral atmospheres/exospheres of Mars and Comet 67P/Churyumov-Gerasimenko?

Each of these questions will be addressed by specifically targeting the negative ions aspect. These findings will strongly complement previous positive ion and neutral observations. The team is balanced between data analysts, modelers and topic experts from >6 nations and >12 institutions. We plan to meet at ISSI Bern at two occasions, separated by about 12 months. The meetings are required to share data analysis and modelling capacities, efforts and experiences, and share knowledge on new results and reviews. These findings of common interest range from new knowledge on significant planetary negative ion distributions to negative ion observation methods and cross sections for negative ion formation and destruction.