Observations of Ionospheric Oxygen in the Vicinity of the Moon

Using data from the ARTEMIS spacecraft, we report on observations consistent with the detection of ionospheric oxygen ions in the terrestrial magnetosphere at lunar altitudes. Since there is no mass spectrometer onboard the spacecraft, oxygen can only be detected when the outflow velocities are sufficient to separate oxygen from hydrogen in energy (for the same velocity, oxygen will appear to have a higher energy). We catalog the occurrence of such signatures and relate the detection, number density, and energy of ionospheric oxygen ions to geomagnetic activity parameters. These observations shed light on the amount of ionospheric plasma that reaches the Moon in the magnetotail and how this plasma may participate in and contribute to magnetospheric activity and lunar exosphere production