DATE2026.02.27 #Press Releases

Discovered daily variations of ions in a thin lunar atmosphere

-KAGUYA Reveals the Mechanism of CNO Ion Formation

Summary

A research group led by Professor Kentaro Terada and Associate Professor Katsuichiro Yokota of the Department of Space and Earth Science and the Center for Mass Spectrometry, Graduate School of Science, Osaka University, and Assistant Professor Shota Notsu of the Department of Earth and Planetary Science, Graduate School of Science, The University of Tokyo has revealed the formation mechanism of CNO ions in the lunar exosphere through detailed analysis of daily variations of ions in a thin lunar atmosphere (ions in the outer atmosphere). They found that the carbon (C), nitrogen (N), and oxygen (O) ions on the day side of the lunar exosphere are mainly produced by the solar wind.

In addition, as a result of analyzing the temporal variation of the C⁺/O⁺ ratio, they discovered for the first time in the world that the lunar atmosphere temporarily changes to a "carbon-rich" state immediately after a meteor shower. Furthermore, by examining the correlation with the N⁺/O⁺ ratio, it became clear that there are two types of components with different origins on the lunar surface: a component with a high nitrogen ratio ( N⁺/C⁺ ratio) and a component of carbon oxide (CO or CO₂ ) origin that does not contain nitrogen.

Diurnal variations of each element have not been adequately captured in the past, since the analysis of time-integrated data has been conducted mainly. This time, the research group established a new analysis method that can discuss the time variations of individual elements in detail by combining the classification of long-term data acquired by the ion mass spectrometer onboard the Japanese lunar explorer "KAGUYA" by day/night and phase, and the peak resolution of mass spectra.

Figure: Ion formation mechanism in the lunar exosphere

Links

Osaka University

Journal article