# Chang’E-6 reveals solar wind–dependent H− ions on the Moon

## TL;DR

The Chang’E-6 mission detected negative hydrogen ions on the Moon, revealing their connection to solar wind interactions and improving understanding of lunar plasma environments.

## Contribution

First detection of solar wind-derived negative ions on the Moon using the NILS instrument, revealing their generation and distribution.

## Key findings

- H− spectra correlate positively with solar wind parameters, indicating solar wind–surface interactions generate negative ions.
- Monte Carlo simulations predict a thin dayside H− layer and a long nightside H− tail on the Moon.
- These findings enhance understanding of negative ion generation on airless bodies like the Moon.

## Abstract

Apart from positive ions and electrons, negative ions are expected in various astrophysical environments. However, they have never been detected on the Moon until the Chang’E-6 mission. The NILS instrument onboard Chang’E-6 lander is the first dedicated instrument for detecting negative ions beyond Earth and has successfully obtained H− spectra on the lunar surface, providing an unprecedented opportunity to investigate their origin and distribution. Here, we present a positive correlation between the H− spectra and solar wind parameters, which provides direct evidence for the generation of negative ions from solar wind–surface interaction. Combined with Monte Carlo simulations, we predict a thin dayside H− layer and a long nightside H− tail, which can contribute to the lunar plasma environment, especially during an extreme solar wind density event. These findings greatly improve our understanding of the generation and distribution of negative ions on the Moon and other airless bodies.

Solar wind–derived negative ions have been confirmed on the Moon, which open a window for space plasma and planetary science.