Years back, planetary scientists discovered that the Moon, long thought to have no atmosphere, actually has an extremely thin exosphere. But, they have been uncertain about how it gets the layer.
In fact, they believed that the ions that make up the lunar exosphere are generated at Moon’s surface by interaction with solar photons, plasma in the Earth’s magnetosphere, or micrometeorites.
Now, using instruments aboard Japanese lunar orbiter SELENE, an international team made the first spacecraft-based observations of the lunar exosphere when the Moon was inside Earth’s magnetosphere.
The astronomers detected ions of several elements at 100-km altitude above the lunar surface.
Previous studies have detected Moon-originating ions when the Moon was in the solar wind; this new study is the first to detect such ions when the Moon was not affected by solar wind particles or the Earth’s magnetotail plasma.
The results, which provide new evidence about the origin of the lunar exosphere, are consistent with the idea that solar photon-driven processes dominate in supplying exosphere components, the astronomers say.