I mentioned above that the Moon has no dense atmosphere. It is known, however, that there is a lunar atmosphere, though it is very tenuous, which contains alkaline materials such as sodium and potassium. This fact was discovered by optical observation from the ground in the 1980s. Another significant achievement by MAP-PACE is the mass analysis of the ions originated in the thin lunar atmosphere or its surface, which was performed from lunar orbit for the first time. Fig. 3 shows the mass distribution of ions. Alkali ions including sodium and potassium were detected. In addition, we confirmed the presence of oxygen, carbon and helium ions. It is possible that ions originating on the lunar surface may contain substances that are sputtered from the surface by the solar wind. By investigating the relation between species of ions and places of origin, we may conduct remote exploration of lunar surface material.
We guess that the findings above are not peculiar to the Moon but common to environments of other celestial bodies that lack strong intrinsic magnetic fields and dense atmospheres. Therefore, by applying the research results on solar wind reflection/scattering on the lunar surface and the release of surface material sputtered by solar wind, we may be able to perform remote surface exploration of objects not yet visited.
In the near future, we plan to send a BepiColombo/MMO (Mercury Magnetospheric Orbiter) to Mercury, the nearest planet to the Sun in the solar system. It is known that Mercury has an intrinsic magnetic field and magnetosphere surrounding it just like the earth. Since Mercury’s magnetic field is weaker than that of the earth, however, there is a possibility that solar wind collides directly with its surface, depending on the solar wind’s situation. As Mercury has no dense atmosphere, unlike the earth, it is thought that its surface environment is similar to the Moon. In future magnetospheric exploration of Mercury, knowledge on the Moon’s plasma environment obtained from KAGUYA’s observations may be of great use to understand the plasma environment around Mercury.
I never thought that the plasma environment around the Moon was so active and interesting until I actually saw the data from KAGUYA. Based on our initial steps with KAGUYA’s observation of plasma around the Moon, our research on plasma environments continues.
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