ENAs from the Moon

Because the Moon has no magnetosphere and no atmosphere, it exhibits quite different characteristics of interaction with the solar wind compared with those of the Earth, Mars, and Venus. Energetic neutral atom (ENA) environment is obviously quite different from them, therefore, ENA measurement have new possibilities of contributions to lunar sciences. This presentation reviews ENA generation mechanisms at the Moon, and discusses feasible applications of ENA measurement to lunar sciences. Owing to the lack of the magnetosphere and atmosphere, the solar wind can directly reach the lunar surface, and surface atoms are sputtered to space. The sputtered atoms are thought to conserve the surface composition. This means that we can introduce new technology for investigating the lunar surface composition by measuring lunar ENAs from space. In addition to the sputtered ENAs, solar wind particles reflected at the surface can be measured by ENA instrument (most of the protons are converted to neutral hydrogens during the reflection). They enable us to investigate coupling among penetration, implantation and reflection of the solar wind particles at the lunar surface. One application is that we can use the reflected neutral atom in order to study the correlation between the existence of the magnetic anomalies and characteristic albedo structure.