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Ionosphere on the moon?• Given the removal of ionized species by the solar wind and

the very low ionization rate in the thin neutral atmosphere, the density of the lunar ionosphere is expected to be ~1 cm-3.

• Soviet Luna 19 and 22 in 1970s detected electron layers near the lunar surface with densities of several hundreds of cm-3

and thicknesses of several tens of kilometers. • The reliability of the measurements is still under debate.

Schematic of radio occultation:Column electron density integrated along the ray path is measured.

<VaVWV&!"#$%&<'$.+'.• To clarify whether lunar ionosphere (electron layer)

exists or not• (If it exists) To study the origin of the ionosphere by

comparing results under different conditions

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UA OVW0X6

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Temperature

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Distance

Velocity

0 km/s10 Rs 20 RsSurface

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Distance10 Rs 20 RsSurface

Earth orbit Akatsuki’s trajectory before arrival at Venus

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