The Earth's geocorona as viewed from the surface of Moon.
This image was acquired during the Apollo 16 mission
(April 1972) with the Naval Research Laboratory's far-
ultraviolet camera/spectrograph. The Sun is to the left; the
Earth's north pole is toward the upper left. The geocoronal
emissions are due to resonantly scattered solar Lyman alpha
photons (wavelength = 1216 angstrom). The southern aurora
can be seen on the Earth's night side.
Charge exchange reactions between hot ring current ions and exospheric hydrogen produce the energetic neutral atoms that will be detected with IMAGE's neutral atom imagers and used to construct images of the ring current as it evolves in response to changing magnetospheric conditions. IMAGE's FUV geocorona photometers (GEO) will observe geocoronal Lyman alpha emissions and provide data on the exospheric hydrogen densities that will be used in the interpretation of the neutral atom observations.
Source: Carruthers, Page, and Meier, Apollo 16 Lyman alpha
imagery of the hydrogen geocorona, J. Geophys. Res., 81,