Similarly, the low-latitude ionosphere can be imaged from the Moon by detecting the UV emissions of ionospheric ions. Emissions from O+ ions have been used to track the formation and evolution of density troughs associated with the ionospheric spread-F phenomena. The motions of the density troughs, as shown in Figure 6.4, can be used to measure the evolution of large-scale ionospheric electric fields.

Energetic neutral atom imaging was shown to be effective during the IMAGE mission over a very large energy range, from 10 eV to 500 keV. One of the most important imaging targets is the ring current, which builds up in timescales of hours during magnetic storms and is a key ingredient in the dynamics of Earth’s magnetosphere. An example of a ring current image taken from a low-latitude perspective is shown in Figure 6.5.

In summary, imaging from the Moon will provide a new perspective on magnetospheric and ionospheric dynamics because of the possibility of making observations from a vantage point providing a global view and for time spans substantially longer than the timescales of interest for these very dynamic phenomena.

The instrumentation for lunar-based geospace imaging would be based on the flight-proven IMAGE instruments with correspondingly larger apertures to allow for the approximately seven times larger distance. Multispectral UV and ENA imagers would require relatively modest resources, in the range of 50 kg to 100 kg and 30 W to 50 W each. Deployment could be done either robotically or by astronauts.

Finding 5: The Moon may provide a unique location for observation and study of Earth, near-Earth space, and the universe.

The Moon is a platform that can potentially be used to make observations of Earth (Earth science) and to collect data for heliophysics, astrophysics, and astrobiology. Locations on the Moon provide both advantages and disadvantages. There are substantial uncertainties in the benefits and the costs of using the Moon as an observation platform as compared with alternate locations in space. The present committee did not have the required span

FIGURE 6.4 Oxygen airglow images for (a) May 1, 2002, and (b) May 3, 2002, showing nightside equatorial plasma bubbles whose drift motion can be used to determine ionospheric electric fields. (The arrows identify “bubbles” in the ionosphere, which are used to determine ambient plasma drift speeds in the second part of the figure, not shown here.) Data from Imager for Magnetopause-to-Aurora Global Exploration (IMAGE)-far-ultraviolet instrument. SOURCE: Courtesy of T.J. Immel, H.U. Frey, S.B. Mende, and E. Sagawa, Global observations of the zonal drift speed of equatorial ionospheric plasma bubbles, Ann. Geophys. 22:3099-3107, 2004.

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