Negative potentials above the day-side lunar surface in the terrestrial plasma sheet: Evidence of non-monotonic potentials

Authors

  • Andrew Poppe,

    1. Laboratory for Atmospheric and Space Physics, Department of Physics, University of Colorado at Boulder, Boulder, Colorado, USA
    2. Colorado Center for Lunar Dust and Atmospheric Studies, University of Colorado at Boulder, Boulder, Colorado, USA
    3. NASA Lunar Science Institute, NASA Ames Research Center, Moffett Field, California, USA
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  • Jasper S. Halekas,

    1. NASA Lunar Science Institute, NASA Ames Research Center, Moffett Field, California, USA
    2. Space Sciences Laboratory, University of California, Berkeley, California, USA
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  • Mihály Horányi

    1. Laboratory for Atmospheric and Space Physics, Department of Physics, University of Colorado at Boulder, Boulder, Colorado, USA
    2. Colorado Center for Lunar Dust and Atmospheric Studies, University of Colorado at Boulder, Boulder, Colorado, USA
    3. NASA Lunar Science Institute, NASA Ames Research Center, Moffett Field, California, USA
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Abstract

[1] The Lunar Prospector (LP) Electron Reflectometer (ER) instrument conducted a series of measurements of the lunar surface potential in a variety of conditions. Occasionally, when the Moon was exposed to the terrestrial plasma sheet and in daylight, large, unexpected negative potentials (∼−500 V) were measured. In this paper, we compare LP ER measurements with one-dimensional particle-in-cell simulations of the potential above the lunar surface when the Moon is exposed to both solar UV radiation and the terrestrial plasma sheet. The simulations show that large negative potentials will be measured by LP ER due to the presence of stable, non-monotonic potentials. Implications of these measurements to other airless bodies in the solar system are also discussed.

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