Lunar energetic neutral atom (ENA) spectra measured by the interstellar boundary explorer (IBEX)

F. Allegrini, M. A. Dayeh, M. I. Desai, H. O. Funsten, S. A. Fuselier, P. H. Janzen, D. J. McComas, E. Möbius, D. B. Reisenfeld, D. F. Rodríguez M., N. Schwadron, P. Wurz

Research output: Contribution to journalArticlepeer-review

31 Scopus citations


The solar wind continuously flows out from the Sun, filling interplanetary space and directly interacting with the surfaces of small planetary bodies and other objects throughout the solar system. A significant fraction of these ions backscatter from the surface as energetic neutral atoms (ENAs). The first observations of these ENA emissions from the Moon were recently reported from the Interstellar Boundary Explorer (IBEX). These observations yielded a lunar ENA albedo of ∼10% and showed that the Moon reflects ∼150 metric tons of neutral hydrogen per year. More recently, a survey of the first 2.5 years of IBEX observations of lunar ENAs was conducted for times when the Moon was in the solar wind. Here, we present the first IBEX ENA observations when the Moon is inside the terrestrial magnetosheath and compare them with observations when the Moon is in the solar wind. Our analysis shows that: (1) the ENA intensities are on average higher when the Moon is in the magnetosheath, (2) the energy spectra are similar above ~0.6* solar wind energy but below there are large differences of the order of a factor of 10, (3) the energy spectra resemble a power law with a "hump" at ∼0.6* solar wind energy, and (4) this "hump" is broader when the Moon is in the magnetosheath. We explore potential scenarios to explain the differences, namely the effects of the topography of the lunar surface and the consequences of a very different Mach number in the solar wind versus in the magnetosheath.

Original languageEnglish (US)
Pages (from-to)232-242
Number of pages11
JournalPlanetary and Space Science
StatePublished - Sep 1 2013
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • ENA
  • Energetic neutral atoms
  • IBEX
  • Moon albedo
  • Solar wind


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