Solar control of radar wave absorption by the Martian ionosphere

D. D. Morgan, D. A. Gurnett, D. L. Kirchner, R. L. Huff, D. A. Brain, W. V. Boynton, M. H. Acuña, J. J. Plaut, G. Picardi

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


The MARSIS active sounder aboard the Mars Express spacecraft, under certain conditions in the Martian ionosphere, fails to detect the planetary surface. We have generated a statistical measure of the surface reflection visibility, which we plot as a time series and compare with both in situ particle data taken at Mars and solar x-ray data taken at Earth. We show that loss of the surface signal is closely related to the influx of solar protons at tens of MeV energies. We infer that the influx of high energy solar protons causes impact ionization, increasing the electron density in the Martian ionosphere. At altitudes close to or below 100 km, where the electron-neutral collision frequency is high and the electron density typically has a local maximum, the increased electron density raises the damping coefficient to levels sufficient for complete absorption of the sounding wave over an altitude ranee of a few tens of kilometers.

Original languageEnglish (US)
Article numberL13202
JournalGeophysical Research Letters
Issue number13
StatePublished - Jul 2006

ASJC Scopus subject areas

  • Geophysics
  • General Earth and Planetary Sciences


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