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Mars' Ionopause: A Matter of Pressures

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  • B. Sánchez-Cano
  • C. Narvaez
  • M. Lester
  • M. Mendillo
  • M. Mayyasi
  • M. Holmstrom
  • J. Halekas
  • L. Andersson
  • C.M. Fowler
  • J.P. McFadden
  • S. Durward
Article numbere2020JA028145
<mark>Journal publication date</mark>18/09/2020
<mark>Journal</mark>Journal of Geophysical Research: Space Physics
Issue number9
Number of pages19
Publication StatusPublished
<mark>Original language</mark>English


This study assesses under what circumstances the Martian ionopause is formed on the dayside, both in regions where there are strong crustal magnetic fields and areas where these fields are small (<30 nT). Multiple data sets from three MAVEN dayside deep dip campaigns are utilized between periapsis and 600–1,000 km, as well as solar wind observations from Mars Express. The ionopause is identified as a sudden decrease of the electron density with increasing altitude and a simultaneous increase of the electron temperature and variability below 400 km. This is a physically robust approach as the electron temperature is a key parameter in determining the structure of the ionospheric profile, and, therefore, also a strong indicator of the ionopause location. We find that 36% (54%) of the electron density profiles over strong (weak) crustal magnetic field regions had an ionopause event. We also evaluate the roles of ionospheric thermal and magnetic pressures on the ionopause formation as well as the presence of solar wind particles, H+, down to the location of the ionopause. We found that the topside ionosphere is typically magnetized at mostly all altitudes. The ionopause, if formed, occurs where the total ionospheric pressure (magnetic + thermal) equals the upstream solar wind dynamic pressure. Moreover, the lower edge of the ionopause coincides with the altitude where the solar wind flow stops: The thermal pressure suffers a significant reduction with increasing altitude and the solar wind proton density has a prominent increase.