Volume 128, Issue 2 e2022JA031027
Research Article

Electron Densities and Temperatures in the Martian Ionosphere: MAVEN LPW Observations of Control by Crustal Fields

David J. Andrews

Corresponding Author

David J. Andrews

Swedish Institute of Space Physics, Uppsala, Sweden

Correspondence to:

D. J. Andrews,

[email protected]

Contribution: Conceptualization, Methodology, Software, Validation, Formal analysis, ​Investigation, Resources, Writing - original draft, Writing - review & editing, Visualization, Supervision, Project administration, Funding acquisition

Search for more papers by this author
Katerina Stergiopoulou

Katerina Stergiopoulou

Swedish Institute of Space Physics, Uppsala, Sweden

School of Physics and Astronomy, University of Leicester, Leicester, UK

Contribution: Methodology, Software, Validation, Formal analysis, ​Investigation, Writing - original draft, Writing - review & editing, Visualization

Search for more papers by this author
Laila Andersson

Laila Andersson

Laboratory for Atmospheric and Space Plasmas, University of Colorado, Boulder, CO, USA

Contribution: Methodology, Software, Validation, Data curation, Writing - review & editing

Search for more papers by this author
Anders I. E. Eriksson

Anders I. E. Eriksson

Swedish Institute of Space Physics, Uppsala, Sweden

Contribution: Methodology, Writing - review & editing, Supervision

Search for more papers by this author
Robert E. Ergun

Robert E. Ergun

Laboratory for Atmospheric and Space Plasmas, University of Colorado, Boulder, CO, USA

Contribution: Methodology, Software, Validation, Data curation

Search for more papers by this author
Marcin Pilinski

Marcin Pilinski

Laboratory for Atmospheric and Space Plasmas, University of Colorado, Boulder, CO, USA

Contribution: Software, Data curation

Search for more papers by this author
First published: 08 February 2023
Citations: 3
The copyright line for this article was changed on 9 MAR 2023 after original online publication.

Abstract

Mars Express and Mars Atmosphere and Volatile Evolution (MAVEN) observations have demonstrated the influence of Mars's spatially variable crustal magnetic fields upon the configuration of the plasma in the ionosphere. This influence furthermore leads to variations in ionospheric escape, conceivably in part through the modification of the plasma density and electron temperature in the upper ionosphere. In this study, we examine MAVEN Langmuir Probe and Waves data, finding a clear correspondence between the structure of the crustal fields and both the measured electron temperatures and densities, by first constructing an “average” profile from which departures can be quantified. Electron temperatures are shown to be lower in regions of strong crustal fields over a wide altitude range. We extend previous analyses to cover the nightside ionosphere, finding the same effects present to a lesser degree, in contrast to previous studies where the opposite relationship was found between densities and crustal fields. We further determine the altitude range over which this coupling between both plasma density (and temperature) and crustal fields is effective and use measurements made by MAVEN in the solar wind to explore the dependence of this crustal field control on the coupling to the solar wind and the interplanetary magnetic field (IMF). Based on this, there is some suggestion that variations in the solar wind dynamic pressure are associated with modulation of the effects of the crustal fields on plasma density, whereas the strength of the IMF modulates the crustal fields effects on both electron densities and temperatures.

Key Points

  • We present a statistical analysis of Mars Atmosphere and Volatile Evolution Langmuir Probe and Wave densities and temperatures at Mars

  • Densities are elevated and temperatures reduced in strong crustal field regions, on both the dayside and nightside

  • Variations in the driving solar wind conditions are able to affect these correlations to a modest degree

Plain Language Summary

Mars's atmosphere is exposed to ultra-violet light from the Sun, forming a layer of plasma at high altitudes around the planet. This plasma layer, termed the ionosphere, is strongly affected in terms of its density and temperature, both by external factors like the solar wind and the interplanetary magnetic field (IMF), and internal factors, like Mars's crustal magnetic field. Here, we study how effective the crustal magnetic fields are at shaping the ionosphere in both density and temperature, by first determining the average structure of the ionosphere, and then examining departures from this average. We find that plasma densities are elevated and temperatures reduced in regions where the crustal field is stronger. We also find the same effect on the nightside. This result is in apparent opposition to previous related studies, now based on a much larger data set, which we suggest may be the result of poor seasonal sampling in earlier studies. We further investigate how this crustal field control varies with the solar wind and IMF, and see evidence for weak modulation according to both the dynamic pressure exerted by the solar wind, and the strength of the IMF.

Data Availability Statement

MAVEN LPW data used in this study are available from the NASA Planetary Plasma Interactions Node, https://pds-ppi.igpp.ucla.edu/search/view/?id=pds://PPI/maven.lpw.derived, as are MAG and SWIA data products, https://pds-ppi.igpp.ucla.edu/search/view/?id=pds://PPI/maven.mag.calibrated, and https://pds-ppi.igpp.ucla.edu/search/view/?id=pds://PPI/maven.swia.calibrated. The authors thank the MAVEN Science Data Center team for provision of code in particular the cdflib python package.