The investigation of crustal magnetic field signatures at Mars
by the Mars Express ASPERA-3 Electron Spectrometer (ELS).
Doctoral thesis, UCL (University College London).
Mars is a planet that has lacked a global magnetic field for most of its history, around 3.5 billion years, leaving the upper atmosphere unprotected from the scavenging by the solar wind. This is thought to have played a significant role in the evolution of the Martian atmosphere and consequently on the loss of water which once flowed over the surface and made possible the conditions for life to exist. This is unlike the Earth that has a large enough magnetic field to offer protection from the solar wind and radiation. As such, it is important to understand the nature of the space plasma around Mars. In 1998, Mars Global Surveyor discovered magnetisations from the crust of Mars, which altered the view of how the solar wind behaves as it travels past the planet. The importance of these remanent magnetic fields over time and in the different plasma regions around Mars is not completely resolved. This thesis contributes to the understanding of the interaction of Mars with the solar wind and presents the analysis of data from the Analyser of Space Plasmas and Energetic Atoms (ASPERA-3) Electron Spectrometer (ELS) on the Mars Express (MEX) spacecraft, for the investigation of how remanent fields from Mars affect the local space plasma. We have found that the crustal magnetisations have a considerable influence up to the altitudes of 1300 km and possibly enhance the escape of atmosphere beyond. The signature of the crustal fields focusing electrons, called intensifications, occurred with the greatest rates on the dayside below 500 km, due to the intrusion of the solar wind plasma along the crustal fields and from the forcing of the ionopause below its average position. Effects of the crustal fields are most identifiable in the dusk sector and possibly connect regions of large plasma density at higher altitudes (»2000 km) with the atmosphere at low altitudes, and to the magnetic pile-up region, where reconnection with draped IMF could occur. This would allow transport of electrons and ambi-polar extraction of ions over a large distance in altitude and so enhance the escape of the atmosphere. Observations in the regions at night show closed magnetic fields from the crust coincide with voids in the electron flux, a sign of the crustal fields protecting the neutral atmosphere. There was little evidence to connect the distribution of the voids to a Venus-type plasma channel, which limits the amount of atmospheric loss that could occur through ionospheric holes. The voids dominate events on the night side below 500 km, where the rate of intensifications is low. The reverse is true for regions on the nightside above 500 km, where the greatest proportion of intensifications is from the crustal fields, which could occur through aurora and perhaps even tail reconnection.
|Title:||The investigation of crustal magnetic field signatures at Mars by the Mars Express ASPERA-3 Electron Spectrometer (ELS)|
|Additional information:||Authorisation for digitisation not received|
|UCL classification:||UCL > School of BEAMS > Faculty of Maths and Physical Sciences > Space and Climate Physics|
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