Mars : plasma environment and surface

This doctoral thesis treats parts of the solar wind interaction with the Martian atmosphere and the water-related features known as gullies. The composition of the escaping plasma at Mars has been investigated in an analysis of data from the IMA sensor, which is a part of the ASPERA-3 instrument suit onboard the European satellite Mars Express. The goal of the investigation is to determine if there are any high abundances of escaping ion species incorporating carbon, such as in CO_2^+ . The most abundant ion species was found to be O^+ and O_2^+, followed by CO_2^+. The following ratios were identifed: CO_2^+/O^+ = 0:2 and O_2^+ /O^+ = 0:9. The escaping plasma, in form of ion beam events, has also been correlated to the magnetic anomalies found on the surface, where no clear association was found. Similar ion beams have also been detected on Venus, which does not have any crustal magnetic fields, and hence the fields are not required for the formation process of the beams. The ion beams' dependence of the direction of the solar wind convection electric field has also been studied, where a correlation was found, suggesting that the ion beams are accelerated by this field. The studies mentioned above are important in order to understand the evolution of Mars and its atmosphere, as well as plasma acceleration processes at non-magnetized planetary bodies. On 5 December 2006 the ASPERA instruments of both Venus Express and Mars Express detected a large enhancement in their respective background count level. These readings are associated with events of SEPs (Solar Energetic Particles), which are believed to be coupled with the CMEs (Coronal Mass Ejection) identified 43 ¡ 67 hours after the SEPs. The CMEs occurred on the far side of the sun (with respect to the locations of Venus and Mars), which indicates that these events can a®ect the space weather in areas situated 90 degrees in both azimuthal directions in the heliosphere with respect to the target. During this event the heavy ion outflow from the atmosphere of Mars increased by one order of magnitude, suggesting that EUV flux levels significantly affect the atmospheric loss from unmagnetized bodies. The gully formations have been investigated with data from the MOC, MOLA and TES instruments onboard the satellite Mars Global Surveyor. The features suggest that there has been fluvial erosion on the surface of Mars. The shallow and deep aquifer models remain the most plausible formation theories. Gully formation processes are important to understand since their eroding agent may be liquid water.<p>Godkänd; 2008; 20080206 (ysko)