Venus and Mars in the solar wind. A Comparative study over four solar cycles.

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Planets with an intrinsic magnetic field form so-called magnetospheres (a space around the planet dominated by the planetary magnetic field) which protect their atmospheres/ionospheres from the direct interaction and contact with the magnetized plasma flow of the solar wind. There are planets, like Mars and Venus, which do not posses an intrinsic magnetic field and their atmospheres/ionospheres may have direct contact with the solar wind. The magnetized solar wind, however, creates currents in the ionosphere which induce a magnetic field and an induced magnetosphere is formed much closer to the planet, however, than an intrinsic magnetosphere. Despite a wealth of in-situ and remote sensing data collected by many spacecraft over the past four solar cycles, the physics of induced magnetospheres is still insufficiently explored. This project shall focus on the cases of Venus and Mars in order to get a coherent picture of the formation and characteristics of induced magnetosphere. Observations suggest that the structure of their induced magnetospheres is drastically changed by variations of both the solar EUV radiation and the solar wind. A reevaluation of the observational data obtained during the previous missions to Mars and Venus (Pioneer Venus Orbiter (PVO), Venus Express (VEX), Mars Global Surveyor (MGS)) and an analysis of the data from still operational spacecraft (Mars Express (MEX), Mars Atmosphere and Volatile EvolutioN (MAVEN)) shall be performed. The project shall be jointly performed by a collaboration of the two research groups located at the Rheinisches Institut für Umweltforschung (RIU) in Köln, Germany, and the Institute of Space Research (IKI) in Moscow, Russia. The team at RIU shall focus on the study of Venus and Mars ionospheres by a multi-instrument analysis and correlation of observations performed by the PVO, VEX, MGS, MEX and MAVEN spacecraft. This study shall analyze the unmagnetized and magnetized ionospheric states affected by the external drivers (solar EUV flux and solar wind) onto the ionospheres. The magnitude of these external drivers varies with both heliocentric distance and the solar activity and the ionosphere becomes weaker or stronger which may significantly change the physics of the solar wind/ionosphere interaction. The RIU team in this project shall target the analysis of observational to study the main effects of the solar wind/ionosphere interaction, while the IKI team shall examine the theoretical aspects of the induced magnetospheres including the mechanisms of the magnetic field pile-up and the penetration of the interplanetary magnetic fields into the ionosphere at the dayside, problems of the stability and disruption of the magnetic tail. The results shall have relevance for other planets without magnetic fields like Pluto, comets, large moons with atmospheres and in principle also for exoplanets.