The IMF pile-up regions near the Earth and Venus: Lessons for the solar wind - Mars interaction

The Mars Global Surveyor mission has revealed that localized crustal paleom agnetic anomalies are a common feature of the Southern Hemisphere of Mars. The magnetometer measured small-scale magnetic fields associated with many individual magnetic anomalies have magnitudes ranging from hundreds to thou sands nT at altitude above 120 km. That makes Mars globally different from both Venus and Earth. The data collected by Lunar Prospector near the Moon were interpreted as evidence that above regions of inferred strong surface magnetic fields on the Moon the SW flow is deflected, and a small-scale min i-magnetosphere exists under some circumstances. With a factor of 100 stron ger magnetic fields at Mars and a lower SW dynamic pressure, those conditio ns offer the opportunity for a larger size of small `magnetospheres' which can be formed by the crustal magnetic fields. Outside the regions of the ma gnetic anomalies, the SW/Mars interaction is Venus-like. Thus, at Mars the distinguishing feature of the magnetic field pile-up boundary most likely v aries from Venus-like to Earth-like above the crustal magnetic field region s. The observational data regarding the IMF pile-up regions near Venus and the Earth are initially reviewed. As long as the SW/Mars interaction remain s like that at Venus, the IMF penetrates deep into the Martian ionosphere u nder the `overpressure' conditions. Results of numerical simulations and th eoretical expectations regarding the temporal evolution of the IMF inside t he Venus ionosphere and appearance of superthermal electrons are also revie wed and assessed.