Ground as a Critical Factor for Schumann Resonances on Mars

Schumann resonances (SR) are global resonances of electromagnetic waves in the range of extremely low frequency (ELF) propagating in a cavity formed by a planetary surface and a lower ionosphere. SR are induced by electrical discharges, which on Earth are associated mainly with lightning. SR were predicted by Winfried Otto Schumann in 1952. Recently, there have been proposed several estimations of the SR parameters on Mars, for example in the works of: Pechony and Price (2004), Molina-Cuberos et al. (2006), Soriano et al. (2007). All techniques used in those studies were adopted from terrestrial models. However, they did not consider any influence of the ground, as the Earth's surface is characterized by high electrical conductivity and has very weak effect on ELF waves propagation. It is commonly assumed that the Martian crust is composed mainly of basaltic materials. On Mars water, which causes significant increase in electrical conductivity of rocks, does not exist in liquid state at the surface. Therefore the Martian ground is believed to be low-conductive one, even to a depth of tens of kilometers. The conductivity profile of the Martian ionosphere also leads to greater than on Earth attenuation of propagating ELF waves. In our study we have developed an analytical method based on the characteristic altitudes formalism that has allowed us to take into consideration the Martian ground. We carried out simulations of two cases, assuming adequately: wet and dry basaltic ground. The results demonstrate that there is a huge difference between these two situations. In the wet case the obtained SR parameters do not considerably differ from those presented in the previous works, which considered only finite ionosphere conductivity, whereas in the dry case they indicate that SR cannot occur on Mars. These results point out the importance of studying SR on Mars and the need for further research in propagation of ELF waves in the Martian environment. SR can be used not only for studying potentially possible electrical discharges on Mars, but also as a remote sensing tool for exploration of the Martian lithosphere. Furthermore, they can be especially useful for groundwater detection.