Over the past decade, orbital images of the Martian surface revealed key evidence about the history of the planet environment (craters, faults, paleo-lakes, and rivers), partially hidden under a widespread layer of aeolian deposits. Furthermore, several recent observations and studies support the hypothesis that water could be found in the shallow subsurface of Mars. Low-frequency synthetic aperture radar (SAR) has demonstrated its subsurface imaging capabilities on Earth, especially in arid regions. While SAR potentials for Mars exploration have already been widely discussed, we present here results of a theoretical and parametric study, based on the experience we gained from terrestrial surveys on Mars analog test sites, which evaluates the capabilities of a P-band (430 MHz) SAR for Mars exploration for both shallow subsurface geology mapping and moisture detection. We suggest that a P-band polarimetric SAR can probe the first meters of the Martian subsurface to reveal the dust-covered geology and to monitor moisture changes over large scales.