Nuclear time to mars
There is no improvement in SNMR signal-to-noise with increasing static field where penetration is controlled by aquifer salinity (skin depth). Using small systems of several kilograms and several watts, the exploration depth of SNMR is one to two orders of magnitude smaller than TDEM: the latter can detect water to depths up to a few kilometers, whereas the former is limited to depths of a few tens of meters. As the measured EMF is proportional to the proton-precession frequency, which in turn is proportional to the planet's static magnetic field, SNMR signals are comparatively weak. Surface nuclear magnetic resonance (SNMR) is the only noninvasive geophysical method that responds nearly uniquely to water. However, moist clays or even ores (e.g., massive hematite) will also be electrically conductive and could be mistaken for aquifers on Mars if proper geologic context is lacking. The time domain electromagnetic (TDEM) method has enjoyed wide success in terrestrial groundwater exploration, and the contrast in electrical conductivity between dry overburden and groundwater containing even a small amount of dissolved solids on Mars will yield a robust response.