Caption: 
Concept for a flight version of the Mars Time Domain Electromagnetic Sounder (MTDEM), which uses induction to detect groundwater up to 5 km deep. This illustration shows the MTDEM launcher in its stowed (cruise) and deployed (landed) configurations; spooling projectiles are then ejected using compressed gas, forming a large wire loop on the planet's surface.

Credit: 
Image Courtesy of Southwest Research Institute