Curiosity’s Dynamic Albedo of Neutrons, or DAN, detects hydrogen associated with water or ice near the Martian surface. It can investigate subsurface material without needing to drill into it.
DAN works by sending pulses of high-energy neutrons into the ground and measuring how the neutrons return. Hydrogen changes the neutron signal, allowing scientists to estimate the amount and depth of hydrogen-bearing material beneath the rover. Because water ice and hydrated minerals contain hydrogen, DAN is a valuable tool for studying near-surface water.
The instrument includes a detector and a pulsing neutron generator. Curiosity’s science team can use DAN both while the rover is moving and when it pauses at a target, building a subsurface picture along the route through Gale crater.
The other choices have different jobs: Mastcam provides panoramic and multispectral imaging, MAHLI takes close-up images of rocks and soil, and RAD measures radiation. DAN does not directly photograph water; it infers hydrogen-rich material from neutron behavior.