The Dynamic Albedo of Neutrons tool, called DAN for short, looks for telltale changes in the energies of neutrons released from Martian subsurface that indicate how much water is chemically bound in the soil or rocks.
|Main Job||Search for signs of water by measuring the hydrogen in the ground below. Detections of hydrogen may indicate the presence of water bound in minerals.|
|Location||On the aft-port-side of the rover "body."|
|Capability||Measures subsurface hydrogen up to one meter (three feet) below the surface.|
|Sensitivity||Can detect water content as low as 1/10th of 1 percent.|
One way to look for water on Mars is to look for neutrons escaping from the planet's surface. Cosmic rays from space constantly bombard the surface of Mars, knocking neutrons in soils and rocks out of their atomic orbits. If water happens to be present, hydrogen atoms slow the neutrons down. In this way, some of the neutrons escaping into space have less energy and move more slowly. These slower particles can be measured with a neutron detector.
The DAN instrument tracks the abundance of minerals that have molecules of water in their crystal structures along the rover’s traverse. At the request of the Russian Federal Space Agency, the Mars Science Laboratory rover carries a pulsing neutron generator called the Dynamic Albedo of Neutrons, which is sensitive enough to detect water content as low as one-tenth of 1 percent. Albedo is a scientific word for the reflection or scattering of light. Funded by the Russian government, the instrument pulses the Martian surface with neutrons from a height of 2.6 feet (about 80 cm). The neutrons travel 1-2 feet (about half of a meter) below the surface before being scattered back to DAN’s detectors.
If the beam of neutrons encounters a layer of hydrogen-bearing material beneath the surface, DAN will detect a relatively greater number of slower neutrons reflected at the surface. If there are no such layers beneath the surface, DAN will detect a relatively greater amount of faster neutrons reflected at the surface.