The Rover Environmental Monitoring Station is Curiosity’s weather station. It has been designed to record six atmospheric parameters: wind speed/direction, pressure, relative humidity, air temperature, ground temperature, and ultraviolet radiation.
REMS instrument. Image: JPL
The Radiation Assessment Detector (RAD)
The Radiation Assessment Detector will determine the radiation dose for humans on the surface of Mars. It will monitor high-energy atomic and subatomic particles from the sun, from distant supernovas and from other natural sources. These particles are natural radiation that could be harmful to astronauts on a Mars mission or to any microbes near the surface of Mars.
RAD instrument. Image Credit: NASA/JPL-Caltec
Video on RAD measurements:
Dynamic Albedo of Neutrons (DAN)
Dynamic Albedo of Neutrons (DAN) is a detector for measuring hydrogen or ice and water near the Martian surface. DAN shoots neutrons into the ground and measures the timing and energy levels of neutrons reflected back up. The below image shows the location of the two components of the Dynamic Albedo of Neutrons instrument. The neutron generator is mounted on the right hip (visible in this view), and the detectors are on the opposite hip
Location of DAN instrument. Image: NASA
If liquid or frozen 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. The detector will use this characteristic to search for subsurface ice on Mars.
DAN shoots neutrons into the ground and measures the time/energy of reflections back to the instrument. Image Credit: NASA
The diagram below depicts the case of a neutron that does not collide with any hydrogen atoms before it reaches DAN's detector. It is detected in a characteristically short time -- about one millisecond -- after being emitted by DAN's neutron generator, and with a characteristic energy.
Illustration of a neutron which does not collide with hydrogen atoms. Image Credit: NASA/JPL-Caltech/RSRI
This next diagram illustrates the case of a neutron that does collide with hydrogen in the ground. Collisions with hydrogen nuclei -- like two billiard balls -- result in a change in energy level and a change in the time interval between when the neutron is emitted by DAN's neutron generator and when it reaches DAN's detector, compared with neutrons that do not collide with hydrogen, as in the companion diagram.
Notice the collisions with hydrogen introduce a delay. Image: NASA/JPL-Caltech/RSR