Gamma Ray Spectrometer - Planetary Gamma-ray Spectrometers

Planetary Gamma-ray Spectrometers

Gamma-ray spectrometers have been widely used for the elemental and isotopic analysis of airless bodies in the Solar System, especially the Moon and Mars. These surfaces are subjected to a continual bombardment of high-energy cosmic rays, which excite nuclei in them to emit characteristic gamma-rays which can be detected from orbit. Thus an orbiting instrument can in principle map the surface distribution of the elements for an entire planet. Examples include the mapping of 20 elements observed in the exploration of Mars, the Eros asteroid and the Moon. They are usually associated with neutron detectors that can look for water and ice in the soil by measuring neutrons. They are able to measure the abundance and distribution of about 20 primary elements of the periodic table, including silicon, oxygen, iron, magnesium, potassium, aluminum, calcium, sulfur, and carbon. Knowing what elements are at or near the surface will give detailed information about how planetary bodies have changed over time. To determine the elemental makeup of the Martian surface, the Mars experiment used a gamma ray spectrometer and two neutron detectors.

GRS instruments supply data on the distribution and abundance of chemical elements, much as the Lunar Prospector mission did on the moon. In this case, the chemical element thorium was mapped, with higher concentrations shown in yellow/orange/red in the left-hand side image shown on the right.