Neutrons reveal a new view of Mars

8 March 2002

Display high-resolution version

Seventy years after the discovery of the neutron, scientists are using this common constituent of most matter to reveal the amount of hydrogen in the surface of the planet Mars. In February 1932, James Chadwick at Cambridge University in the UK, published* his evidence for the existence of an uncharged constituent with atomic nuclei - the neutron. He was awarded the Nobel prize for this achievement three years later in 1935. Since then neutrons have been used in many ways, perhaps most famously for their role in the nuclear chain reaction at work in a nuclear reactor or in an atomic bomb. However neutrons are nowadays used in many ways to study the the structure of materials.

This week's image shows the number of neutrons emitted by the soil of Mars, as measured by the spacecraft Mars Odyssey exactly 70 years after Chadwick's discovery. Neutrons are emitted when cosmic rays strike the surface, but hydrogen in the surface can slow down and absorb the neutrons. Deep blue colors on the map indicate soil enriched in hydrogen, where a low intensity of intermediate-energy, or epithermal, neutrons is found. The presence of hydrogen on Mars is important because it is one of the two constituents of water.

(*see Nature 129 312 (1932)

Credit: NASA/JPL/University of Arizona

Please contact person or institution named for information about permission for public or commercial use.