Hunting Moon Water With Neutrons

Hunting Moon Water With Neutrons By Mark Thompson - March 27, 2026 04:17 PM UTC | Planetary Science If you want to live on the Moon, you need water. Not just for drinking though since water can be split into hydrogen and oxygen to make rocket fuel and breathable air. Carrying enough of it from Earth for any serious long term mission would be impossibly expensive. But the Moon may already have what future explorers need, locked away as ice in the permanently shadowed craters near its south pole. Finding it precisely and reliably, in enough quantity to be useful is the challenge facing mission planners. And NASA thinks it has exactly the right tool for the job. The Neutron Spectrometer System, or NSS, is a compact instrument that can detect the presence of hydrogen underground without drilling a single hole. Hydrogen, of course, is the H in H₂O so find it, and you've likely found water. NASA is providing the NSS to LUPEX, a lunar rover mission led jointly by Japan's JAXA and India's ISRO, due to arrive at the Moon's south pole no earlier than 2028. Components of the Neutron Spectrometer System undergo testing on the vibration table (Credit : NASA) The Moon's surface is constantly bombarded by cosmic rays which knock neutrons loose from the lunar soil. Those neutrons rattle around underground and eventually escape into space, but when they encounter hydrogen atoms, something interesting happens. Hydrogen and neutrons are almost identical in mass, making them remarkably efficient at exchanging energy in a collision. Hydrogen rich soil absorbs more medium energy neutrons, so fewer escape. A deficit of these neutrons at the surface is a tell tale sign of hydrogen buried below. The NSS detects these escaping neutrons using tubes filled with helium-3, a rare gas exquisitely sensitive to neutron interactions. When a neutron strikes a helium-3 atom, it produces an electrical pulse that can be counted and analysed, building up a picture of hydrogen concentration down to a dept...