“The basic trick of LunaH-Map, which I’ll explain in a moment, is that if the ground that the cosmic ray struck contains hydrogen, any upward-going particles will be slower on average than if there’s no hydrogen there. Most lunar soil has no hydrogen, as determined by various missions to the moon. But lunar soil that contains water ice in it will have plenty of hydrogen, since water is hydrogen and oxygen (H2O). So if you can detect particles of certain speeds as you pass over a certain part of the Moon, you can tell whether there’s water ice embedded in the soil.
To explain all this, I need to tell you why particle speeds are sensitive to the presence of hydrogen, and which types of particles are best to measure.”
To explain all this, I need to tell you why particle speeds are sensitive to the presence of hydrogen, and which types of particles are best to measure.”