The Moon's permanently shadowed regions, or PSRs, are places on the Moon that haven't seen the Sun in millions, or even billions, of years. The Earth's tilted axis allows sunlight to fall everywhere on its surface, even at the poles, for at least part of the year. But the Moon's tilt relative to the Sun is only 1.6°, not enough to get sunlight into some deep craters near the lunar north and south poles. PSRs are therefore some of the coldest, darkest places in the solar system.
Because of that, PSRs are expected to be excellent traps for volatiles, chemicals that would normally vaporize and escape into space, and this includes water. Lunar Reconnaissance Orbiter (LRO) includes several instruments designed to peer into the PSR darkness and measure temperature, reflectivity, and neutron absorption, all of which are clues to what chemicals might be hiding there. This animation shows where the PSRs are and in what ways LRO can see inside them.
A close flyover of south pole terrain. Elevation contours light up, and as we arrive at Shackleton crater, elevation color coding lights up inside it and in other permanently shadowed regions. Finally, the view pans up into the sky, revealing a rich starfield.
Three different datasets are overlaid on the south pole. For each, the full dataset fades to a version masked by the permanent shadow map. The datasets are from LAMP (lyman alpha albedo), Diviner (daytime temperature), and LEND (hydrogen).