How do we know there is water ice on the Moon?

NASA's Clementine in 1994 and Lunar Prospector, which began its mission mapping the Moon this week in 1998, were two of the first missions to find evidence for the existence of water ice on the Moon.

In this visualization of Lunar Prospector's data, high concentrations of hydrogen—a sign of potential ice deposits—are seen around the south pole of the Moon.

Read more about the history of evidence for water on the Moon: go.nasa.gov/4jAZea4