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"Lunar ice" might sound a little strange to many people, but it didn't sound so strange to three Caltech researchers who, in 1961, suggested a few plausible arguments for its existence. The three (Kenneth Watson, Bruce C. Murray, and Harrison Brown) theorized that, since the Sun never deviates more than 1.6° from the Moon's equatorial plane, some crater floors near the lunar poles might lie in constant shadow. At 40° to 50° Kelvin, these "cold traps" could keep ice so solidly frozen that almost none of it would escape into space.

Thirty-three years later, their theory was tested for the first time.


Blazing a Trail: Follow the trail of events and ideas that cleared the way for Prospector's journey into the new frontier.

Staking a Claim: If we find ice, who's is it? Explore the questions and concerns surrounding the advent of interstellar real estate.

Mining the Gold: Take a look at the ways a lunar motherload might change the way we think about humans in space.

Eureka: Lunar Prospector finds ices at the lunar poles.