Ice Surface of the Moon

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Temperatures on most of the Moon’s surface are too extreme for water or ice to exist, ranging from a maximum of 127°C (261°F) at lunar noon to a minimum of -173°C (-279°F) just before lunar dawn. Temperatures in permanently shadowed areas near the lunar poles, however, may consistently be as low as -220°C (-364°F). In 1996 a team working with data gathered by the Clementine spacecraft announced that frozen water may exist in one of these shadowed areas near the Moon’s south pole. Clementine was a joint venture by the Department of Defense and the National Aeronautics and Space Administration (NASA). The spacecraft’s radar showed what may be an 8,000 sq km (3,000 sq mi) area covered with a mixture of dirt and ice crystals. Clementine was launched in 1994 and gathered data for four months.

NASA launched the Lunar Prospector spacecraft toward the Moon in 1998. Prospector returned data confirming the Clementine discovery and suggesting that a significant amount of water exists in the dark areas near the lunar poles in the form of ice crystals mixed with soil. Estimates of the amount of water on the Moon vary widely, from 10 million to 6 billion metric tons.

In 1999, at the end of the Lunar Prospector’s mission, scientists programmed the spacecraft to crash at a specific spot likely to contain water, hoping that the debris that rose with the impact would contain detectable water vapor. Although no water was detected after the crash, scientists could not conclude that no water existed on the Moon. They acknowledged several other possible explanations for the result: The spacecraft might have missed its target area, the telescopes used to observe the crash might have been aimed incorrectly, or the magnitude of the impact created by the Lunar Prospector spacecraft may have been insufficient to generate a large cloud of water vapor.

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