Though it's now widely accepted that water (in the form of ice) exists on the Moon, it took multiple missions over the course of the last two decades for scientists to reach this conclusion. A Columbia University astrophysicist, however, says that the Soviet space program had found evidence of lunar water as early as 1976. According to Professor Arlin Crotts, the unmanned Luna 24 mission brought back geological samples that contained about 0.1 percent water by mass, taken from the Mare Crisium region of the Moon. These results were published in the Soviet journal Geokhimiia in 1978, under the English title "Possible Water in Luna 24 Regolith from the Sea of Crises."

Although they allowed for some possibility of contamination, the researchers were apparently confident in their results. In the West, however, Geokhimiia was little-read, and Crotts says the Luna 24 mission's results have never been cited in modern academic work. Meanwhile, the American Apollo missions brought back huge numbers of samples, but many were exposed to potential contamination from Earth, meaning that they could not be credibly used to test for water. The Soviet team urged others to follow up on its results, but the Luna 24 probe was the last successful mission in its program. Instead, the world would have to wait for the 1994 Clementine Moon mission for the question to be raised again.

Crotts has called attention to the Luna 24 mission before, but it's now receiving more attention as he concludes a three-part series on water on the Moon in Astronomical Review. The first part, which outlines the history of the subject (including the Luna probe), is available here.