Story highlights Lost Apollo mission tapes were recovered to solve a lunar mystery

Astronauts effectively helped heat up the moon at experiment sites

(CNN) NASA's Apollo missions in the 1960s and '70s served not only to land Americans on the lunar surface but to answer key questions about the moon that could be answered only by going there.

As often happens, those answers sometimes stirred up more questions -- or, as in this case, an abiding mystery.

During the Apollo 15 and 17 missions in 1971 and 1972, astronauts installed probes at two sites to measure the moon's temperature below the surface. The Apollo program ended in 1972, but raw data on the temperature of the moon's surface, as well as a few meters below it, was transmitted from the probes and recorded on magnetic tapes at NASA's Johnson Space Center in Houston from 1971 to 1977.

In 1974, the subsurface of the moon unexpectedly rose in temperature by 1.8 degrees to 3.6 degrees Fahrenheit near the probes. The possible reasons for this change were debated by planetary scientists for decades. The mystery was only deepened by lost mission tapes that would account for temperature data from 1975 to 1977.

For the past eight years, a team of researchers has dedicated themselves to recovering the lost data and solving the mystery. Now, their findings and recovered Apollo mission data that weren't previously well-publicized can see the light of day. The study was published this month in the American Geophysical Union's Journal of Geophysical Research: Planets

Apollo 17 mission commander Eugene Cernan drives the lunar roving vehicle.

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