Lost Moon Tapes Help Solve Decades-Old Lunar Mystery

The 1970s had a profound effect on Earth. But the “Me Decade” also left an impression on the Moon.

Scientists believe they have solved a 40-year-old mystery of why the lunar subsurface warmed slightly during the Apollo missions.

NASA’s third human spaceflight program, active between 1969 and 1972, saw 12 men walk on the moon—including pioneers Neil Armstrong and Buzz Aldrin.

But while U.S. astronauts were making history, they were also disrupting a celestial ecosystem.

During the Apollo 15 and Apollo 17 missions, rocketeers conducted heat flow experiments (HFEs) by deploying probes on the Moon to measure the satellite’s internal temperatures.

Astronaut Harrison Schmitt uses an adjustable sampling scoop to retrieve lunar samples during the Apollo 17 mission (via NASA)

Scientists hopes these measurements would shed light on whether the Moon’s core was hot like Earth’s, and how much heat the rocks of its crust and mantle could generate.

The raw temperature data was transmitted from space to NASA’s Johnson Space Center in Houston, where it was recorded on open-reel magnetic tapes. Those tapes were then analyzed and archived.

But when the experiments ended in 1977, only tapes from 1971 to ’74 were archived at Goddard Space Flight Center’s National Space Science Data Center. The rest—presumably still under examination—were never filed; three years of information was lost to time.

Until now.

A team of researchers recovered and restored major portions of the previously unarchived data from January 1975 to September 1977; their findings are detailed in a paper published by the American Geophysical Union’s Journal of Geophysical Research: Planets.

Spoiler alert: The missing tapes were gathering dust at the Washington National Records Center, which stored documents for various U.S. federal agencies.

The borestem and cable of the Apollo 15 heat flow probe 1 (left) and Apollo 17 probe 2 (via NASA)

It turns out that by walking and driving a rover over the Moon’s previously unsullied surface, astronauts destroyed its equilibrium. As a result, the satellite reflected less of the Sun’s light back out to space, raising the temperature 1-2 degrees Celsius (1.8-3.6 degrees Fahrenheit).

“In the process of installing the instruments you may actually end up disturbing the surface thermal environment of the place where you want to make some measurements,” lead study author Seiichi Nagihara, a planetary scientist at Texas Tech University, said in a statement.

In hindsight, it seems obvious that shoving tools into the ground could upset the space environment. At least we can learn from our mistakes; this is certainly something for future lunar missions to think about.

“That kind of consideration certainly goes into the designing of the next generation of instruments that will be someday deployed on the Moon,” Nagihara added.

A Lunar Reconnaissance Orbiter Camera (LROC) image of the vicinity of the Apollo 17 landing site (via NASA)

By pairing the newly discovered data with images of the Moon’s surface from the Lunar Reconnaissance Orbiter, researchers were also able to map astronaut activity. Surface disturbance darkened the lunar soil, which absorbs more light from the sun, making it warmer.

“It doesn’t take much disturbance to get that very subtle warming on the surface, Nagihara said. “So analysis of the historic data together with the new images of the Moon really helped us characterize how the surface warmed.”

[embedded content]