After several years of extracting and analyzing data from the archaic tape reels, the researchers discovered that probes planted near the moon’s surface recorded a greater and faster temperature jump than the probes planted deeper down found. This indicated that the temperature spike was beginning at the surface and not within the moon itself, the researchers said.

A quick study of lunar surface photos taken by the Lunar Reconnaissance Orbiter Camera provided another crucial clue. The photos showed that areas near the Apollo landing sites were crisscrossed with dark streaks where the astronauts had walked or driven about the moon’s surface, apparently kicking a lot of ancient dust aside.

In fact, the researchers said, the mere act of installing the temperature probes may have thrown off those probes’ measurements by altering the surface environment around the instruments — and significantly increasing the surface’s temperature.

“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,” Nagihara told the American Geophysical Union. “That kind of consideration certainly goes in to the designing of the next generation of instruments that will be someday deployed on the moon.”

Originally published on Live Science.