News study says thermal moonquakes occurs twice day

A new analysis of seismic activity on the Moon used machine learning to re-analyze archival data of "moonquakes" collected during the Apollo era, a press statement reveals.

Specifically, the new study applied these techniques to old moonquake data from the Apollo 17 mission, Interesting Engineering reports. 

It found that previous analyses had mischaracterised a surprising source of vibrations — the Apollo 17 lunar lander base.

Machine learning casts a new eye on Apollo data

The researchers, who published a new paper in the Journal of Geophysical Research - Planets, specifically looked at eight month's worth of data of thermal moonquakes collected by an array of three seismometers during the Apollo 17 mission in 1972.

Thermal moonquakes are caused when massively fluctuating temperatures — swinging as high as 250 degrees F and -208° F — on the Moon cause the lunar surface to expand and contract, leading to small tremors and cracking.

The new research shows that thermal moonquakes occur with precise regularity every afternoon as the Moon begins to cool off. However, the analysis also detected additional signatures of seismic activity in the morning that differed from the evening moonquakes.

The researchers triangulated the source of this extra data and found that the tremors in the morning came from the Apollo 17 lunar lander base. The structure, located a few hundred meters away, heated and expanded in the morning, and the seismic array picked up the resulting vibrations.

"Every lunar morning when the sun hits the lander, it starts popping off," Allen Husker, research professor of geophysics and co-author on the new study, explained in the statement. "Every five to six minutes, another one, over five to seven Earth hours. They were incredibly regular and repeating."

Detecting seismic activity on the Moon

NASA aims to eventually establish a permanent presence on the Moon with its Artemis program, and future Artemis missions are expected to send new seismometer technologies to the lunar surface.

Detecting seismic activity on the Moon can teach scientists a great deal about materials under the lunar surface and other important information for future lunar missions.

"We will hopefully be able to map out the subsurface cratering and to look for deposits," Husker continued.

"There are also certain regions in craters at the Moon's South Pole that never see sunlight; they are permanently shadowed," he said. "If we could put up a few seismometers there, we could look for water ice that may be trapped in the subsurface; seismic waves travel slower through water."

Ultimately, this work could also help answer a lot of open questions about the Moon's internal structure.

"It's important to know as much as we can from the existing data so we can design experiments and missions to answer the right questions. The Moon is the only planetary body other than the Earth to have had more than one seismometer on it at a time. It gives us the only opportunity to thoroughly study another body," Husker explained.