The moon is shrinking, causing moonquakes at the lunar south pole

The moon was long thought to be geologically dead, with no processes occurring inside its core.  But increasing evidence over the last decades suggests that the moon isn’t static and could, in fact, still be tectonically active. Now, new research from NASA suggests that the shrinking of the moon over time is causing moonquakes and the formation of faults near its south pole.

The research is part of NASA’s interest in the lunar south pole, given the agency’s intention to send astronauts there. Researchers have modeled lunar activity to look for the source of moonquakes seen during the Apollo missions.

The epicenter of one of the strongest moonquakes recorded by the Apollo Passive Seismic Experiment was located in the lunar south polar region. However, the exact location of the epicenter could not be accurately determined. A cloud of possible locations (magenta dots and light blue polygon) of the strong shallow moonquake using a relocation algorithm specifically adapted for very sparse seismic networks are distributed near the pole. Blue boxes show locations of proposed Artemis III landing regions. Lobate thrust fault scarps are shown by small red lines. The cloud of epicenter locations encompasses a number of lobate scarps and many of the Artemis III landing regions.
The epicenter of one of the strongest moonquakes recorded by the Apollo Passive Seismic Experiment was located in the lunar south polar region. However, the exact location of the epicenter could not be accurately determined. A cloud of possible locations (magenta dots and light blue polygon) of the strong shallow moonquake using a relocation algorithm specifically adapted for very sparse seismic networks are distributed near the pole. Blue boxes show locations of proposed Artemis III landing regions. NASA/LROC/ASU/Smithsonian Institution

“Our modeling suggests that shallow moonquakes capable of producing strong ground shaking in the south polar region are possible from slip events on existing faults or the formation of new thrust faults,” said lead researcher Tom Watters of the Smithsonian Institution in a statement. “The global distribution of young thrust faults, their potential to be active, and the potential to form new thrust faults from ongoing global contraction should be considered when planning the location and stability of permanent outposts on the Moon.”

Evidence of this movement also comes from the Lunar Reconnaissance Orbiter (LRO), an orbiting spacecraft that takes images of the moon’s surface using its camera. These images show small, young faults that form cliff-like structures.

Lunar Reconnaissance Orbiter Camera (LROC), Narrow Angle Camera (NAC) mosaic of the Wiechert cluster of lobate scarps (left pointing arrows) near the lunar south pole. A thrust fault scarp cut across an approximately 1-kilometer (0.6-mile) diameter degraded crater (right pointing arrow).
Lunar Reconnaissance Orbiter Camera (LROC), Narrow Angle Camera (NAC) mosaic of the Wiechert cluster of lobate scarps (left pointing arrows) near the lunar south pole. A thrust fault scarp cut across an approximately 1-kilometer (0.6-mile) diameter degraded crater (right-pointing arrow). NASA/LRO/LROC/ASU/Smithsonian Institution

The faults are forming due to activity beneath the surface as the moon’s interior cools, causing it to shrink overall. The gravity of Earth also contributes by creating tidal forces that affect the moon’s interior.

This could create activity like landslides on the lunar surface, which could cause problems for future astronauts. Experts say that they need to perform more research into this activity on the moon to choose the best location for landing any future crewed missions there.

“To better understand the seismic hazard posed to future human activities on the Moon, we need new seismic data, not just at the South Pole, but globally,” said another researcher, Renee Weber of NASA’s Marshall Space Flight Center. “Missions like the upcoming Farside Seismic Suite will expand upon measurements made during Apollo and add to our knowledge of global seismicity.”

The research is published in The Planetary Science Journal.

Editors’ Recommendations