When the Moon split from the Earth around 4.53 billion years ago, the Solar System was tumultuous and hot. The Moon has been cooling from this ever since, and as it does, the interior contracts. This causes splitting and movement in the Moon’s surface, creating a scarred, fractured landscape, like areas of high seismic activity on Earth.
Thousands of small fault lines have been detected on the surface of the Moon by the Lunar Reconnaissance Orbiter (LRO), where the contraction of the Moon’s centre has caused cracking and movement of the crust. Furthermore, the tidal force exerted on the Moon by the Earth causes movement of the Moon’s surface, creating more cracks and fault lines.
The Apollo astronauts set up a series of seismometers (the Apollo Passive Seismic Network), detecting shallow moonquakes as the Moon’s centre contracts and initiates movement. The largest of these quakes had its epicentre on the Moon’s South polar region, near a proposed landing site for Artemis III, the first crewed Moon landing mission of NASA’s Artemis program and the first crewed American lunar landing since Apollo 17 in 1972. This next mission is widely expected to carry the first woman to the surface of the Moon.
This discovery has important implications for future missions and exploration. Perhaps future Moon-based settlements will have to quake-proof their buildings and prepare for seismic events like we do in earthquake zones on our home planet.
The placement of permanent outposts on the Moon must be carefully considered to mitigate the risk of moonquakes. To fully understand the future of lunar habitation, more seismic measurements must be taken across the surface of the Moon, not just at its south pole.