A new global map of fault ridges within the Moon's maria reveals that lunar tectonic activity in these dark basalt plains is more extensive than previously understood. Some of these ridges have been dated to a geologically recent few tens of millions of years ago, providing further evidence that the Moon continues to slowly contract, causing its surface to wrinkle.
Findings and Significance
This research indicates that the Moon's dark basalt plains, which are considered prime locations for future missions and potential long-term bases, are not geologically inactive.
Geologist Cole Nypaver of the Smithsonian Institution's Center for Earth and Planetary Studies stated that while the prevalence of lobate scarps in the lunar highlands has been known since the Apollo era, this is the first documentation of similar widespread features throughout the lunar mare. The work contributes to a complete understanding of recent lunar tectonism, offering insights into the Moon's interior, its thermal and seismic history, and the potential for future moonquakes.
While the Moon does not have Earth-like tectonic plates, it exhibits internal activity due to its gradual cooling since its formation approximately 4.5 billion years ago. Surface features known as lobate scarps, found in the rocky lunar highlands, and small mare ridges (SMRs), found in the volcanic basalt plains (maria), are manifestations of this gradual contraction.
Methodology and Results
Researchers, led by Cole Nypaver, utilized high-resolution images from NASA's Lunar Reconnaissance Orbiter (LRO) to map 1,114 previously undocumented SMR segments on the Moon's near side. This mapping effort, combined with earlier surveys, brings the global total to 2,634 SMR segments across both hemispheres.
To determine the formation age of these ridges, researchers used a method of crater counting. Fault slips trigger moonquakes that erase small impact craters nearby. By counting remaining small craters, scientists can estimate the last movement of a fault.
This analysis determined that the SMRs formed between approximately 310 and 50 million years ago, with the youngest dated at about 52 million years old. The average age was approximately 124 million years, comparable to the 105 million-year average for lobate scarps.
Modeling the geometry of the faults allowed the team to estimate their dip and slip, calculating that the lunar maria have contracted by roughly 0.003 to 0.004 percent. This amount is comparable to previously measured contraction in the highlands, suggesting that both terrains are shaped by the same global stresses.
Implications
Geologist Tom Watters of the Center for Earth and Planetary Studies noted that the detection of young, small ridges in the maria and the understanding of their cause complete a global picture of a dynamic, contracting Moon. These findings significantly increase the inventory of potential seismic sources on the Moon, enhancing the understanding of its ongoing evolution.
The widespread presence of recently or currently seismically active tectonic features across the maria presents new opportunities for future lunar missions and investigations. The distribution of SMRs may also be relevant for long-term lunar habitation due to the hazards that shallow moonquakes could pose to human-made lunar infrastructure.
The research was published in The Planetary Science Journal.