Researchers have established the inaugural comprehensive global cartography of fault lineaments within the Moon’s mare regions. This endeavor illuminates that tectonic dynamics across these vast, dark basaltic expanses are demonstrably more prevalent than heretofore understood.
Furthermore, certain of these raised features exhibit ages as recent as a few tens of millions of years – an exceptionally brief period in cosmological chronology. This presents an unprecedentedly clear visualization of the Moon’s continuous, albeit gradual, contraction, causing its surface to pucker and crease akin to desiccated fruit.
These revelations imply that the Moon’s extensive basaltic plains, which represent primary candidates for future exploratory endeavors and the establishment of enduring settlements, are far from being geologically quiescent.
“Since the seminal Apollo missions, the ubiquity of lobate scarps within the lunar highlands has been recognized. However, this marks the initial instance where scientists have systematically documented the widespread dissemination of analogous structures across the lunar mare,” states geologist Cole Nypaver, affiliated with the Smithsonian Institution’s Center for Earth and Planetary Studies in the United States.
“This investigative work facilitates a holistic global comprehension of recent lunar tectonic activity, ultimately fostering a more profound understanding of its internal composition, thermal evolution, seismic history, and the potential for lunar seismic events.”
Prior investigations had pinpointed comparable ridges in geographically isolated sectors. Nevertheless, this research represents the first instance of their global mapping and analysis within the context of a unified contractional system.
While the Moon lacks the mobile tectonic plates characteristic of Earth, it nonetheless exhibits intrinsic geophysical processes. Originating approximately 4.5 billion years ago as a molten, incandescent mass, it has been progressively cooling throughout its existence.
Manifestations of this ongoing thermal dissipation are observable in surface formations designated as lobate scarps. These are elevated, ridge-like structures that extensively punctuate the rugged lunar highlands. However, these features do not constitute the sole evidence of the Moon’s incremental dimensional reduction.
Within the lunar maria—vast, planar expanses of dark volcanic basalt—the Moon also undergoes surface deformation. These formations are identified as small mare ridges (SMRs), which are compressional tectonic elements generated by shallow thrust faulting within the dark mare basalts.
These SMRs appear to have originated concurrently with the lobate scarps. However, their spatial distribution and correlation with the Moon’s persistent contraction had not been definitively established, prompting Nypaver and his team to undertake this precise objective.
Leveraging high-resolution imagery acquired by NASA’s Lunar Reconnaissance Orbiter, the research group meticulously identified 1,114 previously uncatalogued SMR segments on the Moon’s near side. When aggregated with data from prior surveys, this brings the total global count to 2,634 SMR segments distributed across both the near and far lunar hemispheres.
Subsequently, the investigators diligently determined the temporal origins of these ridges. Direct age determination of the ridges is unfeasible. However, the surrounding geological context provides a reliable chronometric framework. The slippage along these fault lines induces lunar seismic events of sufficient magnitude to obliterate minute impact craters in their immediate vicinity. By enumerating the residual small craters, scientists can ascertain the approximate timing of the last fault displacement.
Employing this methodology, the researchers concluded that the SMRs originated between approximately 310 and 50 million years ago, with the most recent formations dating to around 52 million years in the past. The mean age was calculated to be approximately 124 million years, closely aligning with the average age of 105 million years attributed to the lobate scarps.
To quantitatively assess the Moon’s volumetric contraction, the team also constructed models of the fault geometries, estimating their subsurface inclination and the magnitude of displacement. Based on these calculations, it was determined that the lunar maria have undergone a contraction of roughly 0.003 to 0.004 percent. While seemingly minuscule, this magnitude is commensurate with the degree of contraction previously quantified in the highland regions.
This concordance suggests that analogous global stresses are instrumental in shaping both topographical regimes. The Moon’s ongoing shrinkage has imprinted its signature upon both the rugged highlands and the placid, dark volcanic plains.
“Our identification of recent, diminutive ridges within the maria, coupled with our elucidation of their causative mechanisms, completes a comprehensive global depiction of a dynamically contracting lunar body,” asserts geologist Tom Watters, also of the Center for Earth and Planetary Studies.
These findings substantially augment the repository of potential seismic sources on the Moon, thereby enhancing our analytical capabilities for comprehending the Moon’s continuous evolutionary trajectory.
“The extensive prevalence of recently or presently seismically active tectonic features across the mare regions furnishes novel research avenues for forthcoming lunar missions and scientific investigations,” the research authors articulate within their published work.
“Furthermore, the spatial distribution of SMRs may hold significance pertinent to any long-term human presence on the Moon, given the extant hazards posed by shallow lunar seismic activity to artificial lunar infrastructure.”
