No other world in the Solar System exhibits the plate tectonics and quakes akin to Earth’s, yet that doesn’t imply their ground remains undisturbed. Lunar seismic activity has been known since the Apollo era, and for approximately the last fifteen years, evidence has pointed toward the Moon shrinking, losing 50 meters in radius over the last 200 million years. Fresh data now corroborates these prior findings. The paper detailing these results was published in The Planetary Science Journal.
In its past, the Moon possessed significantly greater geological dynamism, but over time, its interior began to cool and solidify. As the inner core contracts, the outer crust cracks and deforms. Faults associated with this process, termed thrust faults, were identified by Tom Watters and his colleagues within the lunar highlands—the Moon’s bright, light-gray regions.
New surveys of the Moon have brought to light small wrinkle ridges (SWRs)—fractures situated in the lunar maria, which are the dark, basaltic plains of the Moon. These maria are what we commonly refer to as seas, for instance, the Sea of Tranquility where Apollo 11 landed.
The team finalized an inventory of small craters, cataloging 1114 new ones, bringing the total count to 2634. Both the small craters and the thrust faults are closely related in age: averaging 124 million years and 105 million years, respectively. Furthermore, the group observed that they are frequently physically interconnected where the terrain transitions from highlands to maria. Lunar contraction is the most plausible driver for both phenomena.
“Our discovery of young, small ridges in the maria, and understanding their source, completes the global picture of a dynamically shrinking satellite,” commented study co-author Watters from the Center for Earth and Planetary Studies.
“While the ubiquity of thrust faults across the lunar highlands has been recognized since Apollo, this marks the first time scientists have documented these structures so extensively across the lunar visage,” added lead author Cole Nypaver, also affiliated with the Center for Earth and Planetary Studies. “This work advances our comprehensive insight into recent lunar tectonics, which will contribute to a deeper comprehension of its internal structure, thermal and seismic history, and the potential for future moonquakes.”
Upcoming crewed and robotic explorations of the Moon are set to yield novel and more granular data regarding its interior workings. NASA’s Artemis program aims to land humans on the lunar surface before the close of this decade (though certain hurdles exist). Artemis II is anticipated to launch in the coming weeks, allowing astronauts to orbit the Moon and view areas previously inaccessible to humans.
“We are living in an incredibly exhilarating era for lunar science and exploration,” Nypaver continued. “Upcoming lunar exploration initiatives, such as Artemis, are poised to deliver a wealth of fresh intelligence about our satellite. A finer grasp of lunar tectonics and seismic behavior will directly influence the safety and scientific success of these and all subsequent missions.”
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