Several newly discovered structures on the far side of the moon were likely caused by relatively recent activity, challenging prior assumptions that the Earth’s only natural satellite stopped experiencing geological activity billions of years ago.
Studies had previously concluded that the large arching ridges found on the moon’s near side were likely caused by heavy compression, most likely tectonic shifts that ended roughly three billion years ago. However, a new analysis by two Smithsonian Institution scientists and a University of Maryland (UMD) geologist focusing on the smaller ridges discovered on the far side of the moon has offered tantalizing hints that the moon may have experienced seismic activity much more recently.
“Many scientists believe that most of the moon’s geological movements happened two and a half, maybe three billion years ago,” said Jaclyn Clark, an assistant research scientist in UMD’s Department of Geology, in a statement. “But we’re seeing that these tectonic landforms have been recently active in the last billion years and may still be active today.”
Team Finds Previously Unknown Ridges on the Far Side of the Moon
When studying the activity below the moon’s surface, scientists are often forced to rely on data collected from features and other components on the surface instead. One of the most analyzed features is the structural ridges within the lunar maria, which are the flat, dark areas on the moon’s surface filled by ancient lava flows. Some of these areas are actually visible to the blind eye.
In their published study, Clark and two colleagues from the Smithsonian Institute combined advanced mapping software and new modeling techniques to analyze previously collected images of the moon’s surface. After some comparison, these techniques revealed the presence of 266 small, previously unknown ridges on the moon’s far side.
According to the study authors, the newly discovered ridges typically appeared in groups of 10 to 40 in ancient volcanic regions that probably formed between 3.2 and 3.6 billion years ago. The ridges also seemed to form in narrow areas that the researchers suspect may lie directly above structural weaknesses in the moon’s surface.
Surprisingly, once the team employed a well-accepted technique called crater counting to estimate the ages of the unusual structures, they found that their original date estimates did not match up with the evidence. Instead, the data seemed to indicate they were formed more recently.
“These small mare ridges seem to have formed within the last 200 million years or so,” Clark said, “which is relatively recent considering the moon’s timescale.”
Specifically, the team found that the ridges’ smaller sizes and lower concentrations were more consistent with recent activity. Some of the ridges also seemed to have occurred after recent meteor impacts instead of billions of years in the past.
“Essentially, the more craters a surface has, the older it is; the surface has more time to accumulate more craters,” Clark explained. “After counting the craters around these small ridges and seeing that some of the ridges cut through existing impact craters, we believe these landforms were tectonically active in the last 160 million years.”
Understanding Lunar Seismic Activity is Critical for Planning Future Moon Missions
In the study’s conclusion, the researchers point out that the newly discovered structures on the far side of the moon were overall structurally “similar” to those found on the near side. They suspect this similarity suggests they were made by similar forces, including the shifts in the lunar orbit and the moon’s ongoing shrinking. They also suspect that the shallow “moonquakes” detected by NASA’s 20th-century Apollo missions might hint at the seismic activity behind the ridges’ creation.
While their study does not conclusively prove recent seismic activity on the moon, the researchers believe that understanding the moon’s past and current geological activity is critical to mission planners and future potential colonists who may call it their home. They also say that additional research into the structures found on the far side of the moon can help with this effort, including equipping astronauts with the tools needed to study this activity more closely.
“We hope that future missions to the moon will include tools like ground penetrating radar so researchers can better understand the structures beneath the lunar surface,” Clark said. “Knowing that the moon is still geologically dynamic has very real implications for where we’re planning to put our astronauts, equipment, and infrastructure on the moon.”
The study “Recent Tectonic Deformation of the Lunar Far Side, Maria and South Pole Aitken Basin” was published in The Planetary Science Journal.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.