Moon is not as 'geologically dead' as previously thought

However, a new study reveals that what lies beneath the lunar surface may be more dynamic than previously believed. Two Smithsonian Institution scientists and a University of Maryland geologist discovered that small ridges located on the moon's far side were notably younger than previously studied ridges on the near side. Their findings were published in The Planetary Science Journal on January 21, 2025.

"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. "But we're seeing that these tectonic landforms have been recently active in the last billion years and may still be active today. These small mare ridges seem to have formed within the last 200 million years or so, which is relatively recent considering the moon's timescale."

Using advanced mapping and modeling techniques, the team found 266 previously unknown small ridges on the moon's far side. The ridges typically appeared in groups of 10 to 40 in volcanic regions that likely formed 3.2 to 3.6 billion years ago in narrow areas where there may be underlying weaknesses in the moon's surface, according to the researchers. To estimate the age of these small ridges, the researchers used a technique called crater counting. They found that the ridges were notably younger than other features in their surroundings.

"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."

Interestingly, Clark noted that the far-side ridges were similar in structure to ones found on the moon's near side, which suggests that both were created by the same forces, likely a combination of the moon's gradual shrinking and shifts in the lunar orbit. The Apollo missions detected shallow moonquakes decades ago; the new findings suggest that these small ridges might be related to similar seismic activity. Learning more about the evolution of the lunar surface could have important implications for the logistics of future moon missions.

"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."