Moon Not as ‘Geologically Dead’ as Previously Thought, Study Reveals

Our planet’s biggest satellite shows what seems like an unchanging face—the man in the moon never cracks a smile, after all—but a new study from a team including a University of Maryland researcher reveals that there’s more going on beneath the lunar surface than previously believed.

In results reported earlier this month in The Planetary Science Journal, two Smithsonian Institution scientists and a UMD geologist discovered that features located on the moon’s far side were notably younger than similar landforms previously studied on the near side—findings that could have implications for future human exploration of the moon.

“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. “But we're seeing that these tectonic landforms have been recently active in the last billion years and may still be active today.”

Researchers have studied the moon’s surface for decades to help piece together its complex geological and evolutionary history. Evidence from the lunar maria (dark, flat areas filled with solidified lava) suggested that the moon experienced significant shrinking in its distant past. Researchers suspected that large, arching ridges on its near side were formed by contractions that occurred billions of years ago—concluding that the moon’s maria has remained dormant ever since.

Using advanced mapping and modeling techniques, the team found 266 previously unknown small ridges on the moon’s far side that called that view into question. The ridges typically appeared in volcanic regions that likely formed 3.2 to 3.6 billion years ago in areas where there may be underlying weaknesses in the moon’s surface, according to the researchers. To estimate the ridges’ age, the researchers used a technique called crater counting that showed the features 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.

“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.”