Astronauts aboard the Space Shuttle Discovery recorded this rarely seen phenomenon of the full Moon partially obscured by the atmosphere of the Earth. The image was recorded with an electronic still camera at e15:15:15 GMT, Dec. 21, 1999. Credit: NASA, Public domain, via Wikimedia Commons.

The Moon is not as ‘geologically dead’ as previously thought according to new recent which suggests relatively recent activity.

Scientists 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 on the Moon filled with solidified lava) suggested that the Moon experienced significant compression in its distant past.

Researchers suspected that large, arching ridges on the Moon’s near side were formed by contractions that occurred billions of years ago – concluding that the Moon’s maria has remained dormant ever since. 

Close up of a mare ridge near the Aitken impact crater. Credit: Smithsonian Institution, University of Maryland. CC BY-NC-ND.

More dynamic

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.

Jaclyn Clark, an assistant research scientist in UMD’s Department of Geology, said: “Many scientists believe that most of the Moon’s geological movements happened two and a half, maybe three billion years ago, 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 modelling 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.

Clark said: “Essentially, the more craters a surface has, the older it is; the surface has more time to accumulate more craters.

“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.”

Small ridges on the Moon’s far side (depicted in yellow) reveal evidence that the Moon may not be as dormant as previously believed. Credit: Tom Watters, Smithsonian Institution. CC BY-NC-ND.

Moonquakes

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.

Clark said: “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.

“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 findings are published in The Planetary Science Journal.