Advanced dating methods have allowed tracking changes in the far side of the Moon, revealing evidence that it is geologically active.
Evidence from the lunar seas (dark, flat areas of the Moon filled with solidified lava) suggests that the Moon experienced significant compression in its distant past.
Researchers suspected that the large arched ridges on the near side of the moon were formed by contractions that occurred billions of years ago, concluding that the lunar sea has remained inactive since then.
However, a new study reveals that what lies beneath the lunar surface may be more dynamic than previously thought.
Two scientists from the Smithsonian Institution and a geologist from the University of Maryland discovered that the small ridges located on the far side of the Moon were significantly younger than those previously studied on the near side. Their findings were published in The Planetary Science Journal.
The Moon is geologically active
“Many scientists believe that most of the geological movements on the Moon occurred two and a half or perhaps three billion years ago,” said Jaclyn Clark, an assistant researcher in the Department of Geology at the University of Maryland, in a statement.
“But we are seeing that these formations have been geologically active recently in the last billion years and may still be active today. These small lunar ridges appear to have formed in the last approximately 200 million years, which is relatively recent considering the time scale.”
Using advanced mapping and modeling techniques, the team found 266 small ridges previously unknown on the far side of the Moon. The ridges generally appear 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 environment.
Tectonic activity in the last 160 million years
“Basically, the more craters a surface has, the older it is; the surface has had more time to accumulate craters,” explained Clark. “After counting the craters around these small ridges and seeing that some of them intersect existing impact craters, we believe that these formations have been tectonically active in the last 160 million years.”
Interestingly, Clark noted that the ridges on the far side were structurally similar to those found on the near side of the Moon, suggesting that both were created by the same forces, likely a combination of gradual contraction of the Moon and changes in the lunar orbit.
Apollo missions detected shallow lunar earthquakes decades ago; the new findings suggest that these small ridges could be related to similar seismic activity. Learning more about the evolution of the lunar surface could have important implications for the logistics of future missions to the Moon.
“We hope that future lunar missions include tools such as a ground-penetrating radar so that researchers can better understand the structures beneath the lunar surface,” said Clark. “Knowing that the Moon is still geologically dynamic has very real implications for where we plan to locate our astronauts, equipment, and infrastructure on the Moon.”
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