Lunar terrain reveals recent geological activity on the moon

The moon’s unwavering illumination of the night sky has been a source of wonder and inspiration for thousands of years. Since the first satellite images of Earth’s surface were taken in the 1960s, our understanding of our planet’s companions has evolved significantly over time. The lunar surface is a complex interplay of cosmic interactions and planetary systems, presenting a vast array of landforms that testify to its history.

One such feature is the lunatic scarp, a long (<10 km) curvilinear landform produced by thrust faulting in which older rocks are pushed over younger units, causing crustal shortening. These are thought to be among the youngest landforms on the Moon, having formed within the last approximately 700 million years (the Copernican lunar geological time scale). For context, this is considered "young" geologically, as the age of the universe is estimated to be 13.7 billion years.

These crescent scarps are the focus of new research, published in Earth and Planetary Science Lettersuses craters in the surrounding highland landscape as indicators of scarp movements and is therefore an ideal candidate for age estimation.

Explaining the significance of their research, Dr. Jaclyn Clark of the University of Maryland said: “Unlike Earth, the Moon does not have plate tectonics, which has prompted many scientists to explore what drives tectonic movements on the Moon and other rocky bodies in the solar system.

“The presence of these small leaf-like thrust faults suggests that the Moon’s surface is shrinking due to long-term cooling of the Moon’s interior (at a much faster rate than Earth’s).

“By exploring crater clusters, we can better understand when tectonic activity occurs and how seismic energy attenuates away from faults through regolith (the loose rock and dust on top of bedrock), which can help plan safer lunar missions.”

Dr. Clark and colleagues used crater size-frequency distribution measurements to determine the age of 34 lobe scarps on the lunar surface. They further combined this with previous research to produce a data set of 60 lobe scarps on the near and far sides of the moon. In addition, the data provide information on the intensity of seismicity associated with scarp movement and the potential for fault reactivation.

To this end, scientists input high-resolution satellite images taken by the Lunar Reconnaissance Orbiter camera into the geological mapping software ArcGIS to measure the size and frequency of craters in a specific area to calculate cumulative crater density and age models.

The team looked at age distribution patterns between the footwall (units of rock below the fault) and hanging wall (units above the fault that push up) in the crater near and far from the cliff. Proximally, about 38% of the footwalls are younger than the adjacent hanging wall, 47% are the opposite age, and 15% are about the same age. For the distal scarp, 33% of hanging walls were more than twice as old as the proximal hanging wall, whereas the distal footwall was generally not much older than the proximal footwall.

Dr Clark explained: “When we first started making crater size frequency distribution measurements at proximal locations in the hanging wall and footwall, we initially found that the hanging wall region was produced at a younger age than the footwall region, which led us to It is believed that there may be greater earthquake shaking in the hanging wall.

“Extending this method to 34 scarps, we found that this was not true for all scarps. The hanging wall and footwall of many scarps had similar ages (i.e., the ages overlapped within the margin of error). Most of the differences in ages were in proximal and distal locations, which is most likely due to attenuation of seismic energy away from the fault.

Therefore, this demonstrates that shocks caused by lobe scarp motions decrease with distance and typically affect the upper 1 km of the crust. This means that seismic activity is restricted to shallower depths, increasing the intensity of shaking at the surface compared with deeper parts of the Earth’s crust; it may also have a larger impact because the Moon’s weaker gravity makes it more susceptible to small-magnitude earthquakes. The impact of higher vibration intensity of earthquakes.

Additionally, the team found that lobe scarp ages are randomly distributed in space, with no specific region of the planetary body showing a similar set of ages, and no clear correlation between age and scarp length. However, they did find some correlation between scarp shape and age, with linear scarps forming 250 million years ago and arcuate and irregular scarps forming in the past 50-150 million years.

Therefore, this suggests that the scarps formed due to a combination of millions of years of cooling of the Moon’s interior, resulting in global contraction (producing arcuate and irregular scarps) and diurnal tidal stresses (linear scarps).

Most thrust faulting activity associated with lobe scarp formation dates back to the past 400 million years, with the most recent being 24 million years ago. Interestingly, scientists have also noticed that over the past 250 million years, the size of craters affected by scarp motion has been declining, thus indicating that moonquake activity has also decreased during this time. Dr. Clark noted that “this may mean that the rate of internal cooling is slowing down,” but more research is needed to determine whether this trend will continue.

Overall, scarp motion promotes the formation of new craters, reshaping the moon’s landscape and making its terrain younger. The impact of the reset of crater chronology on our understanding of lunar processes is something scientists are keen to explore further, as Dr Clark explains, “Since there is no atmosphere on the Moon, processes such as tectonism and volcanism are much less likely to occur. changed the lunar surface.

“Due to the limited number of samples from the Moon, crater size frequency distribution measurements are currently our best option for determining surface age. In addition to obtaining surface ages, exploring the crater size range can provide insights into how craters behave in certain materials. degradation.

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