🌑 Discovering Small Mare Ridges: Signs of Active Lunar Geology
The Moon, long thought to be a geologically inactive world since its volcanic past ended billions of years ago, is revealing surprising evidence of recent dynamism. In a groundbreaking study published in late 2025, planetary scientists at the Smithsonian Institution's National Air and Space Museum mapped thousands of subtle features known as small mare ridges (SMRs), low, winding ridges crisscrossing the Moon's dark basaltic plains called maria. These maria formed from ancient lava flows during the Moon's volcanic era, covering about 17% of the lunar surface, primarily on the near side.
Using high-resolution images from NASA's Lunar Reconnaissance Orbiter (LRO) camera, researchers identified 1,114 previously unrecognized SMR segments across the nearside maria, bringing the total catalog to 2,634. These ridges, often just a few meters high and transitioning seamlessly from prominent cliffs in the highlands, indicate compressional tectonics driven by the Moon's ongoing contraction. Unlike Earth's plate tectonics, which recycle crust through subduction and seafloor spreading, the Moon's rigid, single-plate lithosphere experiences global stress from cooling, leading to thrust faults where one crustal block overrides another.
This discovery completes a global picture of lunar tectonism. Previously, lobate scarps—steep, arcuate cliffs tens of meters high—were known mainly in the lighter highlands, but SMRs fill in the maria gaps, showing uniform shrinkage effects. Their average age of 124 million years, determined by crater counting (where fewer craters mean younger surfaces), aligns closely with lobate scarps at 105 million years, placing both within the last billion years or roughly the final 20% of the Moon's 4.5-billion-year history.
- SMRs are subtler than lobate scarps due to the smoother maria terrain.
- They often connect directly to highland scarps, proving shared fault origins.
- Widespread distribution suggests contraction affects the entire globe, not just poles or equator.
The Science Behind Lunar Contraction
The Moon's shrinkage stems from its cooling interior. Formed from debris after a Mars-sized impactor struck early Earth about 4.5 billion years ago, the Moon started molten. As it cooled over eons, the core and mantle contracted, pulling the surface inward by an estimated 50 to 100 meters globally in recent geological time. This desiccated the interior, reducing volume without significant melting today.
Stress builds until faults rupture, thrusting older crust over newer along shallow thrust faults, typically 1-10 km deep. On Earth, such features occur in convergent zones like the Himalayas, but lunar versions are smaller due to lower gravity (one-sixth Earth's) and no water to lubricate faults. NASA's earlier analyses confirmed this via LRO imagery of fresh scarps and boulder tracks, evidence of recent slips.
Quantitatively, models show the Moon has wrinkled like a drying prune, with radial contraction patterns. This process continues today, albeit slowly at millimeters per year, powered by residual heat loss. For context, Mercury shrank far more dramatically, forming giant scarps kilometers high.
🌕 Moonquakes: Echoes of Apollo and Modern Insights
Moonquakes, seismic events on the lunar surface, were first detected by the Apollo Passive Seismic Experiment (PSE) instruments deployed from 1969-1972 on Apollo 11, 12, 14, 15, and 16. Over 12,000 events were recorded, categorized into deep moonquakes (20-700 km depth, tidal-triggered by Earth), shallow moonquakes (20-100 km, up to magnitude 5.5, tectonically driven), and thermal moonquakes (from sun-shadow temperature swings cracking regolith).
Recent reanalysis of Apollo data links shallow moonquakes to thrust faults. Eight of 28 shallow events occurred near scarps during lunar apogee (farthest from Earth), when tidal pull peaks, with odds against coincidence under 4%. Fresh boulder fields and landslides on scarps, visible in LRO images, suggest quakes as recent as thousands of years ago.
SMRs now expand quake-prone zones into maria, previously considered stable. Magnitudes rarely exceed 5—weak by Earth standards but potent on the Moon due to brittle regolith and low gravity, potentially triggering regolith avalanches lasting hours.
- Deep: Frequent, weak, tidal.
- Shallow: Rare, strong, fault-related.
- Thermal: Common, superficial.
- Meteoroid impacts: Variable.
Risks and Revelations for Artemis Lunar Missions
NASA's Artemis program aims to land humans near the lunar south pole by 2026-2028, targeting water ice in shadowed craters for fuel and life support. However, studies reveal young faults in candidate sites like de Gerlache Rim 2 and Nobile Rim 1, where modeled quakes could shake ground up to 0.2g acceleration, risking landslides in loose regolith slopes.
For short missions, risks are low, but long-term bases face cumulative hazards: structural fatigue, habitat shifts, or resource site collapses. Seismic monitoring via instruments like the Farside Seismic Suite is planned. SMRs remind planners that no region is quake-free.NASA's south pole fault study urges site vetting.
Positive note: Quakes probe the interior, revealing core size and composition, vital for science goals.
Advancing Planetary Science Through Research
This revelation fuels academic interest in planetary geology. Universities worldwide study lunar samples and data, training experts for missions. Careers abound in analyzing tectonics, from modeling faults to deploying seismometers. Explore research jobs or professor jobs in higher education to contribute.Smithsonian's press release highlights team efforts like Cole Nypaver and Tom Watters.
Future missions like Artemis will deploy new sensors, generating data for PhD theses and grants. Actionable advice: Aspiring scientists, master GIS for LRO imagery, learn Fortran for Apollo data reprocessing, and network via conferences.
Photo by Yuvraj Singh Parmar on Unsplash
Navigating the Moon's Living Landscape
Recent tectonic activity underscores the Moon's vibrancy, with SMRs and scarps signaling contraction and quake potential. This informs safe Artemis landings, inspires planetary research, and excites exploration. For insights on professors teaching lunar science, visit Rate My Professor. Pursue space-related higher ed jobs, career tips at higher ed career advice, or university jobs. Share views below and stay informed on cosmic frontiers.