How moonquakes could rattle Artemis astronauts

More than 3 billion years ago, when the Moon’s volcanic mare (the dark lunar “seas”) were formed, the Moon was rife with tectonic activity and moonquakes that shook its surface. Evidence of these ground-shuddering events can be seen on the Moon’s nearside in the form of long features called wrinkle ridges — created when sheets of basalt lava slumped and settled toward the depressed middle of the basin cradling the maria.

But while the Moon no longer hosts active volcanoes, it may still be more geologically active than it appears. In the past several years, studies of mare surfaces have identified a new type of feature dubbed small mare ridges, or SMRs, which appear to have formed recently, implying that small-scale tectonic activity may continue on the Moon today.

In the January 2025 issue of The Planetary Science Journal, a team of researchers at the Smithsonian Institution in Washington, D.C., and the University of Maryland in College Park present the most comprehensive survey yet of small mare ridges, examining them on both the near and far sides of the Moon. Their results provide evidence of ongoing modern tectonic activity that could impact upcoming lunar missions.

Current moonquakes

SMRs are thought to be formed in part by the global stresses of the ongoing contraction of the Moon: As the Moon’s interior cools, the world very slowly shrinks — amounting to roughly 150 feet (50 meters) over the last several hundred million years. The tides created by the changing effect of Earth’s gravity throughout the Moon’s tilted and elliptical orbit and late-stage mare cooling are also thought to play a role in forming SMRs.

The recently discovered ridges are typically 330 feet (100 meters) wide and up to 3,300 feet (1,000 meters) in length, too small to be seen from Earth. But using the richly detailed images from NASA’s Lunar Reconnaissance Orbiter, researchers have identified 1,120 SMRs on the nearside. Their fresh appearance implies they formed within the past billion years, and they appear across the face of the Moon.

The new work expands the study of SMRs to the lunar farside to provide a more complete picture of modern lunar tectonic activity. The farside possesses fewer maria than the nearside. Indeed, only two, Mare Engenii and Mare Moscovionese, have been officially named. The massive South Pole-Aitkin Basin, covering most of the farside southern hemisphere, contains many small mare patches that allowed expanding SMR studies to the farside.

Because the farside crust is thicker, the volcanic eruptions that created its mare patches occurred later than the formation of the classic nearside maria. Curiously, the farside maria are devoid of the lengthy wrinkle ridges common to the nearside. This may be due to the farside’s thicker crust, which is less flexible than the nearside crust and did not slump under the weight of basalt lying on it.

A valuable resource

For their SMR investigations, the team of researchers (Cole Nypaver and Thomas Waters of the Smithsonian and Jaclyn Clark of the University of Maryland) used a publicly available portal to access high-resolution imagery and terrain data gathered from millions of laser altimeter shots fired at the Moon from NASA’s Lunar Reconnaissance Orbiter.

A total of 266 farside SMRs were identified, mostly in the southern hemisphere. This is about a quarter of the number of identified nearside SMRs, but a good sampling considering there are far fewer basalt patches of the far side.

To determine the ages of the SMRs, the researchers used a couple of methods. In one method, they examined the Lunar Reconnaissance Orbiter imagery to count craters near the features. Fewer craters indicate a younger surface, as less time has passed for meteoroid impacts to accumulate.

In another method, the team studied small craters that have been bisected by an SMR. Small craters have a shorter lifespan than larger ones because they are more quickly filled with regolith thrown from surrounding impacts. Thus, finding a small crater bisected by an SMR indicates the ridge is geologically young.

Within the South Pole-Aitkin Basin and Bolyai and Aitken craters, the team found 13, 20, and 32 small craters, respectively, bisected by an SMR. By comparing the anticipated lifetime of the small craters at these three locations, they calculated that the SMRs intersecting the craters formed 110, 14, and 34 million years ago. A derived age of millions of years may seem ancient, but on the lunar timescale of 4.6 billion years, the formation of these SMRs is an astonishingly recent event and demonstrates the Moon may still be seismically active.

Moonquakes and spacecraft

The potential of present-day moonquakes in the south polar region has stark implications for the crewed Artemis landings planned in the near future. An occasional small murmur of a moonquake will be a scientific treat, allowing seismic instruments delivered by Artemis to study the geologic structure of the lunar interior. However, a lunar “Big One” could damage the infrastructure of a lunar science base. Cracks in walls that would be mere annoyances after a terrestrial earthquake would have much more ominous consequences in the unforgiving vacuum environment of the Moon.

The moonquake resilience of the SpaceX Starship Human Landing System also becomes paramount if lunar tectonic activity is still present and periodically quivers the south pole. The crew cabin of the monument-like Starship will tower more than 110 feet (33 meters) above the surface. As depicted in current illustrations, the small landing gear footprint offers little stability from the seismic roll of a large moonquake. A toppled Starship spells doom for the crew.

If moonquakes are a frequent reality, a more robust redesigned Starship HLS landing gear will be heavier but reduce the payload carried to the Moon. It would also impact plans to deliver science cargo and large rovers to the lunar south pole.

The smaller Blue Origin Blue Moon lunar lander is shorter than the Starship HLS and its landing gear has a proportionally broader and more stable footprint. However, the development of the Blue Moon lander is several years behind Starship HLS and the Blue Moon cargo capacity is significantly less than that projected for Starship.

Previous seismic studies 50 years ago by the Apollo Lunar Seismic Experiment indicated moonquakes are shallow events correlated to the location of lobate scarps — another type of terrain with tectonic origins. These scarps, typically about 130 feet (40 meters) high, form when the Moon’s interior cools and shrinks, leaving the more brittle crust with little support. The crust eventually snaps, part of it riding up and over another part. The morphology of SMRs is similar to the larger lobate scarps and points to their also being a source of regional lunar seismic activity.

Zone of avoidance

One conclusion from the study of SMRs is that these regions should be avoided by future crewed landings until the stability of these regions is fully understood. Nypaver and his colleagues suggest that instead of deploying seismic instruments near SMRs on crewed Artemis missions, these regions should be thoroughly studied by uncrewed landers flown by international partners or the NASA Commercial Lunar Payload Services program.

An intriguing point about the discovery of widespread small mare ridges is that the portal used in the research, the web-based LROC Quickmap tool, is available to every lunar enthusiast. Click on the Quickmap link and zoom in on your favorite regions of the Moon and explore its intricate detail and structure. Who knows? You too might discover something new about the Moon.