That’s why I regret to inform you that the Moon is also a horrific deathtrap, and not just because you’ll asphyxiate if you take your helmet off.

The lack of any sort of atmosphere — let alone a breathable one — means that the difference between the daytime and nighttime temperatures on the lunar surface can be hundreds of degrees, so you can be flambéed or frozen. If the Sun gets agitated and throws a maelstrom of electromagnetic radiation your way, there’s no atmosphere or magnetic field to deflect it. And without a gassy shield to impede them, small meteorites (those the size of footballs or pebbles) bombard this desolate realm like bullets. 

That hasn’t stopped America, China and a suite of private spaceflight companies racing to get back to the Moon. They’re going to try and establish a permanent presence on the lunar south pole, home to precious reserves of water-ice — an ancient reserve that can water crops, hydrate astronauts, and be transformed into rocket fuel. And they won’t just have the spaceborne hazards to deal with. They will also, just maybe, have to deal with moonquakes.

With the U.S.’s Artemis lunar program in mind, several recent studies, deploying some clever seismic sleuthing techniques, have tried to better quantify the frequency and intensity of some of these lunar temblors. And they have good news and bad news: powerful quakes could rock the Moon while astronauts are present, but the day-to-day risk of a dangerous shake is low.

“This is not so much an issue for short-duration missions,” says Thomas Watters, a Senior Scientist in the Center for Earth and Planetary Studies of the National Air and Space Museum in Washington D.C., and an author of several recent moonquake studies. The problem, he says, is long-term infrastructure, like parts of a nascent Moon base.

As an example, NASA wants to eventually set up a nuclear reactor on the moon to provide sufficient, sustained power to their operations. “It’s absolutely amazing that they’re talking about that, but damn, I wouldn’t want to put one of those on an active fault,” says Nicholas Schmerr, a planetary seismologist at the University of Maryland and another author on those moonquake studies.

When it comes to quakes, Earth is a bit of a showoff: not only does it produce a staggering variety of them, but it’s also capable of producing more powerful temblors than anywhere else in the inner solar system. 

Thanks to the jostling of its giant tectonic plates, you have faults that throw blocks of land over and under one another, while other rifts cause parts of the crust to scrape against each other. Subduction zones, wherein one tectonic plate gets consumed by the geologic fires below another plate, can produce cataclysmic magnitude 9.0-or-higher events. Even the movement of magma, which smashes through rocks in the crust, can cause the surface world to convulse. 

This seismic activity is ultimately powered by the escape of trapped heat from within the planet’s guts—heat provided by a store of radioactively decaying elements and old embers left behind by Earth’s collisional formation 4.6 billion years ago. The Moon once had plenty of both, but as it’s so tiny, most of this heat leaked into space long ago. Today, the Moon is geologically comatose. There are plenty of faults, like cracks in a desiccated shell. But there are no subduction zones, and (probably) no magmatic serpents slithering below the surface.

Several of the Apollo landings left behind short-lived seismometers on the lunar nearside, and between 1969 and 1977, the often-faint rumblings of something stirring below were picked up. “There are a few different kinds of moonquakes,” says Benjamin Fernando, a planetary geophysicist at the Johns Hopkins Applied Physics Laboratory in Maryland, who was not involved with the recent studies. And each hints at their unearthly origins.

First, you have thermal quakes: the lack of an atmospheric bubble means the lunar surface quickly heats up in the day and rapidly cools at night — meaning the mercury can swing from 250°F to -208°F. The expansion and contraction of rocks during the day-night cycle rocks is enough to cause some shaking.

You also have moonquakes that are our fault — well, our planet’s fault, anyway. “Just like how the Moon raises tides in the oceans on Earth, the Earth raises tides on the Moon. Except the Moon doesn’t have surface water, so the tides are in solid rock,” says Fernando.

Then there are the meteorite impacts. Earth’s thick atmosphere catches and vaporizes small asteroids (read: pebble to house-sized space rocks) all the time without consequence. But the Moon is defenseless, so even relatively petite interlopers can slam into the surface and cause a staggering commotion. “Those impacts come with their own hazard as well,” says Fernando. “So it’s kind of a double whammy, if you like.”

The strongest and most mysterious moonquakes are the shallow ones. “They’re the most dangerous, in some sense,” says Fernando, noting they can reach a magnitude 5.0. And unlike earthquakes, which last for tens of seconds or a few minutes at most, these moonquakes can last for hours, sufficient to potentially knock over any astronaut infrastructure.

There are no working seismometers on the Moon, so Watters, Schmerr and their colleagues have relied on an unusual combination of techniques to better understand these shallow moonquakes. As well as reassessing archival Apollo seismic data, they’ve used NASA’s Lunar Reconnaissance Orbiter (LRO) satellite, which takes photographs of the Moon’s surface, to examine its faults. 

In 2019, their research concluded that several younger faults were activated during the Apollo era in part because the Moon is shrinking. As the last supplies of its internal heat leak out into space, the Moon cools and gradually contracts, triggering shallow quakes on various faults. Earth’s gravitational pull is also responsible for occasionally focusing this lunar contraction, causing specific faults to slip, rather than random ones.

A new study of theirs, published earlier this summer, attempted to work out the frequency of fault-generated moonquakes. They poured through LRO images taken of the undulating Taurus-Littrow Valley, the Apollo 17 landing site. A fault, the Lee-Lincoln schism, can be found there, and its surroundings were explored by astronauts Eugene Cernan and Harrison Schmitt.

Based on the astronaut’s surveying work, and images of the site taken from above by the LRO, Watters and Schmerr reconstructed a potted seismic assessment of the Lee-Lincoln fault. 

Scar marks in the lunar surface next to certain boulders hinted that some may have tumbled downslope after being set loose by moonquakes — with larger boulders requiring higher magnitude events, with greater associated surface shaking, to dislodge them. Evidence of a wider landslide was also plugged into their equations. And the geologic samples brought home by Apollo 17 revealed how long certain boulders had been exposed to mineral-altering cosmic radiation, a proxy for how long those hefty rocks had sat in place.

Their analysis determined that the Lee-Lincoln fault could produce quakes at least as potent as a magnitude 3.0—and that larger quakes were possible in the area. 

“The same class of faults also occur in the south pole area,” says Watters. Last year, another of their studies identified several such faults located close to, and within, some of the areas NASA has identified as candidate landing regions for Artemis III, which will land American astronauts somewhere in region later this decade. “It’s not a seismically benign area.”

The team estimate that a magnitude 3.0 moonquake on the Lee-Lincoln fault happens once every 5.6 million years. Any astronauts sojourning on the lunar surface for a matter of weeks, then, are very unlikely to be smothered by a quake-induced landslide.

Their base infrastructure, however, is more vulnerable. Should they experience a stronger moonquake while there, anything tall and relatively thin — say, the 165-feet-high Starship Human Landing System that SpaceX wants to send to the Moon — might be at risk of being felled, or at the very least dangerously shaken up.

This sort of remote seismic detective work is valuable, says Fernando, as it helps scientists put some limits on the frequency and intensity of moonquakes. But it can only tell you so much. “You’re only seeing the aftermath of a seismic event,” he says. Our understanding of moonquakes is still patchy, and there’s only so much you can do from Apollo-era seismic data and orbital imagery. 

Fortunately, that’s soon to be rectified: the Artemis III mission will bring a cutting-edge moonquake detector to the lunar south pole. The Lunar Environment Monitoring Station, or LEMS, consists of two seismometers: one will be placed into a borehole, while the other will be put into a ditch. Both will listen out for the Moon’s geologic grumbles for at least three months, but likely many years.

Not only will LEMS help scientists better understand the seismic hazard to humanity’s lunar wayfarers, but it’ll also illuminate the region’s bizarre underworld. Billions of years ago, a ginormous asteroid smashed into the lunar south pole with a preternatural force. “It excavated all the way down into the lowermost portion of the crust, maybe even into the mantle,” says Schmerr, the LEMS deputy principal investigator. Scientists would love to explore the scar tissue – one of the largest impact basins in the solar system — that’s still visible today.

NASA also plans to launch the Farside Seismic Suite, a robotically deployed seismometer, to the Moon’s Schrödinger basin in 2027. China is also proposing to add its own seismometer to an upcoming robotic lunar mission. It’s the making of a proper seismic network — one allowing scientists to listen to the drumbeat of the Moon, and particularly the south pole, the site of what is to become humanity’s first outpost on another world.

But until that moonquake monitoring system is operational, our lunar sleuths have some advice for the Artemis program. “Make sure you’re not setting up long-lived infrastructure near active faults,” says Schmerr. 

“They’re all over the place,” says Watters. If you’re going to set up a Moon base, “locate the fault, then get at least [10 miles] away from it.”