On March 4, a spent four-metric-ton rocket stage will end its uncontrolled 7.5-year journey through space on a high note: it will slam into the far side of the moon, near the 570-kilometer-wide Hertzsprung crater, about 9,300 kilometers per hour, creating its own modest crater. Earth is no stranger to space junk falling from the sky, most of which burns up in the atmosphere or crashes into the ocean. But the idea that a significant portion of humanity’s trash will litter the moon has sparked concern around the world.
So how should we all feel about this impending impact? Should we throw up our hands in despair at humanity’s recklessness or, at the very least, gesticulate wildly while speaking our grievances? Like many of his colleagues, John Crassidis, a space debris expert at the University at Buffalo, chooses to shrug his shoulders instead. “It doesn’t matter,” he said.
First and foremost, the disappearance of this rocket isn’t going to disrupt Earth’s alabaster orb. As confirmed by its cratered surface, our natural satellite can throw off all sorts of substantial blows. “Don’t worry, the moon will still be there afterwards,” says Crassidis.
But what about the scattering of unsightly waste on our immaculate lunar partner? It turns out that this rocket will join many other piles of space junk already strewn across the lunar surface. “This rocket, right now, I don’t think is a big deal,” says Alice Gorman, a space archaeologist at Flinders University in Australia. The precedents show that we should not worry, not yet, anyway.
The only legitimate concern for this impending impact is what exactly it portends for our future. The United States, China, Russia and others increasingly see the Moon as humanity’s first extraterrestrial outpost. “The hope is that we will come back to stay,” says Vishnu Reddy, co-head of the Space Situational Awareness Laboratory at the University of Arizona. “And you don’t want stuff raining down on people if they live there.”
See you later, Crater
The rocket stage’s lunar collision course was revealed in January, largely thanks to the work of Bill Gray, an astronomer behind Project Pluto, a popular series of programs used to track nearby moving objects of the earth. How the rocket got there in the first place, however, is a little less clear. Gray originally identified it as belonging to SpaceX, a holdover from the 2015 launch that put the National Oceanic and Atmospheric Administration’s Deep Space Climate Observatory satellite into space.
But it was apparently a mistake of identity. Gray’s later re-examination of the rocket stage’s trajectory and timing strongly suggests that it probably belongs to China: it is likely a rocket booster used in the 2014 launch of the Chang’e 5-T1 mission, a trial for China’s Chang’e 5 sample-return mission to the moon that was launched in 2020. Other astronomers agree with Gray’s revised conclusion, while like Reddy and his students at the University of Arizona, who telescopically observed the object to identify its various features, which resemble those you would find on a Chinese space rocket.
Perhaps another twist will reveal that the rocket belongs to another nation or company; maybe not. Either way, “we trust Newton’s laws,” says Harvard-Smithsonian astronomer Jonathan McDowell Astrophysics Center. Regardless of its origins, the object will still hit the moon on March 4.
When it does, it will join a long list of predecessors. “There are loads of things that have crashed into the moon in the past,” Gorman says. The Apollo landings are perhaps the most famous lunar adventures, but humanity’s first-ever direct contact with the moon was far less graceful: the Soviet Union intentionally slammed Luna 2, an unmanned space probe filled with propaganda pennants, in 1959.
Since then, the moon has been subjected to all kinds of artificial impacts. During the Apollo era, parts of several Saturn 5 rockets were deliberately launched at it to generate moonquakes detectable by seismic experiments placed there by astronauts. In 2009, a NASA mission specifically designed to film the moon did just that: the Lunar Crater Observation and Detection Satellite, or LCROSS, dropped its exhausted rocket into the moon’s south pole, blasting into the space a plume of rock and water ice that scientists have studied from in the distance.
It’s not just rocket parts that call the moon their final resting place. Several whole spacecraft also have lunar graves. Some are intentional: in recent years, a few of Japan’s and NASA’s probes have, after completing their missions, been directed to crash into the Moon. Others are accidental: Israel’s Beresheet spacecraft was supposed to land on the moon in 2019, but malfunctions caused it to crater unceremoniously instead.
Despite this long history of lunar pounding, some parts of the moon are more expensive – and therefore more vulnerable – than others. What if, say, an errant piece of space junk crashed into Apollo 11The Tranquility Base landing site, where humans first stepped onto another world? Fortunately, the odds of such an event are astronomically slim, and this latest impactor is unlikely to eradicate a piece of space history: it will descend to the lunar far side, where virtually no surface exploration is n took place.
While this distant impact is good news for space history, it’s far from ideal for scientists who might otherwise hope to telescopically spy on it and its LCROSS-like plume. And ground observers aren’t the only ones who don’t have a ringside seat: there won’t be any scientific instruments near the likely crash site that could record data during the collision. At some point, NASA’s Lunar Reconnaissance Orbiter (LRO) will fly overhead in search of a telltale crater, but even that won’t produce many, if any, meaningful reveals.
A shower of rockets
That leaves – for those still scrambling for reasons to care – nothing but worry about what this event means for lunar exploration in the years and decades to come. For one thing, the back and forth on the identity of the rocket stage “highlights the absence of a comprehensive lunar debris tracking system,” Gorman said.
Astronomers like Gray do most of the detective work on this rather than a government agency like the US Space Force, which tracks objects in Earth’s orbital domain. That’s because debris that goes beyond the range of Earth’s geostationary satellites isn’t a major concern for most nations right now. “Once it gets over 50,000 miles, the Space Force interest level starts to drop. By the time it hits 100,000, it’s about zero,” McDowell says.
This lack of interest is partly due to the difficulty of tracking debris in deep space. “It’s really difficult,” Reddy says, whether you’re using radar or optical tracking methods. “Objects are further away, they are smaller, they are fainter. You have to worry about this great reflector called the moon. That’s not a problem right now, he adds, “but in the next eight to ten years we’ll probably be on the order of at least 50 [lunar] missions.” Several space probes will be in orbit, as could astronauts, cosmonauts and taikonauts, either aboard spacecraft bound for the lunar surface, or perhaps even residing in a space station such as the lunar gateway proposed by NASA.
Eventually, there will be enough man-made wreckage around or near the moon for two objects to crash into each other. Last October, India’s Chandrayaan-2 orbiter had to avoid NASA’s LRO. “We are doing maneuvers in low Earth orbit all the time. You’d think we wouldn’t have to do one around the moon,” says Crassidis.
The impending proliferation of lunar-orbiting missions means the moon’s surface is also set to become more crowded, with various proposals for moon bases, science outposts and mining sites. Unfortunately, “the airless moon cannot shield itself from incoming debris like Earth does, where most objects burn up upon re-entry,” says Hannah Sargeant, a planetary scientist at the University of Central Florida. The odds will remain low for long, but it’s possible that one day a piece of falling space junk could flatten a lunar explorer. And even if all falling waste misses vulnerable surface sites, assets in orbit could suffer a deadly backfire: pebbles and dust thrown into space from such impacts could potentially break off or even punch holes in various spacecraft. “It’s like launching a suborbital missile: lunar pebbles like lunar ASATs [antisatellite weapons]says McDowell.
With all that in mind, “it makes sense for us to keep tabs on where’s what,” Reddy says, not to address a problem that exists now, but to mitigate one that may exist in the future. Reddy and his colleagues at the University of Arizona are already hard at work: They just received $7.5 million from the US Air Force to create and maintain a catalog of near-lunar objects and provide support in dodging the debris to the upcoming missions. This prototypical framework, Reddy says, is something “that the military can take on at some point when it becomes a bigger issue.”
It will be a long time, however, before the moon’s space junk problem begins to approach the tragedy unfolding in our planet’s orbital realm. “Even in a few decades, I think it won’t be as bad as the problem of space debris in low Earth orbit,” McDowell said. None of this means that we should dismiss the problem itself, because who wants to transport Earth’s problems to the Moon?
“It might behoove us to say, ‘Okay, this time we’re going to think a little more about the future,'” Gray says.