The moon may have formed in as few as five hours after the cataclysmic collision between Earth and a long-lost protoplanet, new simulations suggest. The surprising findings could help shed light on other historic impacts throughout our cosmic neighborhood and beyond.

Experts strongly suspect that the moon was created when a Mars-size space rock called Theia smashed into an early version of our planet, back when the solar system was young and extremely unstable. This colossal impact likely would have turned the once-neighboring worlds into spinning clumps of molten rock that eventually coalesced and cooled into the versions of Earth and the moon we see today. Without this collision, which also may have left chunks of Theia buried deep within our planet, many scientists think that life may have never existed on Earth.

Lunar rocks collected during NASA's Apollo missions have provided evidence to support this theory, dubbed the giant impact hypothesis. These samples also tell us that the moon is around 4.5 billion years old, meaning the collision occurred roughly 100 million years after the sun was born. But although scientists have previously simulated the impact event, it has been tricky to ascertain exactly how the moon formed and how long it took to emerge after the Earth-Theia collision.

In the new study, published Sept. 1 in The Astrophysical Journal Letters, researchers conducted a series of simulations focusing on the varying potential geological properties of both Earth and Theia prior to their collision. This factor has been relatively understudied until now.

"When you simulate the Earth and the moon as colliding bodies with [different] geologic properties, it changes how the moon forms out of that impact — that's something we considered unnecessary before," study first author Adeene Denton, a geologist and planetary scientist at the Southwest Research Institute in Boulder, Colorado, said in a statement.

Until now, simulations of the Earth-Theia impact have focused mainly on the masses of the colliding neighbors. But in the new study, the researchers were most interested in the material strength of the two bodies, particularly the hardness of their exteriors.

"Models have evolved to include material strength, something that's really important when you're studying collisions between smaller bodies like asteroids," Denton said. "We weren't sure if it would matter for the moon or not. When we did the simulations, we found it actually matters quite a bit."

The main factor in the strength of colliding bodies is temperature. Both Earth and Theia were very young when they smashed together, so they were still hot and had soft or molten surfaces. These properties would have cushioned the collision, allowing the debris to stay largely intact and enabling the moon to form more quickly. But when the giant impact hypothesis was first proposed (in 2001), researchers initially thought the collision occurred much later, meaning that the bodies would have cooled and become more brittle. In this case, their collision would have created a larger field of rocky debris that would have taken longer to coalesce.

Researchers simulated the collision using a range of potential temperatures and found that under the most extreme scenario — where the pair were at their hottest — the moon could have formed in just five hours. However, this is just one potential outcome, and there is no way of knowing exactly how hot — and, therefore, how strong — Earth and Theia really were when they smashed together.

When the moon took shape, it was initially covered with a magma ocean that took hundreds of millions of years to solidify. Even then, its increased proximity to Earth meant that it was likely a volcanic hellscape. However, over time, it moved away from our planet, cooling further, and it is now assumed to be geologically dead. (The moon is continuing to slowly move away from us and could eventually escape our planet's gravity entirely, if the dying sun doesn’t destroy it and us first in around 5 billion years.)

The new simulations highlight the importance of material strength in planetary impact modeling, which could change what we know about other ancient collisions, like the one that knocked Jupiter's moon Ganymede off its axis or the one that birthed Saturn's moon Titan.

Additionally, the findings could have implications in the search for exomoons — the hypothetical moons of distant exoplanets, which have so far remained elusive, according to Live Science's sister site Space.com. Until now, one of the main ways astronomers have been hunting for these alien satellites is by looking for debris fields around exoplanets. However, if the moon is anything to go by, these debris fields could be very short-lived and difficult to identify.

The moon could have formed in a matter of hours following the giant impact between Earth and a Mars-size protoplanet early in the history of the solar system. The theory comes from new simulations that take into account how the internal temperature of young protoplanets affected their geologic properties and therefore the collisions they experienced.

This giant impact scenario has become the leading theory of how the moon formed, thanks in particular to work done by planetary scientist Robin Canup. Since 2001, she has conducted and refined numerous computer simulations that describe how a Mars-size body called Theia collided at an angle just right to throw debris into orbit around the proto-Earth.

Now other researchers are getting in on the act. Adeene Denton of the South-west Research Institute led a team who performed some of the most detailed simulations of the collision yet, taking into account more of the geologic properties of the colliding worlds.

"Models have evolved to include material strength, something that's really important when you're studying collisions between smaller bodies like asteroids or for my previous paper about the formation of the Pluto–Charon system," said Denton in a statement. "We weren't sure it would matter for the moon or not. When we did the simulations, we found it actually matters quite a bit."

It turns out that warmer bodies are weaker than colder ones. After the planets formed, they were still hot inside from their formation, which would have affected their material strength. Given that the moon-forming impact occurred not long after the solar system's formation, this would have affected the collision with Theia — but to what degree depends on exactly when the collision occurred and how much Theia had cooled.

As Theia smashed into Earth, it was utterly destroyed. While much of what was left of Theia's shattered iron core sank into the Earth, a large ring of debris wrapped around Earth to form the moon.

The main effect of the temperature being warmer in the outer few hundred miles of Theia was that it would have affected its ability to deform upon impact and absorb the momentum of the collision. This, in turn, would have affected how debris was strewn around Earth to form the moon. Therefore, by including varying temperatures and material strengths in the simulations, Denton's team was able to get a better look at how the collision and the resulting formation of our moon played out.

Previous simulations have shown two possible scenarios. One is that the ring of debris hung around for a substantial amount of time, allowing the moon to accrete from it gradually. The other scenario, first depicted in NASA-led simulations in 2022, implies that the moon came together from this debris in a matter of hours.

Now, Denton's models potentially bolster this startling possibility.

If Theia was colder, meaning that the impact occurred a little later in the history of the solar system, perhaps 100 to 150 million years after the birth of the planets, then the ring of debris would have formed in such a way as to allow the moon to accrete gradually. And because it was stronger, more of Theia would have survived intact to merge with Earth.

On the other hand, a warmer Theia that impacted Earth less than 60 million years after the planets' formation, would create a scenario where the moon could form very quickly while Theia itself would be obliterated.

"Depending on how hot the Earth and Theia are prior to the collision, the impact can destroy Theia and produce this massive disk of debris that eventually forms the moon," said Denton. "But when I used the same parameters as original impact modeling – down to the equal temperature structures inside both bodies — within around five hours, an intact moon emerged."

That would have been quite a day in the history of our planet, acquiring a new moon and an almighty headache all at once.

"These surprising and exciting new results imply a potential connection between the physical properties of the moon today, including perhaps its volatile content, and the thermal state of the Earth and Theia at the time of the giant impact," said the Southwest Research Institute's Robin Canup, who was not involved in this study. "This in turn might help scientists better constrain when the moon-forming event occurred."

In both scenarios, the moon appears to be made mostly from Theia's mantle material, with just a little bit of Earth's mantle mixed in. This latter finding is surprising, given the similarities between the moon's composition and Earth's mantle. However, research has shown that there's clearly more to the story because despite the similarities there are also some puzzling differences in the levels of isotopes that cannot be easily explained by current simulations, including Denton's.

The simulations could have repercussions in the search for exomoons. If the moon did form in a matter of hours, then searching for exomoon-forming disks around terrestrial exoplanets might be a fruitless endeavor because such disks would be so short-lived. Moon-forming disks around gas giant exoplanets would be a different matter, however, because those disks do not form from impacts, but rather from material leftover from assembling those planets.

The results were published on Sept. 1 in The Astrophysical Journal Letters.

As usual, SpaceX is dreaming big.

The company plans to build factories on the moon, using robots to do much of the heavy lifting, Elon Musk said on Tuesday (Aug. 4) during SpaceX's first-ever quarterly earnings call.

"We are going to land a lot of tonnage on the moon," he said. "We're going to build the factories on the moon. The robots will be helpful with that."

This is not a newly revealed vision; Musk first laid it out in February, in a blog post that announced SpaceX's purchase of xAI, a company that the billionaire entrepreneur founded in 2023. But Musk doubled down on it this week, showing investors that off-Earth manufacturing is very much front-of-mind for SpaceX.

The factories in question will build SpaceX's Starmind AI satellites, if all goes according to plan. The company aims to operate a million-strong Starmind constellation in Earth orbit in the coming years, and then go farther afield with the craft after that.

Eventually, SpaceX wants to launch locally made Starmind satellites off the lunar surface using electromagnetic mass drivers — basically, extremely powerful rail guns.

"Using robots on the moon to scale up manufacturing on the moon — which, I know it sounds, like, super sci-fi right now, but it's going to happen — will enable us to build the mass accelerator on the moon," Musk said.

"And if you have a mass accelerator on the moon, and you have solar and radiator production on the moon, you can — I know this sounds totally nuts — but you can you can probably scale to 1,000 times the economy of Earth in terms of intelligence launched to space, but probably, you know, maybe even a million times," he added.

"Solar and radiator production" refers to the manufacture of key Starmind satellite components: solar panels to power them and radiators to dump the large amounts of heat they'll produce into the vacuum of space.

Musk didn't provide details about the robotic lunar labor force. But he's presumably counting on Optimus, a humanoid robot built by another one of his companies, the carmaker Tesla. Musk has previously said that SpaceX will launch some Optimus units to Mars in the near future, to help pave the way for human settlement of the Red Planet.

Those robots will fly on Starship, SpaceX's fully reusable next-gen megarocket, which is currently gearing up for its 14th test flight. Indeed, Starship is key to most of the company's plan's both in Earth orbit and beyond.

"Starship aims to quadruple payload capacity and reduce launch costs by 10 times compared to our Falcon 9 rocket, unlocking significant capabilities across all of our business segments," SpaceX Chief Financial Officer Bret Johnsen said during Tuesday's earnings call.

"We continue to make progress building the infrastructure required to support thousands of Starship launches per year, including accelerating Raptor and launch vehicle production, the buildout of our gigabays, and making significant progress towards activating multiple launch pads at Starbase and in Cape Canaveral at Pad 39A and Pad 37," he added. (Raptor is the engine that powers Starship, and Starbase is SpaceX's South Texas site, which serves as the current hub of Starship manufacturing, testing and launch activities.)

Tuesday's call was a landmark for SpaceX — its first as a publicly traded company. Musk founded SpaceX as a private concern in March 2022 and took it public this past June, via the richest IPO in history.

The IPO raised $86 billion and valued SpaceX at $1.77 trillion. Only six American companies had higher market capitalizations at the time — NVIDIA, Apple, Alphabet (Google), Microsoft, Amazon and the semiconductor manufacturer Broadcom. (Market caps fluctuate all the time, going up and down with companies' stock prices.)

The main point of Tuesday's call was to discuss SpaceX's first-ever earnings report, which covered the second quarter of this year. The company's revenue over that stretch was $7.8 billion, a 92% increase over the same period in 2025, according to the report. SpaceX lost more money than it made during Q2 2026, but the shortfall was considerably smaller than in Q2 2025 — $541 million versus $1.0 billion.

The final resting place of SpaceX's moon-smashing rocket has been found.

The Korea Pathfinder Lunar Orbiter, known as Danuri, has captured imagery of the crater blasted out by the Falcon 9 upper stage that slammed into the moon early on Wednesday morning (Aug. 5).

"Danuri began observations about 30 minutes before the collision and, through orbit control, passed over the impact site multiple times, conducting a total of 8 imaging sessions," officials with the Korea Aerospace Research Institute (KARI) said via X this morning (Aug. 6). "Through this observation, changes in the terrain around the impact site and traces of ejecta spread were confirmed."

"Danuri secured both pre-collision and immediate post-collision footage, enabling analysis of changes caused solely by the collision and providing important research data," they added in the X post, which shared several before-and-after images of the impact site.

The Falcon 9 in question launched on Jan. 15, 2025, sending two private robotic moon landers — Firefly Aerospace's Blue Ghost and ispace's Resilience — to a high, moon-crossing Earth orbit. The duo then made their own way to the moon; Blue Ghost landed successfully on March 2 of that year, but Resilience crashed during its touchdown attempt.

The Falcon 9's first stage came back to Earth shortly after liftoff for recovery and reuse, as such boosters commonly do. Falcon 9 upper stages, by contrast, are expendable. SpaceX usually disposes of them in Earth's atmosphere, but the upper stage on the Blue Ghost-Resilience mission used almost all of its fuel getting its payloads to their distant destination. So the 8,800-pound (4,000 kilograms) rocket body remained up there, orbiting Earth — until solar activity and gravitational forces pushed it on a collision course for the moon.

That collision occurred at 2:34 a.m. EDT (0634 GMT) on Wednesday, according to KARI officials — right in line with predictions. Scientists calculated some other parameters ahead of time as well. For example, the rocket body probably hit the moon at about 5,400 mph (8,690 kph), gouging out a crater up to 89 feet (27 meters) wide.

The new observations by Danuri, as well as future work by other lunar probes, will help verify such predictions.

"The observation data secured by Danuri will be linked with follow-up observations from NASA's Lunar Reconnaissance Orbiter (LRO) and utilized in international collaborative research," KARI officials said in the X post.

It may be that some ground-based telescopes caught the impact as well. Astronomers at the Instituto de Astrofísica de Andalucía in Spain believe they captured a video of ejected material blasting off of the lunar surface around the predicted time of impact:

The Falcon 9 upper stage wasn't the first rocket body to slam into the moon. The third stage of a Chinese Long March 3C crashed into the lunar surface on March 4, 2022, for example. And the third stage of NASA's Saturn V rocket gouged out craters during multiple Apollo moon missions.

Danuri is South Korea's first lunar probe. The spacecraft launched on Aug. 4, 2022 atop a Falcon 9 and began circling the moon four months later. It carries six payloads, five of them provided by Korean universities and research organizations. The sixth is a NASA instrument called ShadowCam, which hunts for signs of water ice in permanently shadowed regions at the lunar poles.

A spent rocket body hitting the moon made headlines this week, but the reality is that the unplanned collision by a SpaceX upper stage was just the latest in a long history of human-made objects meeting their end by impacting the lunar surface.

Astronomers around the world kept their telescopes trained on the moon early Wednesday morning (Aug. 5), when the rocket stage from a January 2025 U.S. commercial lunar landing mission was calculated to strike the celestial body. Though the fate of the SpaceX Falcon 9 part was unintentional — solar activity and gravitational forces caused the stage to slam into the moon — the impact offered a rare opportunity to try to observe the flash from the impact and the plume of lunar material it sent flying.

By noon (EDT) on Wednesday, there were no confirmed reports of the impact being caught on film, but a telescope in Chile spotted the debris plume, according to the Associated Press.

"This rare occurrence has decades of history, going back to the Apollo era," wrote Jared Isaacman, NASA's administrator, in a post to his social media accounts. "The reality is that meteoroids strike the lunar surface hourly, with impacts comparable to this upper stage occurring roughly every six days."

Inventorying the impacts

The moon is peppered with the scattered metal remains of missions that missed their mark, came down too quickly or were purposefully sent careening into the regolith to learn more about the makeup of Earth's natural satellite.

In fact, the very first mission to successfully fly by the moon was intended to be an impactor. The former Soviet Union's Luna 1 probe was designed to hit the moon but instead zoomed past its target and entered orbit around the sun on Jan. 2, 1959.

Luna 2, launched nine months later, became humanity's first object to reach the lunar surface, purposefully slamming into Sinus Lunicus ("Bay of Lunik"), along the southeastern edge of Mare Imbrium, on Sept. 14, 1959.

The U.S. followed suit, though not as NASA intended, with the Ranger 4 probe impacting the far side of the moon on April 26, 1962. The mission had included an impactor, but both it and its lander failed to operate due to a failure to deploy the spacecraft's solar arrays.

Once humans began arriving on the moon with NASA's Apollo program, scientists found another reason to direct spent rocket and spacecraft stages into a collision course with the surface. Beginning with Apollo 11 in 1969 and concluding with Apollo 16 in 1972, seismometers were placed on the moon to measure natural "moonquakes" and the effects on the moon when the missions' Saturn SIV-B stages and Apollo lunar module descent stages made hard landings.

The data collected helped geologists learn more about the interior makeup of the moon, including that a rocky mantle exists under the outer crust.

After Apollo, planned impacts (and missions) slowed down, if not outright stopped, but the SpaceX collision on Wednesday was not the first in more than 50 years. Between 1993 and today, 11 probes — four from China, three from Japan, two from the U.S. and one each from India and the European Space Agency (ESA) — were intentionally deorbited at the end of the end of their missions around the moon.

Some of these impacts were performed to discard the craft, but others — like Lunar Prospector, LCROSS and Chandrayaan-1 — helped confirm the presence of water by examining the resulting plume.

Unintentional collisions are fewer in number, as are rocket stages, but are not unprecedented. A rocket body that hit the moon's far side in March 2022, leaving behind a small double crater, was later identified as a Long March 3C rocket that launched China's Chang'e 5-T1 mission around the moon in 2014.

Litter versus liability

Without a large human population on the moon, the risk that these planned and unplanned impacts present at current is minimal. But the concern rises as NASA and other world space agencies, as well as commercial interests, begin to increase the pace on establishing their now-planned sustainable facilities for astronauts to live and work on the lunar surface.

"The future lunar base will incorporate reusable spacecraft that not only deliver astronauts and payloads, but also become part of the infrastructure itself," Isaacman said in his post, referring to how reuse can be a way to reduce the number of vehicles needed to be discarded of on the moon.

The Artemis Accords, an internationally agreed-upon set of standards led by NASA and currently signed onto by 70 countries, also includes a provision for its members that spacecraft and their associated rocket components must be disposed of safely.

Early this morning, a SpaceX rocket slammed into the moon at seven times the speed of sound. Now, lunar orbiters are trying to get a look at the aftermath.

This morning (Aug. 5) at about 2:35 a.m. EDT (0635 GMT), the upper stage of a SpaceX Falcon 9 rocket crashed into the moon. To dissect what exactly happened, scientists are looking for imagery of the crash site, with the help of a couple of moon probes.

"NASA’s Lunar Reconnaissance Orbiter and NASA’s ShadowCam instrument on the Korea Pathfinder Lunar Orbiter will look for opportunities to capture before‑and‑after imagery of the impact site," NASA spokesperson Rob Garner, of NASA's Goddard Space Flight Center in Maryland, told Space.com. "Image availability depends on several factors, including the impact location, lighting conditions, and when each spacecraft’s orbit next carries it over the area, which may take a few days to receive any imagery."

While you've likely seen the first stages of Falcon 9 rockets gracefully land back on Earth for reuse, the rocket's 9,000-pound (4,000 kilograms) upper stage is disposable. Typically, it's sent to burn up in our atmosphere after its missions are over.

However, that wasn't possible with this rocket, which launched two private lunar landers — Firefly Aerospace's Blue Ghost and Tokyo-based ispace's Resilience — to a high, moon-crossing Earth orbit in January 2025. The Falcon 9 upper stage used most of its fuel getting to this distant location and couldn't make it back to deorbit in Earth's atmosphere.

So the company performed a different maneuver to take care of this upper stage, Julianna Scheiman, director of NASA science and Dragon programs at SpaceX, said during a press conference on Aug. 3.

"For high-energy missions, we need to perform a different maneuver to ensure the second stage itself is safe per the appropriate rules and regulations, and so we did that here," she said.

But the rocket body was still subject to natural forces, which acted on it over time.

"What has happened is, essentially, a mixture of solar activity and gravity forces have put it on a path towards the moon," Scheiman said.

The Falcon 9 upper stage ended up slamming into the moon this morning at about 5,400 mph (8,690 kph). It likely blasted out a crater up to 89 feet (27 meters) wide, according to scientists' calculations.

This was certainly not the original intended outcome for this rocket. But it presents an opportunity for researchers, who plan to take advantage of it to learn more about the moon.

"NASA’s Meteoroid Environments Office will attempt to image the impact around the predicted time using ground‑based telescopes at the agency's Marshall Space Flight Center in Huntsville [Alabama]," Garner added. "Because the impact flash and plume are expected to be faint, the chance of seeing anything from Earth remains low, and local weather can affect observations as well. Any data collected will help scientists better understand impacts from artificial objects and the potential effects on future lunar exploration."

Today's impact took place on the sunlit side of the moon, the brightness of which made observations difficult for skywatchers hoping to watch the crash from afar with telescopes. But the two lunar orbiters might be able to see not just the crash and impact crater but also the plume of dust kicked up by the rocket's death dive.

So far, observations from Earth have revealed some information. Scientists at the Lowell Observatory in Flagstaff, Arizona reported detections of a lunar plume from the impact.

"We can safely say that we measured a response from the rocket stage impact as a sodium and lithium gas plume a few 10’s of kilometers in size lasting between 5 and 10 minutes after impact," Carl Schmidt told Inside Outer Space's Leonard David.

Such images of the event would provide "an opportunity to test pipelines for measuring flash properties to locate impact events seismically, and to better understand the multi-modal hazards posed to future lunar infrastructure and astronauts from space debris impacting the moon," researchers led by Benjamin Fernando of Los Alamos National Laboratory in New Mexico wrote in a recent paper discussing the then-upcoming event.

So hold tight, as researchers are now eagerly collecting and analyzing the images captured by these orbiters, and we might get images of the rocket crash, the lunar plumes and remaining aftermath soon.

An abandoned part of a SpaceX Falcon 9 rocket is projected to crash into the moon at 2:35 a.m. EDT on Aug. 5 — and two new studies suggest the event may be visible in telescopes from parts of North and South America, providing both amateur and professional astronomers with a rare, real-time viewing opportunity. Both studies are available as preprints on the arXiv server.

The impending Aug. 5 impactor is the truck-sized spent upper stage of a Falcon 9 rocket. In 2005, the rocket boosted two privately owned landers into orbit around the moon, before leaving its upper stage in an elliptical orbit around Earth, according to OrbitalRadar.com.

A report earlier this year estimated that the collision would occur near the moon's Einstein crater, with the rocket grinding into the lunar surface at a speed of 5,436 mph (8,748 km/h). Although that sounds fast, it's about six times slower than a natural impactor, like an asteroid, would hit.

What can you see with a telescope?

The initial impact flash of the collision — which will last less than a second and be hidden on the sunlit side of the moon — will likely be invisible to casual skywatchers, according to one of the new studies. The brightest estimates for the impact put it at 20 times dimmer than Saturn. The resulting crater likely won't be visible from Earth, as the study estimates that the hole is relatively small and shallow ‪—‬ about 90 feet (27 meters) wide and up to 16 feet (5 m) deep.

More promising for Earthbound skywatchers is the plume of regolith (and potentially water vapor) the impact will loft. The plume will likely reach several miles in height, with computer-based simulations from the second study showing it may tower up to 31 miles (50 km) high. This will make it visible over the moon's limb as a cloud, with the debris spreading up to 112 miles (180 km) from the impact site.

The plume will hang above the lunar surface much longer than the flash ‪—‬ for up to 400 seconds, or close to seven minutes; during this time, it will scatter sunlight toward Earth. Even then, the plume will be too faint to be observed with the naked eye, William Jo, a graduate research assistant at the University of Texas at Austin and co-author of the second study, told Live Science in an email. Viewers will need a good backyard telescope to see it.

"Where the science is"

Although the event will be dim and occur on the sunlit portion of the moon, skywatchers are gearing up to watch it. Benjamin Fernando, a postdoctoral researcher at Los Alamos National Laboratory and co-author of the first study, told Live Science in an email that there "will be an observing campaign involving professional and amateur astronomers from around the world."

In particular, he said, folks in South America and continental North America — where it will be night, with the moon high above the horizon — will have the best chance of seeing it, although you will need at least a 4-inch (10 centimeters) telescope.

However, Jo was less optimistic. "I don't think it would be an easy task for an amateur astronomer," he said, but if they know exactly where to point their telescope and tackle atmospheric refraction, they might see the plume. Nonetheless, he urged well-equipped observers to try observing the plume, as that is "where the science is."

This science, Jo said, would help researchers understand how everything delivered to or disposed of on the moon will ultimately affect the lunar surface. "This would be useful for studying disposal methods for upper stages, maybe how far ejecta will travel, and whether or not the ejecta will hit sensitive instruments, or in the far future lunar bases," he added.

Previous collisions of human-made objects on the moon have likewise led to some major scientific insights. For example, the 2009 crash of a Centaur rocket's upper stage was analyzed by NASA's Lunar Crater Observation and Sensing Satellite mission, which revealed subsurface ice near the lunar south pole. As a result, the lunar south pole is now considered the most coveted location for moon missions that aim to establish a permanent human presence on Earth's satellite.

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