A spent SpaceX Falcon 9 upper stage is due to hit the Moon on Aug. 5, and scientists say the dust it throws up might be visible from Earth.
The stage is left over from the Jan. 15, 2025 launch that carried Firefly’s Blue Ghost-1 lander to the Moon. The same flight also carried Resilience, the Hakuto-R Mission 2 lander built by Japan’s ispace. Both payloads went on their way. The stage did not.
Where it lands, and what might be seen
The impact is expected near the Einstein and Bell craters, close to the western lunar limb. That location matters, because it may put the event within reach of ground-based and space-based instruments.
An international team has posted a study on arXiv saying the plume could briefly be bright enough to see against the dark sky near the Moon’s edge. Moongazers with sufficiently sensitive telescopes might catch it.
William Jo, a graduate research assistant at the University of Texas at Austin, and his colleagues ran physics simulations of the crash. They predict the central ejecta spike will climb to roughly 47 to 62 miles (75 to 100 kilometers) in altitude.
“Our calculations suggest the plume should be several orders of magnitude brighter than the dark-sky background for the first few minutes after impact,” Jo told Space.com. He added a warning. “This is a single nominal case. The real one will look different, and the numbers are on the optimistic side.”
Jo’s bigger worry is that observers will watch for the flash and miss the rest. “Most observers will stop at the sub-second flash and never track down the ejecta, which is the part that should actually be visible, and where the science is,” he said.
Why researchers care
A used rocket stage is a hollow, spacecraft-like body, and Jo notes there are very few impact models for human-made objects like it. They seem to produce very different plumes than asteroids or comets do. Watching this one, he said, offers “a rare chance to open up ejecta-plume science and calibrate those models against a real event.”
Separate research led by Benjamin Fernando of Los Alamos National Laboratory in New Mexico calls the flash and plume “potentially observable” from ground and space. Fernando and his co-authors say many properties of the event, visual magnitude among them, are imprecisely predicted for now.
They list other uses for the crash: testing a pipeline for locating impacts on the lunar surface for future seismic experiments, studying dust and plume behavior, and weighing the hazard that debris from artificial impacts could pose to astronauts on the surface. In their modeling, the maximum ballistic range of resolved particles falls slightly under 1,000 km. That is far enough, the study says, to matter for future astronauts or infrastructure across much of the lunar surface.
NASA’s Lunar Reconnaissance Orbiter will pass over the projected crash site about seven days before the impact and again about seven days after. Brent Garry, an LRO project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said the second pass should help. “After the impact we might have a little bit more knowledge of where it is. We can do some additional targeting about a week after the impact.”
