A discarded SpaceX Falcon 9 upper stage is on a collision course with the moon, and skywatchers may be wondering whether they'll be able to witness the rare event firsthand when it slams into the lunar surface early Wednesday morning (Aug. 5).
The 45-foot-long (13.8-meter), 8,000-pound (4,000-kilogram) rocket stage, left over from the January 2025 launch of Firefly Aerospace's Blue Ghost and ispace's Hakuto-R lunar missions, is expected to strike the moon at about 2:35 a.m. EDT (0635 UTC) on Aug. 5. Traveling at roughly 5,400 mph (8,700 km/h), the impact will occur near the moon's western limb, close to Einstein Crater on the moon's Earth-facing side.
While the collision itself is unlikely to be visible from Earth, observers may have a chance to spot what's known as an ejecta plume rising above the lunar surface. Depending on the force of the impact, debris could be blasted high enough above the moon to stand out against the blackness of space, making it briefly visible to observers on Earth, according to Project Pluto. "Maybe we'll see the flash. Maybe we'll see rocks ejected from the crater. Maybe we'll even see both," astronomer Bill Gray, who first identified the rocket stage's eventual lunar collision, wrote on his Project Pluto website.
The rocket is expected to strike a sunlit portion of the moon near its edge as seen from Earth. Any flash from the impact itself is expected to be washed out by the bright lunar surface.
However, material blasted high above the lunar horizon could briefly become visible against the darkness of space, creating a faint plume that advanced amateur astronomers may be able to capture with sufficiently large telescopes and cameras. Recent simulations suggest the central ejecta plume could climb as high as 60 miles (100 kilometers), though whether it will be detectable from Earth remains uncertain.
Even if conditions cooperate, viewing won't be ideal for much of North America. At the time of impact, the moon will sit only about 40 degrees above the southeastern horizon for observers along the U.S. East Coast, giving skywatchers a relatively low viewing angle before dawn. Observers in parts of South America may have more favorable viewing conditions, with the moon higher in the sky during the event, according to Project Pluto.
Regardless of whether the impact can be seen from Earth, several spacecraft will be watching from much closer vantage points.
South Korea's Danuri lunar orbiter is expected to observe the impact in real time, offering a unique view from lunar orbit. Meanwhile, NASA's Lunar Reconnaissance Orbiter (LRO) will photograph the impact site before and after the collision, allowing researchers to measure the newly formed crater and compare it with other human-made impacts on the moon.
Whether or not the ejecta plume is spotted from Earth, researchers say the accidental crash represents a valuable scientific opportunity. Unlike natural meteoroids, the hollow aluminum rocket stage will strike the moon with well-known size, mass and velocity, giving scientists a rare chance to test models of how impacts excavate lunar material and create craters.
The observations could also help researchers better understand the hazards posed by space debris as both crewed and robotic missions to the moon become increasingly common, if all goes according to plan.
