WASHINGTON, July 20 — Early findings suggested something unusual was heading toward the Moon. In January 2022, amateur astronomer Bill Gray noticed that an object designated WE0913A appeared to be on a trajectory that would bring it close to Earth’s natural satellite. Gray, who runs the software tool Project Pluto — used to compute orbital paths for asteroids, comets and artificial satellites — has spent decades tracking space debris.
He maintains a catalog of nearly all rocket bodies in high Earth orbit. When he saw the orbit of WE0913A, he calculated that it would impact the Moon on March 4.
Gray alerted colleagues, including Dr. Jonathan McDowell. McDowell independently verified the calculations. Gray’s work through Project Pluto has long been a quiet backbone of orbital science.
The software computes ephemerides, allowing users to predict where objects in space will be at any given time. For decades, Gray has tracked not only natural objects like asteroids and comets, but also artificial satellites and rocket bodies left in orbit.
His catalog of high Earth orbit rocket bodies is one of the most comprehensive available. When he spotted WE0913A, he did what he has done many times before: computed its future path and realized it was headed for a collision with the Moon. He did not keep the finding to himself.
He reached out to McDowell, who maintains the Jonathan’s Space Report database. McDowell’s independent verification added weight to the prediction. The two astronomers then helped alert the broader scientific community, including NASA.
NASA’s Lunar Reconnaissance Orbiter team planned to use LRO’s cameras to attempt to locate the resulting impact crater after the March 4 event. That effort represented a rare opportunity: observing a fresh crater on the Moon created by a known human-made object.
The impact itself was not directly witnessed, but the prediction allowed scientists to prepare. The collaboration between an amateur astronomer running a software tool from his home and a professional astrophysicist at a major institution illustrates how citizen science is becoming woven into the fabric of space research. Gray later acknowledged errors that had led to an initial misidentification of the object’s origin — but the tracking methodology itself remained sound.
Gray’s willingness to correct his own work reflects the evidence-based approach that defines good science. He did not hide the mistake; he reported it openly.
The reassuring part is that the system of checks and balances worked: Gray’s initial calculation was verified by McDowell, and the prediction held. The error lay in identifying what the object actually was, not in where it was going. In space debris tracking, that distinction is crucial.
The object was a rogue Falcon 9 upper stage, but Gray’s early identification had pointed to a different origin. He corrected the record after further analysis. McDowell’s role extended beyond verification.
His Jonathan’s Space Report database provides a running log of launches, satellites, and debris that feeds into analyses by both professionals and amateurs. When he confirmed Gray’s calculations, the prediction moved from a single amateur’s hunch to a credible forecast.
NASA’s Lunar Reconnaissance Orbiter team then had a target to aim for. The whole chain, from a software tool called Project Pluto to a NASA spacecraft orbiting the Moon, depended on collaboration across institutional boundaries. For those who worry about space debris, here is the hopeful part: the tools exist to track it.
Gray’s catalog of high Earth orbit rocket bodies is not a government database; it is the work of one dedicated amateur. He has been tracking debris for decades, updating his catalog as new objects appear.
The rogue Falcon 9 stage was one object among many, but its Moon-bound path made it stand out. The impact was inevitable once the trajectory was known. The event itself is now history.
What matters going forward is the growing recognition that amateur astronomers can make vital contributions to space situational awareness. The effort to locate the crater will continue, and the data from that search may help refine future impact predictions.
