The rocket booster slammed into the moon.
This is something we know a lot about. It gets weird as soon as you start reading the story.
Bill Gray, a software designer who wrote Guide, is the central figure in this saga. As the events happened, he wrote about it.
On March 14, 2015, the Catalina Sky Survey found an object in the sky that looked like an asteroid. It was initially thought to be an asteroid and given the temporary designation WE0913A, but after being identified as a piece of space junk, it was assumed to be a rocket booster.
It was assumed that this object was the upper stage of the F9 rocket, since it was found to have passed by the Moon just two days after the launch. Gray has an updated version of his page with more information.
The Chang'e 5-T1 was launched in October of last year and was intended to test atmospheric re-entry of a capsule sent to the moon. It used a three-stage Long March 3C rocket and some students at the University of Arizona were able to show that the third stage of the rocket was much better than the second stage.
The Chinese government claimed that the booster burned up in the atmosphere in a safe way. Gray is very confident that the 5-T1 booster is the one that was being discussed.
On May 22, the LRO took pictures of the region, which was predicted to be impacted on March 4, 2022. The story took a turn when it found a new impact in the correct place.
A crater about 28 meters across is created by the overlap of the two craters. For comparison, a tennis court is about 24 meters in length.
A single object hitting the moon usually leaves a single crater. There are many double craters that are likely due to either a single asteroid breaking up before impact or a pair of asteroids hitting each other.
Dozens of human-made objects, including rocket boosters, have hit the Moon, and many have been seen, but the craters left are not as large as they could be.
Why did this thing do that? It is still a mystery. A booster is a long tube with very heavy rocket engines and nozzles at one end. The tanks are not very heavy once the fuel is used. Most of the force of impact and crater carving comes from the engines, and I think the rest of the booster might modify that crater at best.
I wasn't sure if the rocket came in at a low angle. The top of the booster hitting first could create one crater, then the engines hitting 10 or so meters downrangecarving out the second, but Gray notes that the impact angle was only 15 off vertical, so that can't be explained. If the booster was still attached to the top, there would be two craters since it would have a heavy mass at each end.
It is not known why there are two craters. The craters can be seen in the LRO images, but their characteristics are hard to tease out. When the lunar surface is rough and irregular, it can affect the shape and structure of craters.
Due to the mystery and sleuthing involved, this is an interesting story, but also important. NASA, China, and other space agencies are ramping up their exploration of the Moon, and as more material is sent there, more space junk and more impacts are likely. Governments and companies need to make sure their cast-off debris doesn't pose a threat to other lunar missions, because these objects have to be tracked better, predicted better, and in general. It needs to be taken very seriously that space traffic is a very big deal.
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