A steady stream of space missions litter the Moon’s surface with hardware buried in its regolith. A recent impact site also left a distinctive and interesting scar, creating two impact craters of equal size. Scientists who studied the collision believe that there may have been an undisclosed object that hit the Moon and whose origin is still a mystery.
On March 4, 2022, a runaway rocket booster crashed into the surface of the Moon. It was believed to be a SpaceX Falcon 9 rocket released into high orbit in 2015, but later investigations revealed that it was actually a booster that China launched as part of its lunar exploration program in 2014. However, the thruster’s impact created two craters on the Moon’s surface instead of one, perpetuating this space mystery and causing scientists to question what exactly hit the Moon that day.
A group of researchers from the University of Arizona had been tracking the object’s orbit and location of hitting the Moon for seven years before this impact. The researchers described their analysis of the rocket’s light reflection signature and movement through space in a paper published in The Planetary Science Journal. Based on the observed characteristics, the researchers suggest that it was indeed a thruster from China’s Chang’e 5-T1 mission, but that it also carried a mysterious payload that vanished on the lunar surface.
“This is the first time we’re seeing a double crater,” Tanner Campbell, a doctoral student at the University of Arizona and lead author of the new study, said in a statement. “In the case of Chang’e 5 T1, the impact was almost straight down and to get these two craters of approximately the same size,” he said in a statement. “We know you need two separate, roughly equal masses.”
The research team was observing the sky to detect and study asteroids when they noticed an object speeding through the space between the Earth and the Moon. Initially the identity of the object was unknown and so it was named WE0913A. As noted, it was initially incorrectly identified as a Falcon 9 rocket booster, but was later confirmed to belong to China’s Long March 3C rocket, which was launched for a future sample return mission test flight. The purpose of this thruster was to place its payload into the designated lunar orbit, and after its work was completed it remained in space.
The researchers used a high-power telescope to observe the thruster and measured changes in the incident light reflection. This helped them track its movement as it progressed in orbit. However, the pusher’s behavior was quite strange. “It was something that happened in space as long as it was exposed to the gravity of the Earth and the Moon and the light from the Sun,” Campbell said in a statement. “So, specifically, the rocket body is a big, empty shell with a heavy engine on one side.” When you think about it, you expect it to shake a little. But it was spinning very consistently end-to-end.”
This led the researchers to believe that there was something else mounted on the front of the thruster that acted as a counterweight to the two engines that served to keep it stable in orbit.
After the object hit the Moon, researchers also observed two impact craters, providing further evidence for their theory. “Obviously we have no idea what this could be,” Campbell said. “Maybe it’s an extra support structure, additional instrumentation or something else,” he said. “We’ll probably never know.”
China generally keeps details of its missions secret, so it’s no surprise that the thruster was carrying a mysterious object and the Chinese space agency has not disclosed the nature of that object. But as more missions to the Moon are planned, it would probably be right for various space agencies and industry leaders to offer more transparency about the objects they want to place on the Moon.
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