A few weeks ago, news of a SpaceX rocket stage that was going to hit the Moon spread like wildfire. Now, the astronomer tracking it has announced quite the twist: The rocket is definitely hitting the Moon, but it is not the SpaceX one. It’s likely the stage of a Chinese rocket.
The story is a great example of how science should ideally work, self-correcting when more information becomes available. It is also a very deep look at how complicated tracking space junk is, and that mistakes are not only possible but likely. The rocket is not the SpaceX one that carried the DSCOVER satellite to its special position of Lagrangian point 1, but is actually the booster of the Chang'e 5-T1 lunar mission, the precursor to the Chinese sample return mission.
Bill Gray of astronomy software company Project Pluto has tracked this piece of space junk for years, ever since it was detected by the Catalina Sky Survey about a month after the DSCOVER launch.
At first, the piece of junk was considered a small asteroid – but it then became clear, by how it reflected light, that it was actually human-made.
Given the limited information from the launch, Gray and others looked at potential candidates for this orbital find. The SpaceX rocket was a very good and close guess – but good and close is not always right.
Gray received an email from Jon Giorgini, a senior engineer at NASA’s Jet Propulsion Laboratory, who spotted a mistake in the original statement which suggested that DSCOVER went past the Moon, but that wasn’t the case. Gray had to go back to his email archive back to 7 years ago to work out why he identified the object as the SpaceX rocket.
“I did that digging in full confidence it would prove that the object was, in fact, the DSCOVR second stage,” Gray wrote in a blog post.
He looked at the data and showed that while there was good circumstantial evidence that it was the right guess, there were some oddities. The email prompted a deeper look into the nature of the object, and Gray found a better and more plausible candidate in the Chinese rocket.
“In a sense, this remains 'circumstantial' evidence,” Gray added. “But I would regard it as fairly convincing evidence. So I am persuaded that the object about to hit the moon on 2022 Mar 4 at 12:25 UTC is actually the Chang'e 5-T1 rocket stage.”
There is not a tracking mechanism for these objects, so it is often down to the work of amateur astronomers to keep track of these pieces of space junk.