A high-definition image of the Mars Australe lava plain on the Moon taken by Japan’s Kaguya lunar orbiter in November 2007. Credit: JAXA/NHK
Last month, astronomers reported that a discarded upper stage of a Falcon 9 rocket, launched 7 years ago, was on a collision course with the Moon. The rocket in question carried
This animation features actual satellite images of the far side of the moon, illuminated by the sun, as it crosses between the DSCOVR spacecraft’s Earth Polychromatic Imaging Camera (EPIC) and telescope, and the Earth – one million miles away. These images were captured on July 16, 2015. Credit: NASA/NOAA
“Essentially,” he wrote, “I had pretty good circumstantial evidence for the identification, but nothing conclusive. That was not at all unusual. Identifications of high-flying space junk often require a bit of detective work, and sometimes, we never do figure out the ID for a bit of space junk; there are a couple of unidentified bits of junk out there. (At least, not identified yet.)”
But the detective work he’d carried out was suggestive enough that he considered it a positive ID for the SpaceX rocket, and no one questioned it. That is, until February 12, 2022, when Gray received an email from Jon Giorgini at the Jet Propulsion Laboratory (
This isn’t the first time an artificial object has hit the Moon. This photo shows the impact site of Apollo 16’s S-IVB Booster, taken by the Lunar Reconnaissance Orbiter in 2015. Credit: NASA/Goddard/Arizona State University
The whole affair is somewhat trivial in the grand scheme of things, but it does raise some interesting questions about how space junk beyond low Earth orbit is tracked, and whether better tools are needed to do so.
In low Earth orbit, space junk is monitored carefully, as the region is much more crowded, and precise tracking is required to avoid collisions. This is especially important in and around the International Space Station, where space junk could pose a threat to astronauts. But in deep space, there is very little official tracking of objects – most of the attention here is focused on asteroid-hunting to ensure that we are aware of any possible threats to Earth. Human-made objects in deep space are not systematically tracked. Gray himself only does so part-time.
As humans venture back to the Moon in the coming decade, Gray suggests that it might be prudent to implement a more rigorous tracking system, and outlined a few steps to take to get started.
First, he suggests that launch providers ought to make the last known trajectories of their boosters publicly available. Second, they should put some consideration into reducing space junk, deorbiting used boosters where possible. And finally, Gray suggests that in the long run, an international (and well-funded) organization will probably be required to effectively carry out precise object tracking.
Oh, and if you’re wondering where the DSCOVR booster actually is – well, for now, no one knows. Gray’s best guess is that it’s somewhere in orbit around the Sun. Without active controls to keep it at the L1 Lagrange point, it will have likely floated away to find its own path through the Solar System.
If you want to see Gray’s description of the whole affair in his own words, you can read it here.
