At precisely 6.35am GMT on a Wednesday morning, a piece of a SpaceX rocket — roughly as tall as a five-storey building and weighing four tonnes — slammed into the Moon at 8,690 kilometres per hour. Nobody on Earth saw it happen with their own eyes. But a telescope in the Chilean desert caught something almost more remarkable than the crash itself.

The European Southern Observatory's Very Large Telescope, perched high in the Atacama, detected glowing "spectral lines" in the plume of dust that billowed up from the impact. These colourful streaks were the chemical fingerprints of sodium and lithium gas, visible for between five and ten minutes. The plume itself stretched across a few tens of kilometres — not bad for something that nobody planned. Carl Schmidt, an astronomer at Boston University's Center for Space Physics, led the analysis.

He was careful to manage expectations. "This observation did not go perfectly and this is a very crude analysis, but I wanted to share something quickly, and we can say more about these results in time," he said. Here is where it gets genuinely strange. The sodium is thought to have come from the lunar soil itself, disturbed by the violence of the impact.

The lithium, however, may have originated from the rocket stage — meaning the Moon is now quietly holding a trace of human-made chemistry in its dust.