In the early hours of Wednesday morning August 5 the upper stage of a Falcon 9 rocket crashed into the Moon in an uncontrolled collision.

No damage was caused, other than the creation of a new crater several metres in diameter, but the event highlights the increasing problem of space junk left in orbit when it has completed its intended purpose.

Natural impacts occur on the Moon daily. On average, Nasa estimates that 33 metric tonnes of meteoroids (space rocks) hit Earth every day, but most of this burns up in the atmosphere before hitting the ground. A smaller proportion make it through and reach the surface as meteorites.

Most of the human-made space debris that falls back to Earth also burns up on its way through the atmosphere. The Moon has no atmosphere, so any debris – either natural or human-made – on a collision course will hit the surface.

First identified and reported as an upcoming collision months ago, the object in this case was the upper stage of the SpaceX Falcon 9 rocket on a mission to ferry two robotic landing craft to the lunar surface. These were Blue Ghost Mission 1, manufactured by Texas-based firm Firefly Aerospace and Hakuto-R, built by the company ispace, which is headquartered in Tokyo, Japan.

The first stage of the rocket did what it was designed to do, took the second – or upper – stage and the payload of spacecraft into low Earth orbit, detached, and returned safely to a landing pad on Earth to be refurbished for reuse.

The upper stage engines then ignited and took the spacecraft on their intended trajectory to the Moon. However, once it had released the spacecraft, its job was complete and it was left in a high elliptical orbit around the Earth.

In a statement, SpaceX said that, for most missions, the company carries out a controlled de-orbit of the Falcon 9 second stage, so that it safely re-enters Earth’s atmosphere........

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