Three tonnes of space junk on a collision course with the moon

Three tonnes of space junk – the leftovers of a rocket – are about to crash into the moon, carving out a massive crater and sending dust flying across the barren, pockmarked surface.

Experts believe the debris will smash into the far side of the moon away from telescopes’ prying eyes on Friday at 9,300km/h (5,800mph). It may take weeks, even months, to confirm the impact through satellite images.

The junk has been tumbling haphazardly through space since China launched it nearly a decade ago, experts believe. But Chinese officials say it is not theirs.

Bill Gray, an asteroid tracker in the United States, said he is confident that it is China’s rocket.

“I’ve become a little bit more cautious of such matters,” he said. “But I really just don’t see any way it could be anything else.”

Scientists expect the object to carve out a hole 10 to 20 metres (33 feet to 66 feet) across the moon.

SpaceX was originally blamed for the upcoming lunar litter after a US-based asteroid tracker identified the collision course in January [File: NASA via AP]

Low-orbiting space junk is relatively easy to track. Objects launching deeper into space are unlikely to hit anything and these far-flung pieces are usually soon forgotten, except by a handful of observers who enjoy playing celestial detective on the side.

SpaceX originally took the rap for the upcoming lunar litter after Gray, who is a mathematician and physicist, identified the collision course in January. He corrected himself a month later, saying the “mystery” object was not a SpaceX Falcon rocket upper stage from the 2015 launch of a deep space climate observatory for NASA.

Gray said it was likely the third stage of a Chinese rocket that sent a test sample capsule to the moon and back in 2014. But Chinese ministry officials said the upper stage had re-entered Earth’s atmosphere and burned up.

But there were two Chinese missions with similar designations — the test flight and 2020′s lunar sample return mission — and US observers believe the two are getting mixed up.

The US Space Command, which tracks lower space junk, confirmed on Tuesday that the Chinese upper stage from the 2014 lunar mission never de-orbited, as previously indicated in its database. But it could not confirm the country of origin for the object about to strike the moon.

Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics supports Gray’s revised assessment, but noted that “the effect will be the same. It’ll leave yet another small crater on the moon”.

The moon already bears countless craters, ranging up to 2,500km (1,550 miles). With little to no real atmosphere, the moon is defenceless against the constant barrage of meteors and asteroids, and the occasional incoming spacecraft, including a few intentionally crashed for science’s sake. With no weather, there is no erosion and so impact craters last forever.

China has a lunar lander on the moon’s far side, but it will be too far away to detect Friday’s impact just north of the equator. NASA’s Lunar Reconnaissance Orbiter will also be out of range. It is unlikely India’s moon-orbiting Chandrayaan-2 will be passing by then, either.

“I had been hoping for something [significant] to hit the moon for a long time. Ideally, it would have hit on the near side of the moon at some point where we could actually see it,” Gray said.

Meanwhile, McDowell says tracking deep space mission leftovers like this is hard.

The moon’s gravity can alter an object’s path during flybys, creating uncertainty. And there is no readily available database, he said, aside from the ones “cobbled together” by himself, Gray and a couple of others.

“We are now in an era where many countries and private companies are putting stuff in deep space, so it’s time to start to keep track of it,” McDowell said. “Right now there’s no one, just a few fans in their spare time.”