3-ton rocket almost certainly just smashed into the moon at 5,771 mph

After at least seven years hurtling through space, a 3- ton (2.7 metric tons) discarded rocket stage has probably smashed into the moon today (March 4) at a blistering 5,771 mph (9,288 km/h). 

The discarded rocket stage was projected to land at Hertzsprung crater on the moon's far side at 7:25 a.m. EST (1225 GMT), with the energy from the collision punching out a crater which scientists believe could be up to 66 feet (20 meters) wide. The impact likely sent a plume of lunar dust hundreds of miles high. 

This is the first time that space junk has accidentally collided with the lunar surface, according to scientists. But because the collision occurred on the moon's far side, it could take scientists months to find the crater, confirm the impact and possibly find clues that could put its controversial origins to rest.

Related: 5 strange, cool things we've recently learned about the moon

Many experts think that the junk, which has been hurtling around space for more than seven years, is the spent upper stage of a rocket launched during one of China's first forays to the moon, in 2014. But Chinese officials disagree, claiming that their upper stage burned up in Earth's atmosphere years ago, Live Science previously reported. Before this, it was thought that the rocket belonged to SpaceX. 

Bill Gray, a U.S. astronomer and the developer of the asteroid-tracking software Project Pluto, said he is confident that the "moon crasher" is China's rocket.

"I'm fairly convinced that there's no way it can be anything else," Gray told Live Science. "At this point, we rarely get anything quite this certain."

Gray first predicted that the debris would collide with the moon after it was spotted tumbling through space in March 2015. The object (which had been given the temporary name WE0913A) was picked up by the Catalina Sky Survey, an array of telescopes in Arizona that scans the sky for dangerous asteroids that could smash into Earth. But WE0913A wasn't orbiting the sun like an asteroid would. It was orbiting Earth, leading Gray to suspect that the object was human-made. 

After initially misidentifying the object as a SpaceX Falcon 9 rocket, Gray went back to the data to find another spacecraft fitted very closely with the trajectory of the moon-bound debris: the upper stage of China's Chang'e 5-T1 mission, which launched in October 2014 as part of a preliminary mission to send a test capsule to the moon and back. 

Chinese foreign ministry officials deny that the space junk is theirs, insisting that the Chang'e 5 rocket already burned up on re-entry to Earth's atmosphere. But U.S. experts believe that Chinese officials could be mixing up the 2014 rocket with the rocket from a 2020 mission and that the former is whatt hit the moon Friday. Further evidence came Tuesday (March 1), when the U.S. Department of Defense's Space Command, which tracks low-Earth orbit space junk, released a statement confirming that China's 2014 rocket never deorbited.

Gray believes his orbital data, which is a near-perfect match to the Chinese rocket’s initial trajectory, is conclusive.

"It's on the orbit that an awful lot of lunar missions take; its inclination means that, in the past, it was headed out over China; it was going east in the way Chinese lunar missions do; and its estimated launch time falls within 20 minutes of the Chang'e 5-T1 rocket," Gray said.

An amateur radio satellite was attached to the Chang'e 5-T1 for the first 19 days of its flight, Gray said, and the trajectory data sent back from that satellite matches the rocket debris' current trajectory perfectly. Others have also found important clues, with the Jet Propulsion Laboratory's Center for Near Earth Object Studies confirming Gray's analysis of the orbital data and a University of Arizona team identifying the rocket as part of the Chang'e 5-T1 mission from the spectrum of the light being reflected by its paint.

As the space junk hit the moon's equator on its far side, the impact will go unobserved from Earth for some time until satellites orbiting the moon, such as NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan-2 spacecraft, find themselves in the right orbit to look down upon the crater. It could take many months for scientists to spot the new lunar hole, but scientists are hoping the images could help them better understand the moon's subsurface contents, as well as how it will deform when hit by an object with a known speed and mass.

Given the speed that the rocket is traveling, it's likely that little evidence of it will remain besides the crater it has made. At the instant the rocket strikes the moon, a shock wave will travel through the impactor in mere milliseconds, shattering it into shards of exploding metal.

Although this is the first piece of space junk to unintentionally collide with the moon, it isn't the first time a human-made satellite has crashed there. In 2009, NASA's Lunar Crater Observation and Sensing Satellite was intentionally fired into the moon's south pole at 5,600 mph (9,000 km/h), unleashing a plume that enabled scientists to detect the chemical signatures of water ice. NASA also disposed of the Apollo programme Saturn V rockets by firing them into the moon.

Gray said the confusion surrounding the object's identity highlights a real need for space-faring countries and companies everywhere to better track the rockets they send into deep space — not just so they aren't mistaken for Earth-threatening asteroids but also to keep the space around Earth clean from debris.

"From my selfish standpoint, it would help us to track asteroids better," Gray said. "The care that's given to low Earth orbit satellites has not been applied to those in high Earth orbits because people figured it really doesn't matter. My hope is that, with the U.S. now considering a return to the moon and other countries sending stuff there too, that attitude might change."

Originally published on Live Science.