A 3- ton (2.7 metric tons) discarded rocket stage will smash into the moon Friday (March 4), but its origins are still disputed. Several astronomers who have been tracking the piece of space junk say it is from China, although Chinese officials disagree.
The discarded rocket stage will be traveling at a blistering 5,771 mph (9,288 km/h) when it hits the Hertzsprung crater on the moon's far side at 7:25 a.m. EST (1225 GMT) Friday. The energy from the collision is expected to punch out a shallow crater and send a plume of moon dust hundreds of miles high.
The event will mark the first time that any space junk has accidentally collided with the lunar surface. Many experts now 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 claim that their upper stage burned up in Earth's atmosphere years ago. Because the impact will occur on the moon's far side, it could take scientists weeks, or even months, to find the crater and any lingering evidence which could settle the case of the rocket's controversial origins.
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 was the first astronomer to predict that the debris would collide with the moon after it was first 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, a project that uses telescopes in Arizona to scan 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.
Gray initially identified the errant space junk as the upper stage of a SpaceX Falcon 9 rocket, sent to space in February 2015 to deliver the Deep Space Climate Observatory (DSCOVR), a satellite designed to monitor both solar storms and Earth's climate, to a gravitationally stable Lagrange point between the sun and Earth. Gray thinks that, after completing its task, the rocket's second stage ran out of fuel and began tumbling around Earth and the moon in an unpredictable orbit.
But after being contacted by Jon Giorgini, an engineer at NASA's Jet Propulsion Laboratory who tracks active spacecraft, Gray realized he was wrong. The DSCOVR spacecraft's trajectory didn't take that object very close to the moon and, therefore, made it unlikely that a piece of the craft would end up hurtling into Earth's lunar neighbor. Going back to his records, Gray discovered another spacecraft which fitted much more 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 will be the object that hits 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 had never deorbited.
"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, the Jet Propulsion Laboratory's Center for Near Earth Object Studies reran Gray's orbital analysis, confirming its accuracy, and a University of Arizona team even looked at the spectrum of the sunlight being reflected by the distant, moon-bound object's paint, confirming that it matched the paint of the Chang'e 5-T1.
The space junk is projected to hit the moon's equator on its far side, meaning that the impact will go unobserved from Earth. Satellites orbiting the moon, such as NASA's Lunar Reconnaissance Orbiter and India's Chandrayaan-2 spacecraft, will not be in the right spot to capture the collision but will most likely be used to identify the resulting impact crater. It could take many months for scientists to spot the new lunar hole, but many are hoping the images could help them better understand the moon's subsurface contents.
Although this will be 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 key signatures of water ice. The Saturn V rockets of NASA's Apollo missions were also deliberately disposed of by being fired 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.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.
Ben Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.