The remaining rocket will smash into the far side of the moon at 5,800 mph (9,300 kph) on Friday, out of the prying eyes of telescopes. It can take weeks, even months, to confirm the effect with satellite images.
Experts believe it’s been rolling randomly through space, ever since China launched it nearly a decade ago. But Chinese officials doubt it’s theirs.
Regardless of who it is, scientists predict that the object will dig a hole 33 feet to 66 feet (10 to 20 meters) wide and send moon dust flying hundreds of miles (kilometres) across the barren, blistered surface.
It’s relatively easy to keep track of low-orbit space junk. Objects blasting deep into space are unlikely to collide with anything, and these distant pieces are usually forgotten, except for a few observers who enjoy playing the celestial detective on the side.
SpaceX originally took a rap for the upcoming lunar litter after asteroid tracker Bill Gray set its collision course in January. He corrected himself a month later, saying the “mysterious” object was not a SpaceX Falcon rocket in the upper stage of NASA’s 2015 Deep Space Climate Observatory launch.
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 reentered Earth’s atmosphere and burned up.
But there have been two Chinese missions with similar names – the test flight and the mission to return to the moon in 2020 – and US observers believe the two are getting mixed up.
The US Space Command, which tracks low-lying space junk, confirmed Tuesday that China’s upper stage of the 2014 lunar mission was never de-orbited, as previously described in its database. But she couldn’t confirm the country of origin of the thing about to hit the moon.
“We are focused on things closest to Earth,” a company spokesperson said in a statement.
Gray, the mathematician and physicist, said he was now confident it was China’s missile.
“I’ve become a little more cautious in such matters,” he said. “But I really don’t see any way anything else could be.”
Jonathan McDowell of the Harvard and Smithsonian Center for Astrophysics supports Gray’s revised assessment, but notes: “The effect will be the same. It will leave another small crater on the Moon.”
The moon already holds countless craters, reaching 1,600 miles (2,500 km). With little or no real atmosphere, the Moon is defenseless against a constant barrage of meteors and asteroids, and the occasional incoming spacecraft, including a few deliberately crashed for the sake of science. With no weather, there is no wear and so impact pits last forever.
China has a lunar lander on the far side of the moon, but it will be too far from detecting Friday’s impact north of the equator. NASA’s Lunar Reconnaissance Orbiter will also be out of range. India orbiting the moon Chandrayaan-2 is unlikely to pass at that time either.
“I was hoping something (significant) would hit the moon for a long time,” Gray said. “Ideally, it would have hit the near side of the moon at some point where we can actually see it.”
Pinning the next hit on Elon Musk’s SpaceX, Gray took another look after an engineer at NASA’s Jet Propulsion Laboratory questioned his claim. Now, it is “fully convinced” that it is a Chinese rocket part, based not only on orbital tracking for its 2014 launch, but also data received from the short-lived Ham Radio experiment.
The JPL Center for Near-Earth Object Studies supports Gray’s re-evaluation. A team from the University of Arizona recently identified a segment of a Chinese Long March rocket from light reflected off its coating, during telescope observations of the deflecting cylinder.
They are about 40 feet (12 m) long and 10 feet (3 m) in diameter, and they do somersaults every two to three minutes.
Gray said SpaceX never contacted him to challenge his original claim. Nor are the Chinese.
“It’s not a SpaceX problem, nor is it a China problem,” Gray said. “Nobody is particularly keen about what they do with junk in this kind of orbit.”
According to McDowell, tracking the remnants of a deep space mission like this is tricky. The moon’s gravity can change the trajectory of an object during flight, creating uncertainty. McDowell noted that there is no readily available database, except for those “bundled together” by himself, Gray and a couple others.
“We are now in an era where many states and private companies are putting things into deep space, so it is time to start tracking them,” McDowell said. “At the moment there is no one, only a few fans in their spare time.”
Associated Press video producer Olivia Zhang and Beijing-based video journalist Sam McNeill contributed to this report.
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