Five months ago, a Chinese weather satellite suddenly disintegrated.

It was not clear why, but 21 pieces broke off from the probe on March 18, according to a tweet days later from the US Space Force’s 18th Space Control Squadron, which monitors artificial objects in Earth’s orbit.

Yunhai 1-02 had been sent into orbit from the Gobi Desert in September 2019 – its mission to observe oceans, the atmosphere and space, and to prevent and mitigate disasters.

Chinese media seized on speculation online that its fate was related to US weather satellite NOAA-17, which had broken apart 10 days before and created debris.

The China National Space Administration did not release a statement on the incident at the time.

But on Sunday, astrophysicist Jonathan McDowell found the culprit: Yunhai 1-02 was hit by debris from a Russian rocket that launched a military radio surveillance satellite, Tselina-2, in 1996.

“37 debris objects … have been catalogued so far from the break-up – there are likely to be more. This looks to be the first major confirmed orbital collision in a decade,” McDowell, from the Harvard-Smithsonian Centre for Astrophysics in the US, said in a tweet.

Collisions with space debris in low-Earth orbit – less than 2,000km (1,240 miles) above the Earth’s surface – remain a concern for space agencies worldwide. The increasing density of space junk makes launches more difficult and can render satellites unusable if they smash into something.

Scientists are also concerned about the Kessler syndrome – a chain reaction in which collisions produce more debris, which in turn makes collisions more likely.

“We are faced with a future in which low-Earth orbit will see an increased amount of debris and increased risk of collision and an increased number of serious collisions,” McDowell said.

It could reach a stage where there is so much space junk that it becomes too difficult to operate in low-Earth orbit. But the astrophysicist said this scenario could be avoided if large and abandoned satellites and rocket stages were cleaned up in the next few decades.

When satellites collide with each other in orbit it can produce thousands of pieces of debris. However, that space debris can be removed by putting it on a re-entry trajectory so that it burns up in the atmosphere, though these operations are expensive because the satellites are on different orbital inclinations.

“It’s actually very expensive in fuel to change from one inclination to another. And you probably need a different garbage satellite mission for every inclination range,” McDowell said, adding that countries were still experimenting in isolation on such missions.

“We’ll do a little and we’ll just keep it on the edge of being OK,” he said of how governments were likely to handle the problem of space junk. “I’m basing that on how we’ve dealt with every other environmental problem that humanity’s ever faced.”

McDowell discovered what happened to Yunhai 1-02 after seeing a note on the Space-Track.org website, which publishes orbital data and is run by the US Combined Force Space Component Command.

The note said debris labelled as “object 48078” had “collided with satellite”. The object – a fragment of the Zenit-2 Russian rocket used to launch surveillance satellites – was added to the website’s object catalogue in March, when Yunhai 1-02 broke up.

The Chinese satellite and object 48078 had passed within 1km of each other – within the tracking system’s margin of error – at 7.41am Coordinated Universal Time on March 18, McDowell said on Twitter.

Amateur astronomers say they have detected signals from Yunhai 1-02 since the break-up and orbital corrections have been observed, but the extent to which the satellite remains functional is unknown.

The China National Space Administration and Roscosmos, the Russian space agency, did not respond to requests for comment.

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