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Stargazers across the US have been baffled by a mysterious beam of light streaking through the sky.
Around midnight on Saturday, May 17, a glowing streak was visible above the US as far south as New Mexico.
With the aurora active after a surprise geomagnetic storm, many people initially thought the streak was STEVE - a white-mauve light emitted by rivers of charged particles.
However, astronomers have now revealed the true explanation for this bizarre phenomenon.
According to Dr Jonathan McDowell, an astronomer who tracks objects in space, the light was caused by a rocket dumping fuel.
Just an hour or so before the light became visible, Chinese startup LandSpace Technology launched a methane and oxygen-fuelled Zhuque-2E Y2 rocket.
Dr McDowell says the most likely source of the light was this rocket's second stage, releasing its 'Methalox' rocket fuel at about 155 miles (250km) above the ground.
Once released into space, the chemicals in the fuel react with plasma in the Earth's ionosphere to create an eerie whitish glow, just like the one seen above the US.
Stargazers have been baffled after spotting a stunning streak of white light streaming across the sky
People in the US as far south as Mexico spotted a glowing beam of light emerge around midnight on Saturday, May 17
As the glowing streak appeared in the sky, many astronomers' first thought was that they were witnessing a rare space weather phenomenon called STEVE.
Over the night of May 17, the Earth was experiencing a moderate (G2 class) geomagnetic storm after being hit by material from a solar eruption.
The enormous 'bird wing' eruption had originally been predicted to miss Earth, but the wave of material was wider than expected, and the planet was hit with a glancing blow.
Although STEVE is not part of the aurora, it is also caused by space weather and appears like a glowing river of whitish-mauve light in the sky.
In a post on X, photographer Tyler Schlitt captured the event, writing: 'Just saw STEVE with my friends here in Southern Kansas is 45 minutes north of Greensburg!'
However, it soon became apparent that this was no natural phenomenon.
Writing on X, Dr McDowell said: 'TLEs confirm the Zhuque-2 upper stage passed over the US Four Corners area at 0525 UTC May 17 and is the source of the unusual luminous cloud seen by many observers.'
The Zhuque-2 rocket was launched by LandSpace Technology from the Dongfeng Commercial Space Innovation Test Area in northwest China at 04:21 UTC.
While many thought it was a rare space weather phenomenon called STEVE, astronomers have revealed that it was actually caused by a Chinese Zhuque-2 rocket (pictured) dumping methane and oxygen fuel after launching hours earlier
According to Dr McDowell's tracking, the upper stage of the rocket then passed northward over America around 05:24 UTC (11:24 local time).
Unlike most rockets, LandSpace Technology uses a mixture of liquid oxygen and methane called Methalox as fuel.
LandSpace Technology says it was the first company in the world to successfully launch a Methalox rocket in 2023, and this was the fifth flight of its updated Zhuque-2 rocket.
Methalox is increasingly being targeted as a potential spaceflight fuel because it is cheaper, more environmentally friendly, and could potentially be produced on Mars.
That would mean crewed expeditions to the red planet would be able to save weight by not bringing fuel for the return journey.
There are two ways that dumping fuel can cause a glowing streak in the sky.
The first is if the fuel is dumped near dawn or shortly after sunset, allowing frozen crystals of fuel to reflect the light coming over the horizon.
But since this glowing streak appeared around midnight, that isn't a likely option.
Astronomer Dr Jonathan McDowell tracked the path of the rocket (orange) over the US, matching the reports of sightings
This plume was not an aurora, and it was not STEVE. We believe it is related to a rocket launch in China. About an hour before the plume appeared (5:39 UTC), Chinese launch startup Landspace launched the ZhuQue-2E rocket from the Jiuquan Satellite Launch Center (4:12 UTC). It… pic.twitter.com/FEcwhfxbZT
— Oppenheimer Ranch Project (@Diamondthedave) May 17, 2025The second way Methalox can glow is when the fuel itself has a chemical reaction with components of the upper atmosphere.
When carbon, hydrogen, and oxygen - the components of Methalox fuel - enter the charged part of the atmosphere known as the ionosphere, they can react to produce light.
In 2021, a team of physicists led by Paul Bernhardt of the US Naval Research Laboratory found that a plume of fuel entering the ionosphere at night could 'yield a long-lived glow that can be observed from ground or space.'
Since the rocket dumped its fuel at 155 miles (250km) in the middle of the ionosphere, these reactions might explain why the fuel trail glowed so brightly.
This is not the first time that a rocket dumping its fuel has produced a spectacular display over the US.
SpaceX's Falcon 9 rockets routinely create impressive patterns that have left observers on the ground utterly baffled.
The only difference is that SpaceX's fuel dumps typically produce sprawling spiral patterns, rather than the straight, glowing streak spotted on Saturday.
WHAT IS SPACE JUNK? MORE THAN 170 MILLION PIECES OF DEAD SATELLITES, SPENT ROCKETS AND FLAKES OF PAINT POSE 'THREAT' TO SPACE INDUSTRY
There are an estimated 170 million pieces of so-called 'space junk' - left behind after missions that can be as big as spent rocket stages or as small as paint flakes - in orbit alongside some US$700 billion (£555bn) of space infrastructure.
But only 27,000 are tracked, and with the fragments able to travel at speeds above 16,777 mph (27,000kmh), even tiny pieces could seriously damage or destroy satellites.
However, traditional gripping methods don't work in space, as suction cups do not function in a vacuum and temperatures are too cold for substances like tape and glue.
Grippers based around magnets are useless because most of the debris in orbit around Earth is not magnetic.
Around 500,000 pieces of human-made debris (artist's impression) currently orbit our planet, made up of disused satellites, bits of spacecraft and spent rockets
Most proposed solutions, including debris harpoons, either require or cause forceful interaction with the debris, which could push those objects in unintended, unpredictable directions.
Scientists point to two events that have badly worsened the problem of space junk.
The first was in February 2009, when an Iridium telecoms satellite and Kosmos-2251, a Russian military satellite, accidentally collided.
The second was in January 2007, when China tested an anti-satellite weapon on an old Fengyun weather satellite.
Experts also pointed to two sites that have become worryingly cluttered.
One is low Earth orbit which is used by satnav satellites, the ISS, China's manned missions and the Hubble telescope, among others.
The other is in geostationary orbit, and is used by communications, weather and surveillance satellites that must maintain a fixed position relative to Earth.
