A mysterious beam of light streaking through the sky has perplexed astronomers across the United States.
Around midnight on Saturday, May 17, a glowing streak was visible over the United States as far south as New Mexico.
With the aurora active following a surprise geomagnetic storm, many people initially mistook the streak for STEVE, a white-mauve light emitted by rivers of charged particles.
Astronomers have now discovered the true explanation for this bizarre phenomenon.
According to Dr. Jonathan McDowell, an astronomer who tracks spacecraft, the light was caused by a rocket dumping fuel.
LandSpace Technology, a Chinese startup, launched a Zhuque-2E Y2 rocket powered by methane and oxygen about an hour before the light became visible.
According to Dr. McDowell, the most likely source of the light was the rocket’s second stage, which released its ‘Methalox’ rocket fuel approximately 155 miles (250 kilometers) above ground.
Once released into space, the chemicals in the fuel react with plasma in the Earth’s ionosphere, producing an eerie whitish glow similar to the one seen above the United States.
As the glowing streak appeared in the sky, many astronomers assumed they were witnessing a rare space weather phenomenon known as STEVE.
The Earth experienced a moderate (G2 class) geomagnetic storm overnight on May 17 after being hit by material from a solar eruption.
The massive ‘bird wing’ eruption was expected to miss Earth, but the wave of material was larger than expected, and the planet received a glancing blow.
Although STEVE is not a type of aurora, it is caused by space weather and appears as 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 clear that this was not a natural phenomenon.
Dr McDowell wrote on X: ‘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.’
LandSpace Technology launched the Zhuque-2 rocket from the Dongfeng Commercial Space Innovation Test Area in northwest China at 04:21 UTC.
According to Dr. McDowell’s tracking, the upper stage of the rocket passed northward over America around 05:24 UTC (11:24 local time).
LandSpace Technology, unlike most rockets, uses Methalox, a mixture of liquid oxygen and methane, as fuel.
LandSpace Technology claims it was the first company in the world to successfully launch a Methalox rocket in 2023, and this was the fifth flight of its upgraded Zhuque-2 rocket.
Methalox is increasingly being considered as a potential spaceflight fuel due to its lower cost, greater environmental friendliness, and potential for production on Mars.
That means crewed missions to the red planet could save weight by not bringing fuel for the return trip.
There are two ways that dumping fuel can result in a glowing streak in the sky.
The first occurs when fuel is dumped near dawn or shortly after sunset, allowing frozen crystals of fuel to reflect light coming over the horizon.
But since this glowing streak appeared around midnight, that is not a likely explanation.
The second way Methalox can glow is when the fuel reacts with upper-atmosphere components.
When carbon, hydrogen, and oxygen, the constituents of Methalox fuel, enter the charged region of the atmosphere known as the ionosphere, they can react to produce light.
In 2021, physicists led by Paul Bernhardt of the US Naval Research Laboratory discovered 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 (250 kilometers) in the middle of the ionosphere, these reactions could explain why the fuel trail was so bright.
This is not the first time a rocket dumping fuel has caused a spectacular display over the United States.
SpaceX’s Falcon 9 rockets routinely produce stunning patterns that baffle observers on the ground.
The only difference is that SpaceX’s fuel dumps typically produce sprawling spiral patterns, not the straight, glowing streak seen on Saturday.