Celestial Spirals: The Atmospheric Physics of Rocket Fuel Dumps

A Breathtaking Dance in the Night Sky

Imagine gazing up at the tranquil, star-dusted canvas of the night sky, only to be met by a silent, luminous whirlpool of light. A ghostly, glowing spiral, sometimes tinged with a delicate blue, grows and unfurls like a celestial phantom. For a few mesmerizing minutes, it dominates the heavens before slowly fading into the darkness. This is not the stuff of science fiction, nor is it a portent of an alien invasion, though many initial eyewitnesses might be forgiven for thinking so. Across the globe, from the aurora-lit skies of Alaska and Norway to the UK and the islands of the Pacific, these "celestial spirals" have left onlookers in a state of awe and confusion.

"Anyone else just see this in the sky? It just kept spinning," one resident of Ashton-under-Lyne in the UK posted on social media after a prominent sighting. Another from Horwich, Bolton, described it as "absolutely beautiful flying over Horwich." In Bristol, an observer initially mistook it for an airplane before the spectacle began. “It suddenly went blurry… then all of a sudden it started shooting out these spiral arms and spinning," he recounted. "I realised straight away it was SpaceX because I've seen it so much on YouTube, but I can totally see how others would have been weirded out by it – it really did look alien.”

These breathtaking displays, often dubbed "SpaceX spirals" due to their frequent association with the company's launches, are a beautiful and increasingly common byproduct of our modern space age. They are, in essence, the atmospheric footprint of rocket fuel dumps, a stunning intersection of human technology and the physics of the upper atmosphere.

The Science Behind the Spectacle: Unveiling the Mystery

The explanation for these celestial spirals is as fascinating as the sight itself. They are typically created during the final phases of a rocket's mission, specifically by the rocket's second stage after it has deployed its payload, such as a satellite. To ensure a safe and controlled de-orbit and prevent the risk of explosion upon reentry, any leftover propellant is vented into space.

This is where the magic begins. This venting often occurs at altitudes ranging from 100 kilometers to over 300 kilometers, placing it in the mesosphere and thermosphere. At these heights, the atmosphere is a near-vacuum. When the liquid propellant is released into this environment, it undergoes a process of rapid, almost instantaneous, boiling and freezing. The extreme low pressure causes the liquid to boil, and the energy required for this phase change is drawn from the liquid itself, causing it to cool and freeze into a cloud of tiny ice crystals. This is a much faster way to freeze a liquid than simply exposing it to a cold environment.

The crucial element that transforms this cloud of frozen fuel into a spiral is the rotation of the rocket's upper stage. To maintain stability or to deploy multiple satellites into different positions, the rocket stage is often set into a slow spin. As it spins, it releases the propellant like a celestial garden sprinkler, creating a perfect, expanding spiral of ice crystals.

For this ethereal spiral to become visible to us on the ground, one final ingredient is needed: sunlight. These events are most often witnessed shortly after dusk or before dawn. From our perspective on the darkened surface of the Earth, the sun has already set or has yet to rise. However, at the extreme altitudes of the fuel dump, the cloud of ice crystals is still bathed in sunlight. These countless tiny crystals act like a vast, diffuse mirror, reflecting the sunlight back down to Earth and creating the luminous, otherworldly spiral we see against the twilight sky. The spectacle typically lasts for several minutes before the crystals disperse and the spiral fades from view.

A Tale of Two Spirals: Comparing the Celestial Dancers

While SpaceX's Falcon 9 rockets are most frequently associated with these phenomena, they are by no means the only celestial artists. Similar events have been attributed to Russian and Chinese rocket launches, each with their own subtle characteristics.

The Famous Norwegian Spiral of 2009:

Perhaps the most dramatic and widely publicized of these events was the "Norway spiral" of December 9, 2009. Before dawn, Norwegians were stunned by a massive, complex spiral of light, consisting of a blue beam at its center with a grayish-white spiral emanating from it. The sheer scale and unusual appearance sparked a frenzy of speculation, from UFOs and wormholes to secret military experiments. The truth, as it later emerged, was a failed test of a Russian Bulava submarine-launched ballistic missile. The missile's third stage malfunctioned, causing it to spin out of control while still under thrust, venting its propellant in a spectacular, albeit unintentional, display. The two distinct colors of this spiral were likely due to different components of the propellant and their interaction with sunlight at high altitude; the white spiral from neutral gases and condensed particles, and the blue "trail" from ionized gases.

SpaceX and the Proliferation of Spirals:

With the increasing launch cadence of SpaceX's Falcon 9 rockets, sightings of these spirals have become more common in recent years. The Falcon 9's upper stage typically uses a highly refined kerosene known as RP-1 and liquid oxygen (LOX) as its propellant. The spirals they create are often described as a swirling blue-white glow. The procedure of venting fuel from a spinning second stage is a deliberate part of SpaceX's de-orbit procedure for its reusable rockets. In fact, for missions with multiple satellites heading to different orbits, the upper stage may need to spin more during deployment, increasing the likelihood of a visible spiral during the subsequent fuel dump.

Chinese Rocket Spirals:

China has also contributed to this celestial light show. In June 2021, a spiral was witnessed over the Pacific, which was later confirmed to be from the second stage of a Chinese Long March 2C rocket. These events demonstrate that the physics behind the phenomenon is universal, regardless of the rocket's origin. The key ingredients remain the same: a spinning upper stage, a fuel dump at high altitude, and the right lighting conditions.

The Unseen Aftermath: Environmental Considerations

While these celestial spirals are undeniably beautiful, they are a visible reminder of the direct injection of pollutants into the upper layers of our atmosphere. The environmental impact of these fuel dumps is a growing area of concern for scientists.

The effects vary depending on the type of fuel used and the atmospheric layer in which it is released:

Kerosene-based fuels (like SpaceX's RP-1): The combustion of kerosene produces black carbon, or soot. When released into the stratosphere, these particles are highly efficient at absorbing solar radiation and warming this layer of the atmosphere. This warming can, in turn, accelerate chemical reactions that deplete the ozone layer. The radiative forcing of black carbon emitted by rockets is estimated to be almost 500 times greater than that of soot from surface sources.
Solid Rocket Motors (like those used in the Space Shuttle and some other launch systems): These motors release chlorine and aluminum oxide particles directly into the stratosphere. Chlorine is a potent ozone-depleting substance, and the surface of the alumina particles can also facilitate ozone-destroying chemical reactions. These particles can persist in the stratosphere for up to four years, accumulating with each launch.
Methane-based fuels (Methalox): Considered a "cleaner" option, methane burns more efficiently than kerosene, producing less soot. While still a greenhouse gas, the overall environmental impact in the upper atmosphere is thought to be less severe than that of kerosene or solid fuels.

These emissions are deposited in the stratosphere and mesosphere, layers of the atmosphere that do not have the rapid weather cycles of the lower troposphere to wash away pollutants. As the frequency of rocket launches by both national space agencies and private companies continues to climb, the cumulative impact of these fuel dumps on the delicate chemistry and temperature balance of the upper atmosphere is a subject of ongoing and increasingly urgent research.

So, the next time you are fortunate enough to witness one of these ethereal spirals gracing the night sky, take a moment to appreciate the stunning display of physics and human ingenuity. But also, consider the unseen environmental footprint left behind in the highest reaches of our atmosphere, a silent testament to our expanding presence beyond the confines of our planet.

A Breathtaking Dance in the Night Sky

The Science Behind the Spectacle: Unveiling the Mystery

A Tale of Two Spirals: Comparing the Celestial Dancers

The Unseen Aftermath: Environmental Considerations

Reference: