On the night of March 24, a strange blue spiral appeared in the European sky, prompting a mountain of astonished reactions from observers. But what was it, exactly? A consensus now seems to have emerged among experts—and at the risk of disappointing some, it is probably not an interdimensional portal opened by extraterrestrials.
Shortly after the object's appearance on the evening of March 24, social media was taken over by witnesses, each offering their own little speculation. Some immediately claimed, often with humor, that it was a "portal to another world," potentially opened by intergalactic visitors wandering through our corner of the cosmos.
Definitely not a galaxy
Other, more down-to-earth Internet users also suggested that it could be a galaxy. An understandable reaction, given that the appearance of this object is reminiscent of spiral galaxies like our own Milky Way. A hypothesis quickly dismissed by other, more experienced astronomy observers because of the object's movement, which is completely incompatible with the galaxy track.
And even if the phenomenon had remained perfectly still, the interpretation would be the same. Based on the object's size, it can be calculated that to be visible in the sky, such a galaxy would have to be located a handful of light-years from Earth.
Even if this is a significant distance in absolute terms, it remains close in the context of astronomy; we remain in what is called the Local Group, the cluster of galaxies to which the Milky Way and Andromeda belong. However, this Local Group is now very well documented. The chances of a brand new galaxy, never observed before, appearing in such a spectacular way without warning are therefore completely zero.
A spectacular "SpaceX spiral"
Other observers have therefore argued that the phenomenon was probably linked in some way to an artificial object built by humanity, such as a satellite. And they were probably not so far from the truth. The most likely explanation is that it is what is now called a "SpaceX spiral," in reference to Elon Musk's company.
The Falcon 9 family of rockets consists of two stages: the reusable booster, designed to return to Earth, and the second stage, which carries the payload. The two parts separate shortly after takeoff, at the end of the first phase of the ascent. At this point, the booster begins to rotate and gets rid of some of the remaining fuel before beginning its return to the surface. This helps balance the pressure in the propulsion system and optimize mass distribution within the vehicle, ensuring the descent takes place in the best possible conditions.
Because of the booster's rotation, this jettison creates a spiral-shaped pattern, much like water from a sprinkler. However, the separation typically takes place at an altitude of around 90 kilometers, near the edge of the atmosphere. These liquid propellants, already stored at a very low temperature in the tanks, freeze instantly. They then transform into crystals that strongly reflect light, hence the fact that the structure appears to shine brightly. And since the atmosphere is extremely thin at this altitude, the spiral thus generated can maintain its shape for a long time and continue to follow the trajectory initially described by the vehicle.
At present, these spirals remain relatively rare, especially above European soil. But since SpaceX continues to increase the rate of its launches, it's a safe bet that they will become more and more frequent in the coming years. Good news for photographers... but not necessarily for astronomers, who are increasingly concerned about the impact of visual pollution on the operations of their telescopes.
0 Comments