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For some citizens it was certainly a disturbing phenomenon what they saw over the weekend: a bright beam moved through the sky on Saturday night, a round ball of fire was formed, which glowed for seconds. An observer reported a greenish color. Then the object disintegrated into various parts high in the sky and was finally no longer visible.
The object was discovered in the sky, especially in southwestern Germany, between Cologne, Frankfurt and Stuttgart. “We have a good hundred sightings in this area,” says Dieter Heinlein of the German Aerospace Center (DLR). But DLR also received eyewitness reports on the phenomenon from the north. And you could even hear the event acoustically.
In Freyung, in Lower Bavaria, on the border between Germany, the Czech Republic and Austria, the infrasound station »I26DE« constantly listens to pressure waves below the frequency range that can be heard by humans. It is part of a global monitoring network of the Comprehensive Nuclear-Test-Ban Treaty Organization, which aims to track banned nuclear tests.
Some of the systems analyze seismic waves, others listen in the oceans, and still others look for radioactive particles in the atmosphere. And 60 stations like Freyung’s listen to what’s known as infrasound. Barometers still perceive pressure differences of only one billionth of normal atmospheric pressure. Explosions, jet jets or fragments of space can be responsible for vibrations in the air.
The Federal Institute of Geosciences and Natural Resources (BGR) in Hannover is responsible for the station. At the request of SPIEGEL, they leaned on the “I26DE” data on Saturday. And BGR expert Christoph Pilger confirms: “At 7:01 pm local time, our station recorded a clear infrasonic peak from the northwest.”
The fireball was observed by observers in the sky around 6:40 p.m. The fact that the station only registered it about 20 minutes later is due to the speed of sound, Pilger said. In any case, it was “a larger sign” that was “clearly legible”.
What kind of celestial phenomenon was it that you could not only see, but even hear?
DLR’s Dieter Heinlein is currently assuming an asteroid fragment that has entered the atmosphere. He is the technical director of the DLR fireball network, a network of 25 camera stations in Germany, the Czech Republic, Belgium, Luxembourg and Austria that document and research such phenomena.
Presumably sky watchers witnessed a rather rare event. While most people have seen a meteor, popularly known as a shooting star, lighter fireballs are not that common. On an annual average, the DLR fireball network only recorded around 30 such events.
Unlike a normal shooting star, which generally shines for less than a second, a fireball can burn for up to five seconds, and in rare cases even longer. Sometimes the ball changes color or appears to explode at the end of its trajectory. In the case of shooting stars, it is usually just material the size of a grain of dust that is heated by air resistance; In the case of fireballs, also known as bolides, they are massive bodies that impact the atmosphere at speeds of several kilometers per second. They are made of stone or metal and are at least one centimeter high (read more about the differences between the terms here).
Space stones the size of a table tennis ball
When the meteors in the sky turn into a ball of fire, this event excites the experts. Because while shooting stars are completely burned up in the atmosphere, the remnants of the cosmic bulge can reach the surface of the earth. “This is cosmic material that is given to us for free,” says Heinlein. Sometimes there is a possibility that all the material has not been used. That only happened in November when a racing car was sighted over Austria. But no fragments of this event have yet been found.
Perhaps now there are some black stones somewhere in Germany that have had a long journey through space. To find them, DLR researchers are now evaluating all the information they can get. First of all, the camera recordings of his own network, but also the images and descriptions of the laity. This can result in data on the trajectory of the fireball, which can be used to delineate possible sites.
The remnants of such fireballs are unique testimony to the early phase of our solar system more than four billion years ago, when planets formed around our central star. But not all the matter in the disk of gas and dust around the young star made it to beautiful round planets. The gravitational pull of the giant planet Jupiter prevented them from clumping together, causing them to become misshapen lumps no more than a few hundred kilometers in size. Hundreds of thousands of them are buzzing between Mars and Jupiter in the asteroid belt. Sometimes they collide with each other and splinter. And sometimes the force of the impact knocks stone and metal structures into the ground.
Support from “unpaid astronomers”
It is precisely the fresh remains of this trip that interest researchers like Heinlein. Unlike meteorites that were found on Earth at some point, scientists can reconstruct the path of travel back to its starting point in the asteroid belt for current events.
But it is very rare for researchers in Germany to find the remains of the extraterrestrial fragments. This was achieved in April 2002 when a chunk at a height of 22 kilometers near Neuschwanstein broke into several fragments, of which around six kilograms of material could be collected on the ground. And in Renchen in Baden-Württemberg, astronomy fans also found some snippets of a 2018 event, a stroke of luck for science.
In this context, Heinlein expressly values the work of the laity on whom science depends. Not all entries into the atmosphere are documented by a camera. That is why it is important that amateur researchers make their data available. However, he doesn’t like the term because space enthusiasts often work very professionally. “They are actually unpaid astronomers,” he says.
