Astronomers Reveal the Cosmic History of the Ischgl Meteorite

16:22, May 29, 2024

They were able to establish the weight, age, and time of its fall to Earth

An international team of scientists conducted a study to discover the fascinating cosmic history of the Ischgl meteorite. Astronomers analyzed observations of the German part of the European bolide network for the entire period of its existence (57 years). As a result of the analysis of records of bolides and data on weather conditions, scientists have determined the exact time of the meteorite fall, calculated the trajectory of the bolide, the weight of the meteoric body at the entrance to the atmosphere, the degree of dispersion and weight of fragments after the fall, the orbit of the space body before the collision with the Earth. The work of the team was led by Maria Gritsevich, Adjunct Professor at the University of Helsinki and Senior Researcher at the Ural Federal University. The authors published a description of the meteorite, its data and research methods in the journal Meteoritics & Planetary Science.

“The discovery of the Ischgl meteorite is extremely interesting. In June 1976, on a mountain road at an altitude of 2,000 meters above sea level, about two kilometers northwest of the Tyrolean town of Ischgl in Austria, forest ranger Josef Pfefferle, while clearing the remains of an avalanche, found a stone weighing about 1 kg, completely covered with fresh fusion crust. The rock had probably been carried with the avalanche from a higher area of the mountain. However, Mr. Pfefferle did not attach any special significance to it and put it in a box at home, where he kept it for more than 30 years. In 2007, Austrian media reported a high-profile case involving a meteorite, the third Neuschwanstein fragment discovered near Reutte in Tyrol, Austria. The reports reminded Mr. Pfefferle of his 1976 discovery. In 2008, he took the sample to the University of Innsbruck, where it was determined that the find was a meteorite”, Maria Gritsevich explains the story.

The sample was classified as a chondrite of excellent preservation LL6 with weathering grade W0. This means that relatively little time elapsed between the meteorite's fall and its discovery and that the conditions in which the meteorite was located before its discovery were relatively good (no sudden temperature changes, strong winds, etc.).

“Our work aimed to establish a possible connection between a meteorite find and a recorded meteorite event. To date, science knows of only about 50 cases where it was possible to find a meteorite with an associated atmospheric trajectory and orbit. The possibility of associating a meteorite with a W0 degree of weathering - with minimal signs of exposure to terrestrial conditions - with such information (trajectory and orbit) is key to understanding the processes that determined the history of the formation and evolution of the Solar System", explains Maria Gritsevich.

Scientists studied images of the European network from cameras installed in Germany, which covered an area of 400 thousand square kilometers. The data were analyzed from 1966 to 2022 (when the network completed its work). Images dated after the discovery of a meteorite in the mountains were needed to assess the statistics of meteorite falls. As the scientists explain, more than 2000 bolides were recorded during the operation of the bolide network. However, the vast majority of them disintegrated completely in the atmosphere. Only 12 cases could be classified as meteorite impact events with a mass of more than 0.5 kg.

“In the night of November 23-24, 1970, the bright bolide EN241170 was photographed simultaneously by 10 stations of the European network. The time of the meteorite's impact - 01:47 UTC - was also reported by eyewitnesses one minute apart. The DLR archive in Augsburg still has 10 original negatives of the phenomenon. This number of records is a rare fortune, especially considering the year of the meteorite's fall - 1970. Thus, the trajectory of the bolide was visible for the entire duration of 7.4 seconds”, says Jaakko Visuri, an astronomer with the Finnish Bolide Network.

In addition, the researchers analyzed archival data from the German Meteorological Service. The weather conditions helped to calculate the dark phase of the meteorite's flight and the area to which the fragments flew, the number of which could reach several dozen. Also, according to scientists' calculations, the body's initial mass at the entry into the atmosphere was 95-165 kg. It is estimated that 24 to 37 kg (the mass of all fragments) fell to the ground. The analysis of cosmogenic radionuclides allowed to determine the age of the meteorite - about 7-9 million years.

“The Ischgl meteorite can now be listed in the Meteorite Bulletin database as a 'confirmed fall' and no longer in the 'find' category. As of 2024, Ischgl is one of nine confirmed meteorite falls in present-day Austria, together with Mauerkirchen, Mühlau, Minnichhof, Lanzenkirchen, Prambachkirchen, Ybbsitz, Neuschwanstein and Kindberg. After the Příbram and Lost City cases, Ischgl is the third oldest fall where a meteorite was found and a heliocentric pre-collision orbit was determined. I believe other notable bolide events should be studied with the current methods and knowledge. By combining historical records and modern approaches, we will gain more information and better understand the origin and characteristics of meteorite impacts”, concludes Jarmo Moilanen, a PhD student at the University of Helsinki.

The study involved astrophysicists from Finland, Russia, Sweden, Switzerland, Germany, Spain, Austria, the United Arab Emirates, and Slovakia.

Anna Marinovich

The news article was translated by UrFU International Marketing Office.
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