Tens of thousands of meteorites have been found on Earth, but the vast majority of them remain shrouded in mystery. These rocks obviously come from space, but determining their exact origin – in the solar system or even beyond – is difficult without knowing their trajectories.
But now researchers believe they have linked a meteorite discovered decades ago in the Austrian Alps to bright flashes of light from a space rock hurtling through our planet’s atmosphere. It’s rare for a meteorite to be linked to its “fireball,” and these results show the usefulness of combing through old data sets, the research team said. Their findings were published in May in the journal Meteoritics & Planetary Science.
In 1976, forester Josef Pfefferle was clearing the remains of an avalanche near the Austrian village of Ischgl when he noticed a strange-looking stone. He brought the fist-sized black stone home and stored it in a box.
32 years later, Mr. Pfefferle heard on the news about a meteorite discovered in Austria and wondered if his strange stone could also have come from space. He decided to take the stone to a university for analysis.
Mr. Pfefferle’s find turned out to be a meteorite, and a relatively large one at that, weighing over two pounds. In addition, its unweathered appearance suggested that it had fallen to earth shortly before Mr. Pfefferle discovered it.
“It was such a young meteorite,” said Maria Gritsevich, a planetary scientist at the University of Helsinki in Finland who led the current study. “It was so well preserved.”
Dr. Gritsevich and her colleagues suspected that if the Ischgl meteorite had fallen to Earth relatively recently, its arrival might have been captured on film. A network of 25 sky cameras spread across southern Germany had been collecting long-exposure images of the night sky since 1966. By the time the network ceased operations in 2022, it had recorded over 2,000 fireballs.
“The most logical thing was to attribute it to the last fireball seen in the area,” said Dr. Gritsevich.
She and her team searched for negatives of images showing fireballs stored at the German Aerospace Center in Augsburg. After digitizing the images, the researchers estimated various parameters of the approaching meteors, such as their mass, shape, speed and angle of entry. Using this data, the researchers were able to identify a dozen events in which large meteorites most likely struck. Only three of these events had occurred before 1976.
The team reconstructed the trajectory of each of these three fireballs and calculated where meteorites would most likely be found. There was only one match, with the location of the Ischgl meteorite. From this, the researchers concluded that the fireball that raced low over the horizon in the early hours of November 24, 1970, had produced the Ischgl meteorite.
“This one was a perfect fit,” said Dr. Gritsevich.
She and her colleagues calculated that the meteorite fell to Earth at a speed of about 72,000 kilometers per hour. While that is fast, it is still within the range of meteoroids born in the solar system, Dr. Gritsevich said. Something coming from outside the solar system would have been much faster, she added.
The meteoroid that created the 1970 fireball once orbited the sun relatively close to Earth, the team estimated. It probably did not come from the main asteroid belt between Mars and Jupiter, which is the source of many meteoroids, Dr. Gritsevich said.
Assigning a meteorite to its birthplace is important, said Marc Fries, a planetary scientist at NASA Johnson Space Center in Houston who was not involved in the research. “It’s no longer just a rock you find on the ground, but a rock that comes from a specific place in the solar system,” he said. To date, the orbits of about 50 meteorites have been determined; Ischgl is the third oldest of these.
The fall of the Ischgl meteorite is not yet over, says Peter Brown, a planetary scientist at Western University in Ontario, who was also not involved in the research. After all, there is still the possibility that this meteorite could have been on the surface of the Earth for much longer than six years. The alpine environment in which it fell could have preserved the stone quite well.
“It may actually have been there for decades and possibly centuries,” Dr. Brown said.
Still, he said, there’s a nice story here: “It’s great to show that this older data is valuable.”