Tens of thousands of meteorites have been found on Earth, but the vast majority remain shrouded in mystery. These rocks come from space, of course, but determining their exact origin, in the solar system or beyond, is difficult without knowing their flight paths.
But now, researchers believe they have linked a meteorite discovered in the Austrian Alps decades ago with bright flashes of light from a space rock hurtling through our planet’s atmosphere. It’s rare to link a meteorite to its parent “fireball,” and these results show the utility of combing through old data sets, the research team suggests. Their findings were published in the journal Meteoritics & Planetary Science in May.
In 1976, Josef Pfefferle, a forest ranger, was clearing debris from an avalanche near the Austrian village of Ischgl when he noticed a strange-looking rock. He brought the fist-sized black stone back to his house and placed it in a box.
Thirty-two years later, Mr. Pfefferle heard news of a meteorite discovered in Austria and wondered if his strange rock might also be from space. He decided to bring his rock to a university to be analyzed.
Mr. Pfefferle’s find turned out to be a meteorite and, at over two kilograms, a relatively large one. Moreover, its unchanged appearance suggested that it had fallen to Earth only shortly before Mr. Pfefferle retrieved it.
“It was such a fresh meteorite,” said Maria Gritsevich, a planetary scientist at the University of Helsinki in Finland, who led the latest study. “It was so well preserved.”
Dr. Gritsevich and her colleagues hypothesized that if the Ischgl meteorite had fallen to Earth relatively recently, perhaps its arrival had been captured on film. A network of 25 sky-watching cameras spread across southern Germany had been collecting long-exposure images of the night sky since 1966. By the time the network shut down in 2022, it had recorded over 2,000 fireballs .
“It made more sense to trace it back to the most recent fireball seen in the area,” said Dr. Gritsevich.
She and her team scanned negatives of fireball images stored at the German Aerospace Center in Augsburg. After digitizing the images, the researchers assessed various parameters about the incoming meteors, such as their masses, shapes, velocities and entry angles. Using these data, the researchers tracked down a dozen events that most likely produced sizable meteorites. Only three had occurred before 1976.
The team reconstructed the trajectory of each of those three fireballs and calculated where the meteorites would be found. There was only one match where the Ischgl meteorite was found. This led researchers to conclude that the fireball that shot down the horizon in the early morning hours of November 24, 1970, gave birth to the Ischgl meteorite.
“It was an exact match,” said Dr. Gritsevich.
She and her colleagues calculated that the incoming meteor fell to Earth at a speed of about 45,000 miles per hour. That’s fast, but within the range of meteoroids born in the solar system, said Dr. Gritsevich. Something that came from beyond the solar system, on the other hand, would have traveled much faster, she added.
The meteor that produced 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, said Dr. Gritsevich.
Linking a meteor to where it was born is important, said Marc Fries, a planetary scientist at NASA’s Johnson Space Center in Houston, who was not involved in the research. “It goes from just being a rock you find on Earth to a rock that comes from a certain place in the solar system,” he said. To date, about 50 meteorites have had their orbits determined; Ischgl is the third oldest of them.
The case of the Ischgl meteorite is not yet closed, however, said Peter Brown, a planetary scientist at Western University in Ontario, who was also not involved in the research. After all, he said, there’s always the possibility that this meteorite has been sitting on Earth’s surface for much longer than six years. The alpine environment in which it fell could have preserved the rock quite well.
“It really could have been there for decades and potentially centuries,” said Dr. Brown.
Still, he said, there’s a neat story here: “It’s great to show there’s value to this old data.”