Tens of thousands of meteorites have been found on Earth, but a vast majority remain shrouded in mystery. These rocks come from space, of course, but pinning down their exact origins, in the solar system or even beyond, is difficult without knowing their flight paths.
But now, researchers believe they have connected 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 with its parent “fireball,” and these results demonstrate the usefulness of combing 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 the remnants of an avalanche near the Austrian village of Ischgl when he noticed an odd-looking rock. He brought the fist-size black stone back to his house and put it in a box.
Thirty-two years later, Mr. Pfefferle heard a news story about a meteorite discovered in Austria and wondered if his weird rock might also be from space. He decided to bring his rock to a university to be analyzed.
Mr. Pfefferle’s find did turn out to be a meteorite, and, at over two pounds, a relatively large one. Furthermore, its unweathered exterior suggested that it had fallen to Earth only shortly before Mr. Pfefferle picked it up.
“It was such a fresh meteorite,” said Maria Gritsevich, a planetary scientist at the University of Helsinki in Finland who led the recent study. “It was so well preserved.”
Dr. Gritsevich and her colleagues surmised that if the Ischgl meteorite had fallen to Earth relatively recently, perhaps its arrival had been captured on film. A network of 25 sky-viewing 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.
“It was most logical to track it back to the most recent fireball seen in the area,” Dr. Gritsevich said.
She and her team hunted down negatives of fireball-containing images stored at the German Aerospace Center in Augsburg. After digitizing the images, the researchers estimated various parameters about the incoming meteors, such as their masses, shapes, velocities and angles of entry. Using that data, the researchers homed in on a dozen events that had 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 meteorites would most likely be found. There was just one match with where the Ischgl meteorite was recovered. This led the researchers to conclude that the fireball that arced low across the horizon in the early morning hours of Nov. 24, 1970 birthed the Ischgl meteorite.
“This one matched exactly,” Dr. Gritsevich said.
She and her colleagues calculated that the incoming meteor fell to Earth at a speed of roughly 45,000 miles per hour. That’s fast but well within the range of meteoroids born in the solar system, Dr. Gritsevich said. Something that came from beyond the solar system, on the other hand, would have been traveling much faster, she added.
The meteoroid that produced the 1970 fireball once orbited the sun relatively close to the Earth, the team estimated. It probably didn’t come from the main asteroid belt between Mars and Jupiter, which is the source of many meteoroids, Dr. Gritsevich said.
Linking a meteorite to where it was born is important, said Marc Fries, a planetary scientist at NASA Johnson Space Center in Houston who was not involved in the research. “It goes from being just a rock you find on the ground to a rock that comes from a specific place in the solar system,” he said. To date, roughly 50 meteorites have had their orbits determined; Ischgl is the third-oldest of them.
The case of the Ischgl meteorite isn’t closed yet, 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 might have sat on Earth’s surface for far 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,” Dr. Brown said.
Even so, he said, there’s a neat story here: “It’s great to show that there’s value to this older data.”