Tens of thousands of meteorites have been found on Earth, but the vast majority remain shrouded in mystery. These rocks obviously come from space, but pinpointing their exact origin, in the solar system or beyond, is difficult without knowing their flight paths.
But researchers now 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 with its parent “fireball,” and these findings demonstrate the utility of comparing 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 remains of an avalanche near the Austrian village of Ischgl when he noticed a strange-looking rock. He took the fist-sized black stone 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 whether his strange rock might also have come from space. He decided to take his rock to a university to be analyzed.
Mr. Pfefferle's find turned out to be a meteorite, and, weighing more than a pound, a relatively large one. Furthermore, its pristine exterior suggested that it had fallen to Earth only shortly before Mr. Pfefferle picked it up.
“It was such a cool 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 hypothesized that if the Ischgl meteorite had fallen to Earth relatively recently, perhaps its arrival would have 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 ceased operations in 2022, it had recorded more than 2,000 fireballs.
“It was logical to trace it back to the most recent fireball seen in the area,” Dr. Gritsevich said.
She and her team hunted down image negatives containing fireballs stored at the German Aerospace Center in Augsburg. After digitizing the images, the researchers estimated various parameters related to the incoming meteors, such as their masses, shapes, speeds and entry angles. Using this data, the researchers identified a dozen events that most likely produced sizable meteorites. Before 1976 only three had occurred.
The team reconstructed the trajectory of each of those three fireballs and calculated where the meteorites would most likely be found. There was only one match to the location where the Ischgl meteorite was recovered. This led researchers to conclude that the fireball that crossed the horizon in the early morning hours of November 24, 1970 gave birth to the Ischgl meteorite.
“This matched exactly,” Dr. Gritsevich said.
She and her colleagues calculated that the incoming meteor hit Earth at a speed of about 45,000 miles per hour. This is fast but well within the range of meteoroids born in the solar system, Dr. Gritsevich said. Something from beyond the solar system, however, would have traveled much faster, he added.
The meteoroid that produced the 1970 fireball once orbited the sun relatively close to 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's Johnson Space Center in Houston who was not involved in the research. “It goes from just being a rock that you find on the ground to a rock that comes from a specific place in the solar system,” he said. To date, the orbits of approximately 50 meteorites have been determined; Ischgl is the third oldest of them.
The case of the Ischgl meteorite, however, is not yet closed, 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 could have remained on the Earth's surface for much longer than six years. The alpine environment in which it fell may 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 good story here: “It's nice to show that there's value in this older data.”