Tens of thousands of meteorites have been found on Earth, but the vast majority remain shrouded in mystery. Of course, these rocks come from space, but determining their exact origin, in the solar system or even beyond, is difficult without knowing their flight paths.
But now scientists believe they have linked a meteorite discovered in the Austrian Alps decades ago to bright flashes of light from a space rock hurtling through our planet’s atmosphere. It’s rare to connect a meteorite to its parent “fireball,” and these results demonstrate 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, 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 back to his house and placed it in the box.
Thirty-two years later, Mr. Pfefferle heard the news of a meteorite discovered in Austria and wondered if his strange stone was also from outer space. He decided to bring his stone to the university for analysis.
Mr. Pfefferle’s find turned out to be a fairly large meteorite, at over two pounds. Moreover, its unweathered exterior suggested that it had fallen to Earth only a short time 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 thought that if the Ischgl meteorite fell to Earth relatively recently, its arrival may have been caught on film. A network of 25 sky-watching cameras spread across southern Germany has been collecting long-exposure images of the night sky since 1966. By the time the network shuts down in 2022, it has recorded over 2,000 fireballs.
“It made the most sense to trace it back to the last fireball we saw in the area,” said Dr. Gritsevich.
She and her team searched for negatives of images containing fireballs stored at the German Aerospace Center in Augsburg. After digitizing the images, scientists estimated various parameters about the incoming meteors, such as their masses, shapes, speeds and angles of entry. Using this data, the researchers focused on a dozen events most likely to have produced large meteorites. Only three occurred before 1976.
The team reconstructed the trajectory of each of these three fireballs and calculated where the meteorites were most likely to be found. There was only one match where the Ischgl meteorite was found. This led scientists to conclude that the fireball that swept low over the horizon in the early morning hours of November 24, 1970 gave birth to the Ischgl meteorite.
“This one fit the bill exactly,” said Dr. Gritsevich.
She and her colleagues calculated that the incoming meteor struck Earth at roughly 45,000 miles per hour. That’s fast, but within the range of meteoroids born in the Solar System, said Dr. Gritsevich. On the other hand, something that came from outside the solar system would travel much faster, she added.
The meteoroid that created the fireball in 1970 once orbited the Sun relatively close to Earth, the team estimated. It probably does not come from the main asteroid belt between Mars and Jupiter, which is the source of many meteoroids, said Dr. Gritsevich.
Connecting the 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 a rock you find on earth 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.
However, the case for the Ischgl meteorite 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 sat on Earth’s surface for much longer than six years. The high mountain environment it fell into may well have preserved the rock.
“It really could have been there for decades and potentially centuries,” said Dr. Brown.
Still, he said, there’s a nice story here: “It’s great to show that this older data has value.”