Science

A strange stone in a box is linked to a shooting star that fell 54 years ago

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 it is difficult to determine their exact origins, in the solar system or even beyond, without knowing their flight paths.

But now, researchers think they’ve connected 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 to connect a meteorite to its parent “fireball,” and these results show the value of combing through old datasets, 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 rock back to his house and put it in a box.

Thirty-two years later, Mr. Pfefferle heard a news report about a meteorite discovered in Austria and wondered if his strange rock might also have come from space. He decided to take his stone to a university to be analyzed.

Mr. Pfefferle’s find turned out to be a meteorite, and at more than two pounds, a relatively large one. Furthermore, its unweathered exterior suggested that it had only fallen to Earth 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 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-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 made the most sense to trace it back to the most recent fireball seen in the area,” Dr. Gritsevich said.

She and her team searched for 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 impact. Using that data, the researchers zeroed in on a dozen events that were most likely to have produced significant meteorites. Only three had occurred before 1976.

The team reconstructed the trajectory of each of those three fireballs and calculated where meteorites were most likely to be found. There was only one match to the spot where the Ischgl meteorite was found. This led the researchers to conclude that the fireball that arced low over the horizon in the early morning hours of November 24, 1970, was the birth of the Ischgl meteorite.

“This one matched exactly,” said Dr. Gritsevich.

She and her colleagues calculated that the incoming meteor fell to Earth at a speed of about 70,000 kilometers per hour. That’s fast, but well within the range of meteoroids born in the solar system, said Dr. Gritsevich. In contrast, something coming from outside the solar system would have traveled much faster, she added.

The meteoroid that produced the fireball in 1970 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, said Dr. Gritsevich.

It’s important to tie a meteorite to the place where it was born, said Marc Fries, a planetary scientist at NASA Johnson Space Center in Houston who was not involved in the research. “It goes from 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.

The case of 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 study. He said there is always a possibility that this meteorite was on Earth’s surface for much longer than six years. The alpine environment where it fell would have preserved the rock well.

“It really could have been there for decades and possibly even centuries,” said Dr. Brown.

Still, he says there is a nice story behind it: “It’s great to show that there is value in this older data.”

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