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Met Name

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  L/LL 4

TKW 330 kg. Observed fall March 12, 1899, near Borgå, Nyland, Finland.

 

Steve writes:

At 9:30 PM Finnish time on March 12th 1899 (not 10:30 PM, as mistakenly published in Germany in 1902), a huge meteorite created a 12-foot hole in a foot of ice, then burrowed over 20 feet deep into the mud at the bottom of a shallow bay near the Uusimaa region’s small inland town of Bjurböle, just south of Porvoo (Porvoo is 50 km east of Helsinki near the Baltic Sea). It was so bright that witnesses reported sightings as far away as Stockholm, St. Petersburg, and Byelorussia.

The fireball momentarily turned the night sky into day and produced a roar so loud that buildings shook and people ran panicked out into the streets, fearing it was heavy artillery fire in Viipuri (a frontier town between Finland and Russia). The event was so impressive that it headlined the area’s leading newspapers for almost a week, with descriptions the next day immediately identifying it as a meteorite. And because of the number of eyewitnesses, its trajectory was estimated well enough to find it just two days after that.

Because Bjurböle entered our atmosphere at just the right angle, it didn’t explode during its passage through our atmosphere like so many other meteorites often do; the roar heard by witnesses was actually sonic booms as the meteorite fragmented and pieces flew at supersonic speeds over Helsinki towards Porvoo and Bjurböle. Recovered pieces were spread over a 75- by 100-foot area and totaled around 330 kilograms, giving rise to an estimated weight of over 400 kilograms when it hit. Surprisingly, the main mass weighs 79 kilograms – amazing given the meteorite is so friable that it will literally crumble when handled.

The Bjurböle meteorite was well known throughout much of Europe at the time, and it was the centerpiece at the Finnish pavilion of the 1900 Paris World Exhibition. But few knew that the original main mass never left Finland – local officials were so concerned about possible damage or theft during transport or while on display that they created and sent instead a nearly exact replica, with the original kept secretly safe at Helsinki University, where it remains to this day.

Bjurböle is a rare L/LL4 chondrite – as of this writing, one of only 21, and one of only 12 meteorites of any type found in Finland. It has very little metal but abundant, fairly large chondrules that show evidence of metamorphosis that homogenized the olivine compositions and recrystallized the fine-grained matrix. Japan’s Hayabusa space probe found asteroid 25143-Itokawa’s mineral composition to be chemically similar to Bjurböle’s; other studies suggested Bjurböle formed about 110 million years before Earth.

The 1.93 gram piece pictured in this post was acquired not long after I started collecting meteorites. The pictures are from that era, but the fragment is buried somewhere in our safe under a few hundred other meteorites, so unfortunately I wasn’t able to dig it out to take better ones in time for this almost anniversary post (Bjurböle fell on the same day of the year as Lowicz). The piece measures roughly 8x8x16 mm.