Benešov
A fireball photographed over the Czech Republic in 1991 whose meteorites were found only 20 years later – and turned out to be a mixture of types.
Key facts
- Type
- Ordinary chondrites (LL and H types) in one meteoroid
- Fell or found
- Fell (photographed in 1991; found in 2011)
- Year
- 1991 (7 May)
- Country
- Czech Republic
- Mass
- a few small fragments
- Official name
- Benešov
On the night of 7 May 1991, an extremely bright fireball blazed across the sky over Central Bohemia in what was then Czechoslovakia. It was photographed by cameras of the European Fireball Network, a system of automatic all-sky cameras that has been watching for bright meteors over Central Europe since the 1960s. The images were superb, and scientists used them to calculate the fireball's path through the atmosphere and its orbit around the Sun. They also predicted that meteorites might have fallen near the town of Benešov, south-east of Prague.
A search that failed, then succeeded
In 1991 searches were made in the predicted area, but no meteorites were found. For years the Benešov fireball was a famous example of a well-recorded fall that had apparently left nothing behind.
Then, about 20 years later, Pavel Spurný and his colleagues at the Astronomical Institute of the Czech Academy of Sciences re-analysed the original records with improved methods. They realised that the meteoroid had broken up in a complex way and that some fragments might have landed in a different place from the one originally searched. In 2011 a new search in the revised area finally found small meteorite fragments, some two decades after the fall.
A surprising mixture
When the fragments were studied, scientists found that they were not all of the same type. The finds included LL chondrite material, from a group of ordinary chondrites low in iron and metal, a fragment of H chondrite, a group rich in metal, and a fragment reported to be of a different kind again. This means that the Benešov meteoroid was a mixture of different materials, a breccia containing fragments from more than one parent body, joined together by collisions in space.
This was an important discovery. It showed that some meteoroids are not uniform rocks but jumbles of different types, similar to what was found with the asteroid 2008 TC3 and the Almahata Sitta meteorites in Sudan. Such mixtures affect how meteoroids break up in the atmosphere, because different materials have different strengths.
Benešov also taught searchers a practical lesson. Fragments from a complicated break-up can be widely scattered, and small stones can lie for years in fields and woodland without being noticed, especially in a landscape very different from an open desert. Careful modelling of how each fragment was slowed by the air proved to be the key to finding them.
The European Fireball Network
The Benešov story highlights the value of long-running camera networks. The European Fireball Network grew out of work in Czechoslovakia that led to the first photographed meteorite fall with a calculated orbit: the Příbram meteorite of 1959. Since then, the network has expanded and modernised, and it has been involved in the recovery of several meteorites with known orbits.
By photographing fireballs from more than one station, scientists can measure their paths precisely. That allows them to calculate where meteorites might have fallen and where in the Solar System the meteoroids came from.
Why it matters
Benešov shows that patience and better analysis can pay off. A meteorite fall that seemed to have produced nothing turned out, decades later, to have left fragments on the ground, and those fragments revealed a mixed meteoroid that taught scientists something new.
It also shows how meteorite science depends on combining observations from the sky with careful searches on the ground. Photographs, calculations, field teams and laboratory studies all play their part.
If you're interested in fireballs, you can help too. Report any bright fireball you see, with the time, direction and duration, to a fireball network or astronomy society. Searching for meteorites should always be done with landowners' permission and in line with local laws.
Did you know?
The Benešov fireball was photographed in 1991, but its meteorites were not found until 2011.
The fragments include more than one type of chondrite, showing the meteoroid was a mixture.
The European Fireball Network grew from work that recorded the Příbram fall of 1959, the first meteorite with a photographically calculated orbit.