Space rocks caused a meteorite | | forskning.se

On 22.27 November 7, the sky was lit for about three seconds over large parts of East Svealand. In the western part of Uppland, light was followed by a thunder-like explosion, then a lingering noise. Pictures and movie clips are spreading fast on social media. Erik Stimbles, an astronomer and meteorologist at Uppsala University, who had seen and heard the phenomenon himself, was able shortly thereafter, with the help of his colleagues in Norway, to determine that a large space rock, also called a rocky, had fallen to Earth.

Eric Stimples explains what’s going on:

Space rocks fall on Earth at a very high speed, reaching several tens of kilometers per second. When the stone meets the earth’s atmosphere, the stone slows down and the air surrounding the stone begins to glow, which leads to the appearance of light phenomenon. The heat that creates melts the surface and the usual thing is that a space stone melts completely. If the stone is large enough, fragments can survive the violent flight through the atmosphere. The remains can then be found on Earth in the form of meteors. The thunder-like sound and noise is caused by the supersonic speed of the space stone.

The solid matter observed on November 7, 2020, caused a meteorite fall. Small bits of a dark-colored meteor crust were found. The fragments are about 3 millimeters in size. Photo: Swedish Museum of Natural History.

Since 2013, a network of cameras has existed in Sweden that measures meteorite trajectories in the sky. The network records many small meteors resulting from dust the size of grains of sand that burns into the atmosphere, in some cases several dozen per night. But about ten times a year, bright meteors, also called fireballs, are observed that need more accurate measurement. On a few occasions in recent years, there has been a suspicion of a meteor falling in Sweden, but nothing as bright and promising as the phenomenon of light on November 7. However, it was cloudy in Uppland, so none of the Swedish cameras noticed this phenomenon.

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Meteor notes and meteor discoveries are very interesting. The observations tell us exactly from which direction and at what speed space rocks collided with the Earth. By counting back, it is then possible to find out which part of the Solar System the body originated from. Most commonly, it comes from collisions between asteroids in the region between the planets of Mars and Jupiter. If you find a meteorite after a space rock, it can tell you what the early Solar System looked like. Meteorites could be as old as our Solar System, about 4.6 billion years ago, much older than rocks on Earth.

Calculations led to results

Just like in Sweden, there are camera networks in neighboring countries that measure meteor trajectories in the sky. Meteor camera stations in Norway, Finland and Denmark captured the event on November 7 in a photo. With the help of colleagues in neighboring countries, Eric Stimples, a researcher at Uppsala University, calculated this approach. Calculations showed that the stone entered the atmosphere in a steep path and had a very large mass of about nine tons. The combination of injury speed and large mass meant that the glowing stone could be observed at an unusually low altitude, about 17 km. This made it very likely that the phenomenon was a true meteor fall. Camera observations made it possible to locate a very interesting area near the village of Odalin, north of Fjärdhundra in the municipality of Enköping. The area consists of fields and forests and has been researched by a large group of interested parties.

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Despite initially high activity, no results were reported. But on November 22, following the advice of meteorite collectors, Jürgen Langov, a mineralogist at the Swedish Museum of Natural History, found suspicious fragments in the designated area. Metal parts are black in color and range in size from 1 to 6 millimeters. The fragments have now been examined at the Swedish Museum of Natural History, and researchers state that it was an iron meteorite. This is unusual, as 95% of meteorite cases are stony meteors. It is also the first discovery after an observed meteorite strike for 66 years in Sweden.

The meteorite takes root

A few meters from where the fragments were found, there is a large boulder covered with moss and lichens with clear signs that they were hit by something heavy.

The stone has a large mark as if it was struck with a sledgehammer. Next to the ground, there was a larger pit with a rejected tree root, says Jürgen Langov, a mineralogist at the Swedish Museum of Natural History.

The cause of the crater may have been a fist-sized meteorite. With the help of a magnet, the Earth can be “sucked” out of the magnetic particles. This is how the scattered shards were found lying on top of moss up to ten meters from the stone with the mark. Despite numerous search efforts in the following weeks, unfortunately no fist-sized meteor was found.

Preliminary chemical analysis of the found fragments can confirm that it was an iron meteorite. In addition to a lot of iron, the sample contains about ten percent nickel, which is characteristic of iron meteorites.

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We need more material from the meteorite to fully characterize it and give it a name, says Dan Holtstamm, mineralogist and collections director at the Swedish Museum of Natural History. The fragments examined now form only parts of the iron meteorite crust, which have been affected by melting during the violent slowdown in the atmosphere.

Search efforts continue after the winter break when the ground is free of snow. It’s entirely possible that more meteor fragments remain in the area. The Swedish Museum of Natural History and Uppsala University each request information on interesting discoveries in the area around Udalen.

call:

Eric Stempels, Astronomer in the Department of Physics and Astronomy at Uppsala University, [email protected]
Jürgen Langoff, Mineralogist at the Swedish Museum of Natural History, [email protected]
Dan Holtstam, mineralogist and director of collections at the Swedish Museum of Natural History, [email protected]

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