Iron from the sky

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Michael D Johnson

It has now been 63 years since a huge iron meteorite impacted the Sikhote-Alin Mountains of the former USSR. Imagine what it must have been like on that cold morning of 12 February 1947 – the tremendous smoke trail, the thunderous crash and the roaring sound it made, as the fireball descended to Earth …

The local time was 10:38am and the sky was clear. The fireball, travelling at more than 49,900km per hour started to fragment in the Earth’s atmosphere at an altitude of 6km. The bright, blinding fireball streaked across the sky and left an enormous trail of fire and smoke that was visible for hours. Eyewitnesses described it as being brighter than the sun. The meteorite was travelling at a speed of about 14km per second as it entered the atmosphere, at which point it began to break apart, with the fragments continuing to fall together. At an altitude of around 5.6km, the largest apparently broke up in a violent explosion.

Not long after the fireball disappeared, thunderous explosions were heard followed by a load crash that was felt for miles. It is estimated that more than 23,000kg fell that morning. The impact made over 120 craters of varying sizes and is the largest observed meteorite fall in history.

In the town of Iman, a local artist, by the name of PJ Medvedev, was at home painting. As the event captured his attention, he immediately started creating a picture while it was still fresh in his mind (Fig.1). This was reproduced on a 1957 Russian postage stamp commemorating the 10th anniversary of the event.

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Fig. 1: Replica of the painting that hangs over a 10.4kg Sikhote-Alin individual in the author’s showroom.

As the meteorite fell in the daytime, it was observed by many eyewitnesses. Observational data was turned over to VG Fesenkov, chairman of the meteorite committee of the USSR Academy of Science. Fesenkov was able to estimate the meteorite’s orbit before it encountered the Earth. This had an elliptical shape, with its greatest point of distance from the sun situated within the asteroid belt, which is a similar trajectory to those of many other small bodies crossing the orbit of the Earth. This was probably created by collisions within the asteroid belt.

Sikhote-Alin was a massive fall. The overall size of the meteorite has been estimated at 100,000kg. Yevgeny Krinov, a geologist and renowned meteorite researcher from Russia during the twentieth century, estimated the post atmospheric mass of the meteorite at some 70,000kg. The meteorite-strewn field covered an elliptical area of about 1.3km, with some of the fragments making craters, the largest of which was about 26m across and 6m deep. Some fragments of the meteorite were even blasted into the surrounding trees.

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Fig. 2: A large, oriented individual with countless flow lines and many regmaglypts.

The fall created two types of specimens:

  • The first consist of pieces showing ablation, in which the crust probably broke off the main mass early in the descent. These pieces are characterised by smooth regmaglypts (that is, cavities resembling thumb prints) on the surface.
  • The second type consists of shrapnel pieces that are sharp and jagged. These were either torn apart during the atmospheric explosions or blasted apart upon impact on the frozen ground. Most were probably the result of the explosion at 5.6km altitude.
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Fig.3: A large, oriented individual with flow lines, roll over rim.

Growing up in a small town in Boiling Springs, South Carolina, USA, I have always been an avid sky watcher. I would spend many hours of the night watching meteor showers, thinking to myself what it must be like to hold one of these cosmic wonders in my hand. Not until many years later, while browsing the Internet, did I realise that you could actually purchase and even find these natural wonders from the cosmos.

One my favourite specimens from the Sikhote-Alin event is a 6,200g individual with beautiful fusion crust, thumb-printing and flow lines (Fig. 4).

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Fig. 4: A large, premium S-A individual – one of the author’s favourites.

To most collectors, these meteorites are what most people imagine a rock from outer space should look like. They develop several thumbprints and flow lines, due to the heating and ablation they experience during entry through the Earth’s atmosphere. Indeed, some are described as ‘oriented’ (Fig. 5). That is, during their flight through the atmosphere, the leading edge maintains a fixed orientation towards our planet, resulting in a dome or bullet shape, which is typical of highly oriented meteorites.

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Fig. 5: Flight-oriented Sikhote-Alin iron individual with flow lines radiating around the edges.

Sikhote-Alin Iron Meteorites are the easiest to recognise of all meteorites, but only one in ten meteorites that fall from space is iron. These type meteorite specimens are composed of the following: 5.8% nickel, 0.42% cobalt, 0.46% phosphorus, 0.28% sulphur, 52 parts per million (ppm) gallium, 16 ppm germanium, and 0.03 ppm iridium. The remaining volume is iron.

As a result of my interest in iron meteorites, I am now known as ‘Iron Man’ to most. I have a continuing obsession with finding more samples from the Sikhote-Alin fall as I really do think this is one of the most important in history, next to the Allende stone meteorite that fell in New Mexico in 1969. I have many collectors and hunters of rocks from space visit my growing collection of iron meteorites. This is definitely the best job in the Universe and, over the years, I have bought, sold or traded almost a million dollars worth of rocks from space.

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Fig. 6: A Sikhote-Alin individual with a naturally formed hole. Some meteorites even form the shapes of human heads. This one bares the resemblance of Bart Simpson from the The Simpsons!

What is more fascinating than holding a rock from space that has travelled all the way from the asteroid belt to your home? As I always say, “You don’t have to go to outer space – they come to you. It’s like Heaven on Earth!”
 
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