Bright enough to outshine the Sun, people ran to windows to see the trail it left in the sky.<\/p>\n
A few minutes later, a boom swept through the town, shattering windows, bringing down walls and knocking people to the ground.<\/p>\n
That shocking sound was a meteor exploding overhead, but it wasn\u2019t just the noise. Fragments of rock were blasted across the landscape by the blast, falling down on the snow like rain.<\/p>\n
Videos from dashcams and CCTV cameras soon appeared on news channels around the world, sending meteorite hunters and researchers flocking to the town.<\/p>\n
Among those who arrived after the airblast was a young PhD student just getting started in her journalistic career \u2013 me.<\/p>\n
- History\u2019s most famous meteorites<\/strong><\/em><\/a><\/li>\n<\/ul>
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>BBC Sky at Night Magazine\u2019s Ezzy Pearson in Russia during filming for the 2013 documentary Meteor Strike! Fireball from Space. Credit: Ezzy Pearson<\/span><\/figcaption><\/div>\n I\u2019d been asked to present a documentary about the event with the rather dramatic title of Meteor Strike! Fireball from Space<\/i><\/span>, which was how a film crew and I found ourselves knee-deep in snow during the Russian winter, three weeks following the explosion.<\/p>\n
However, it was the very snow freezing my toes that made Chelyabinsk the perfect place for a meteorite hunt.<\/p>\n
When the rocks fell onto untouched snow, the heat they picked up from their journey through the atmosphere melted a clear, obvious hole.<\/p>\n
Find a hole, dig to the bottom and there\u2019s a good chance you\u2019ll find a meteorite.<\/p>\n
\n![\"""\"]( "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>A piece of the Chelyabinsk meteorite. Photo by Chip Somodevilla\/Getty Images<\/span><\/figcaption><\/div>\n The area had been picked over by the time we arrived, but our director did manage to find a 1cm wide pebble.<\/p>\n
It was pure black, covered in a fusion crust created by the heat of entry melting the surface.<\/p>\n
There\u2019s something magical about holding a freshly found meteorite in your hand.<\/p>\n
This was a fragment left over from the birth of the Solar System. It had been in space for billions of years until just a few weeks ago.<\/p>\n
And by this point, there was even a pretty good idea of where it had been.<\/p>\n
\u201cWhen a fireball is sighted in the sky, as was the case with Chelyabinsk, camera footage helps scientists to calculate where in space the rock might have originated \u2013 though this evidence isn\u2019t usually enough on its own to know for sure,\u201d says Natalie Starkey<\/a>, a geologist and author of Catching Stardust: Comets, Asteroids and the Birth of the Solar System<\/i><\/span>.\u00a0<\/span><\/p>\n
![\"""\"]( "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>The Chelyabinsk meteor was seen as a fireball, caught here on a car\u2019s dashboard camera. Image Credit: RIA NOVOSTI\/Science Photo Library<\/span><\/figcaption><\/div>\n Social media provided a wealth of camera footage, which planetary sleuths \u2013 both professional and amateur \u2013 had already set to work analysing, measuring the motion of the meteor and the shadows it cast, then comparing them to Google Maps.<\/p>\n
It appeared that the meteor had hit the atmosphere at a shallow angle, travelling around 65,000km\/h.<\/p>\n
Any large pieces that survived would have come down around nearby Lake Chebarkul \u2013 where an 8m-wide hole in the ice had already been found.<\/p>\n
Tracking the path back suggested that the meteor had probably been in an elliptical orbit, taking it from beyond Mars<\/a> to almost the orbit of Venus<\/a>, before striking our planet.<\/p>\n
![\"""\"]( "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>An 8m-wide hold in the ice of Chebarkul Lake, Chelyabinsk, thought to have been made by a fragment of the meteor that fell to Earth. Photo by Kyodo News Stills via Getty Images<\/span><\/figcaption><\/div>\n Another unusual source had recorded even more data: infrasound stations, which normally listen out for tests of illegal nuclear weapons, had picked up the explosion as far away as Antarctica.<\/p>\n
These measurements indicated that the blast, at 500 kilotons, was 30 times more powerful than the bomb detonated at Hiroshima, which allowed them to estimate that the asteroid<\/a> which struck the atmosphere had a mass of around 130,000 tonnes.\u00a0<\/span><\/span><\/p>\n
\u201cThat suggests the meteorite was around 20m in diameter, roughly the length of two double decker buses end-to-end. This is actually quite a small chunk of space rock, but it\u2019s still extremely lucky it broke up into smaller pieces,\u201d says Starkey.<\/p>\n
The infrasound recordings actually detected seven separate explosions, occurring between 83km and 30km in altitude.<\/p>\n
While making the documentary, I\u2019d discovered the reason for its repeated fractures first- hand when we arrived at the Ural Federal University in Yekaterinburg, a few hours\u2019 drive from Chelyabinsk.<\/p>\n
Their geologists had sent their own meteorite hunters to amass a sizable collection of meteorites, several of which had already been sliced up for closer examination.<\/p>\n
I didn\u2019t envy that task, as the rocks were remarkably fragile. Pieces crumbled off as you handled them, so it was no surprise the larger rock hadn\u2019t made it to the ground in one piece.<\/p>\n
![\"""\"]( "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>BBC Sky at Night Magazine\u2019s Dr Ezzy Pearson holds a 1kg sample of the meteorite. Credit: Ezzy Pearson<\/span><\/figcaption><\/div>\n \u201cOur atmosphere does a good job of slowing down space objects before they reach the surface of our planet,\u201d says Starkey.<\/p>\n
\u201cIt\u2019s not exactly like hitting a wall, but this deceleration results in the rock experiencing high temperatures and pressures, which can blow the meteor to pieces as all the heat and kinetic energy are released in an instant.\u201d<\/p>\n
Looking at the meteorite samples under an electron microscope revealed the Chelyabinsk meteor was an ordinary chondrite, the most common type of space rock found on Earth.<\/p>\n
These are stony meteorites made up of dust and grains called chondrules which were never incorporated into planets, meaning they represent the primal material from which the Solar System was built.<\/p>\n
Unfortunately, I only got a brief glimpse of the work being done before having to return home, but geologists around the world continued to study the rocks.<\/p>\n
On 16 October 2013, the collection got its biggest addition when a 540kg chunk was raised from Lake Chebarkul.<\/p>\n
In the years after, dozens of papers were released about the fireball, covering everything from the meteorite itself to the response of the emergency services.<\/p>\n
Together these built the picture of a space rock that had once been part of a larger asteroid in the asteroid belt<\/a> between Mars and Jupiter, but at some point had been chipped off and sent on its fateful journey towards Earth.<\/p>\n
Over time, the other falls were discovered and the Chelyabinsk meteorite samples became one of many in the catalogues (though my own small meteorite has always had pride of place on my desk).<\/p>\n
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Artist\u2019s impression of an asteroid belt. Credit: Maciej Frolow \/ Getty Images<\/span><\/figcaption><\/div>\n Yet there was still one outstanding, and niggling, question that researchers hadn\u2019t reached a satisfactory consensus about.<\/p>\n
When had the impacts that shattered the asteroid occurred?<\/p>\n
\u201cThere was a debate about whether there were dozens of impacts or just one,\u201d says Craig Walton from the University of Cambridge<\/a>.<\/p>\n
It was a debate that he has spent the last six years trying to resolve.\u00a0<\/span><\/p>\n
\u201cI first laid hands on the meteorite in 2016, when I did a summer research project at the Open University,\u201d says Walton.<\/p>\n
\u201cChelyabinsk is one of the oldest rocky objects in the Solar System. It\u2019s experienced a tumultuous history out in space and records a complicated history of collisions, but people hadn\u2019t revealed the exact sequence of events.\u201d<\/p>\n
This history is written in the dark veins that run through the Chelyabinsk meteorites.<\/p>\n
These are shock melts, created by the intense heat of a collision melting the rock unevenly, meaning the date of their origin shows when an impact occurred.<\/p>\n
Walton thought the key to their age might lie in the uranium within the melts.<\/p>\n
The element radioactively decays to lead, and while the rock is cool, both of these remain trapped in the crystal structure of the rock.<\/p>\n
When it\u2019s heated up, however, the lead escapes while the uranium stays put.<\/p>\n
\u201cBased on the fact that we know the half-life of uranium to lead, we can tell how long the crystal has been cold for by measuring the ratio of these two, essentially taking the time since it was last in an impact,\u201d says Walton.<\/p>\n
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<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>A Cathodoluminescence (CL) image of the Chelyabinsk meteorite, taken by a scanning electron microscope at a scale of several hundred micrometres, reveals crystals containing uranium and lead. Credit: University of Cambridge Department of Earth Sciences<\/span><\/figcaption><\/div>\n Getting the data, however, ended up taking six years, in part due to COVID-19 shutting down laboratories in the UK.\u00a0<\/span><\/p>\n
\u201cI ended up sending the precious samples I had spent years looking at to Beijing,\u201d says Walton. \u201cIt got impounded at customs for a month.\u201d<\/p>\n
Eventually the samples made it and the test results showed two distinct ages or events.<\/p>\n
The most recent impact, which chipped the asteroid from its parent rock and sent it towards Earth, appears to have occurred within the last few million years.<\/p>\n
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