tag:theconversation.com,2011:/uk/topics/chelyabinsk-7776/articlesChelyabinsk – The Conversation2016-03-02T14:41:48Ztag:theconversation.com,2011:article/556732016-03-02T14:41:48Z2016-03-02T14:41:48ZGreat balls of fire: the truth about Scotland’s mysterious flash of light<figure><img src="https://images.theconversation.com/files/113566/original/image-20160302-25912-1dixs47.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">On February 29, night suddenly becomes day</span> </figcaption></figure><p>On Monday February 29 around 18:45, many lucky people in Scotland and the north of England witnessed something spectacular. A bright light streamed across the sky, flashing several times before fading away. You could see it as far north as Shetland and Orkney, and as far south as Newcastle. Many people posted their camera recordings online, allowing millions to see it around the world.</p>
<p>Was it a <a href="http://www.ufosightingsdaily.com/2016/03/meteor-or-ufo-seen-over-scotland-on-feb.html">UFO</a>? Was it a piece of high-tech military technology? No and no. This was a rock from space colliding with the Earth’s atmosphere. The solar system is full of this kind of debris: bits of rock and ice left over from the formation of the planets some five billion years ago, or chipped off asteroids during more recent collisions in space. The Earth encounters and sweeps up this debris all the time. </p>
<p>Most common are the small specks up to the size of a grain of sand that produce brief flashes of light – a shooting star or meteor – when they encounter the Earth’s atmosphere and burn up. If you stand outside and watch the sky on a clear dark night, you should be able to spot several of these every hour. If you’re really lucky you might see a meteor shower, when the Earth is moving through the path of a comet that has left a trail of dust and rock behind after its icy material has been evaporated away by the sun’s heat.</p>
<h2>Fireball February</h2>
<p>When larger pieces of space debris such as the Scottish one stray into the Earth’s atmosphere, they produce more spectacular meteors as they burn up. These are known as fireballs or “bolides”. Judging from the footage online, Scotland witnessed one of about 10cm in diameter. It will have been moving at roughly 30km/second, burning up from the friction with the air as it plunged through. Some of the recordings show it breaking into dozens of smaller pieces before finally fading away. Sometimes this can produce meteorites – bits of rock that manage to survive their fiery descent and hit the ground – but apparently not in this case. </p>
<p>After the meteor flash, some people heard a bang or rumbling sounds. That would have been a <a href="http://www.physlink.com/Education/AskExperts/ae53.cfm">sonic boom</a>, like that produced by a plane that breaks the sound barrier. One report on the web says the sound <a href="http://www.bbc.co.uk/news/uk-scotland-north-east-orkney-shetland-35689551">was heard</a> 90 seconds after the flash. If so, the meteor was 18 miles away, since sound travels about one mile every five seconds in air. Just like with the thunder after a lightning strike, you can estimate the distance of these things by counting the seconds of the interval and dividing by five. </p>
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<p>This spectacular show was a special treat, only occurring a few times a year anywhere on the planet. In my whole life I’ve seen just one that was brighter, about 30 years ago in California’s Mohave desert, where I had travelled to photograph a comet. I remember bending down to pick something off the ground when everything lit up in daylight colours. I was stunned for a few seconds before turning around to see the remaining pieces of that fireball streaming across the sky.</p>
<h2>When to worry</h2>
<p>The meteor over Scotland was a brief and beautiful sight, fortunately not dangerous, but much larger space rocks can be devastating. On February 15 2013 a meteor with a diameter of 20 metres was recorded crossing the sky in Chelyabinsk, central Russia. The explosion and shockwave was serious enough to blast windows out of buildings. Many people were seriously injured, cut by flying glass (if ever you see an unexpected bright flash outside your window, move away from the glass just in case).</p>
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<p>An event like this may occur every few decades. The largest impact in recorded history, the <a href="http://science.nasa.gov/science-news/science-at-nasa/2008/30jun_tunguska/">Tunguska event</a> of 1908, flattened forests in Siberia for 100 miles. Even larger impacts can bring global catastrophe. Some 60 million years ago, in what is now the Yucatan peninsula in Mexico, an impact <a href="http://www.universetoday.com/36697/the-asteroid-that-killed-the-dinosaurs/">made a crater</a> 100 miles across. It launched huge tsunamis, covered the entire planet with debris, darkened the skies enough to change the climate for years, and is thought to have caused or hastened the extinction of the dinosaurs (except for those that survive as birds). </p>
<p>Astronomers are now searching the skies for faint moving objects that cross the Earth’s orbit and could in future cause a regional or global catastrophe. If we can spot these far enough in advance, we may be able to intercept the object with a space probe to nudge its orbit enough to make it miss the Earth. Which would be for the best.</p><img src="https://counter.theconversation.com/content/55673/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Keith Horne does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Was it a UFO? Was it a high-tech plane? Here’s what lucky people really saw over Scotland on February 29.Keith Horne, Professor of Astronomy, University of St AndrewsLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/554542016-02-26T11:53:51Z2016-02-26T11:53:51ZThe five greatest balls of fire over Earth<figure><img src="https://images.theconversation.com/files/113040/original/image-20160226-26723-1atn4q.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Chelyabinsk meteor.</span> <span class="attribution"><span class="source">Nikita Plekhanov/wikimedia</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>We live on a moving target in a cosmic firing range. Each day, the Earth is bombarded by about a hundred tonnes of space debris. It may sound alarming, but this is really nothing to worry about. Most of the objects that fall towards our planet are pretty small – typically about the size of a grain of sand or even smaller – and burn up in the upper atmosphere tens of kilometres above the ground. </p>
<p>But every now and again, something much bigger plummets Earthward and blazes a trail across the sky. Some make the headlines whereas others arrive almost unnoticed. Here are the most interesting movers and shakers.</p>
<h2>1. South Atlantic meteor</h2>
<p>On February 6, a chunk of interplanetary rubble, probably made of rock and measuring roughly five metres across, <a href="http://www.independent.co.uk/news/science/huge-fireball-explodes-over-atlantic-as-meteor-flies-into-earth-from-space-a6892921.html">entered the Earth’s upper atmosphere</a>. Hurtling across the sky at tens of kilometres a second, the air ahead of the meteor was compressed and heated, vaporising the object as it penetrated deep into the atmosphere. At some point, as the meteor streaked 20-30km above the South Atlantic ocean, it exploded with about the same force as <a href="http://www.iflscience.com/space/largest-meteor-years-fell-over-atlantic">12,000 tonnes of TNT</a> (about the same explosive force as the atomic bomb dropped on the Japanese city of Hiroshima). </p>
<p>Oddly enough, nobody saw this meteor explosion. We only know about it because of measurements made by various defence and scientific facilities that recorded the resulting atmospheric disturbances. The Earth is mainly ocean and uninhabited land and the odds are that most meteors burn up like this one, without any witnesses.</p>
<h2>2. Chelyabinsk meteor</h2>
<p>In contrast, some meteors grab worldwide attention. This fireball <a href="https://theconversation.com/secrets-revealed-of-dash-cam-meteorite-that-rocked-russia-19923">tore across the dawn skies</a> over Chelyabinsk, Russia, on February 15 2013. Moving at around 20km a second, the fireball was many times brighter than the sun and was captured by car dashboard, CCTV and mobile phone cameras across the region.</p>
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<p>Estimates indicate that object was about 20 metres across and exploded with the force of <a href="http://earthsky.org/space/largest-fireball-since-chelyabinsk-falls-over-atlantic">500,000 tonnes of TNT</a>, shattering thousands of windows, leaving a trail of damage 55 miles on either side of the rock’s trajectory and causing injuries to over 1,200 residents in the region. Although this object exploded in the atmosphere, the Chelyabinsk meteor hinted at the damage that an airburst can inflict on a populated area. </p>
<h2>3. 2008 TC3</h2>
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<img alt="" src="https://images.theconversation.com/files/113043/original/image-20160226-26687-d82h4z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/113043/original/image-20160226-26687-d82h4z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/113043/original/image-20160226-26687-d82h4z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/113043/original/image-20160226-26687-d82h4z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/113043/original/image-20160226-26687-d82h4z.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/113043/original/image-20160226-26687-d82h4z.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/113043/original/image-20160226-26687-d82h4z.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">TC3 fragment found on February 28, 2009.</span>
<span class="attribution"><span class="source">NASA / SETI / P. Jenniskens</span></span>
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<p>This four-metre diameter object, weighing in around 80 tonnes, <a href="http://www.planetary.org/blogs/emily-lakdawalla/2008/1684.html">entered Earth’s atmosphere over northern Sudan</a> on the morning of October 7 2008. Moving at about 13km a second, the meteor exploded tens of kilometres above the ground with a force of about 1,000 tonnes of TNT, lighting up the dawn sky as a fireball that was observed over 1,000 kilometres away. </p>
<p>Although not particularly well-known, 2008 TC3 was a notable first – it was the first object to be observed and tracked prior to reaching Earth. This means it provided a much-needed test of the process of detecting and tracking near-Earth objects. Other incoming meteors have been detected since, but the process is not infallible. For example, the much bigger Chelyabinsk meteor remained undetected until its arrival in the skies over Russia.</p>
<h2>4. Tunguska event</h2>
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<span class="caption">Trees knocked over by the Tunguska blast.</span>
<span class="attribution"><span class="source">Leonid Kulik/wikimedia</span></span>
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<p>This was a <a href="https://theconversation.com/mystery-solved-meteorite-caused-tunguska-devastation-15154">devastating event</a>. On the morning of June 30 1908 an explosion over a sparsely-populated region of eastern Siberia flattened 80m trees over an area of two thousand square kilometres of forest. Subsequent analysis of the explosion suggests that it packed the same punch as around <a href="http://news.bbc.co.uk/1/hi/sci/tech/1628806.stm">15 megatonnes of TNT</a> – more than a thousand times the power of the Hiroshima bomb. </p>
<p>Estimates of the size and speed of the meteor depend on assumptions about the composition of the object: rocky and icy meteoroids have differ densities and behave differently during their descent. Nevertheless, the object responsible for the Tunguska blast is thought to have been between <a href="http://www.astrobio.net/topic/solar-system/meteoritescomets-and-asteroids/spaceguard-five-years/">50-200 metres in diameter</a>, exploding 5-10km above the ground. The blast generated seismic and atmospheric disturbance across Asia and Europe but, amazingly, did not result in any known casualties.</p>
<h2>5. Barringer Crater</h2>
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<span class="caption">Barringer Crater aerial photo.</span>
<span class="attribution"><span class="source">USGS/wikimedia</span></span>
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<p>This 1,200 metre wide, 170-metre deep scar in Arizona’s desert landscape is testament to what happens when a meteor survives its journey through the atmosphere and <a href="https://theconversation.com/meteorite-impact-turns-silica-into-stishovite-in-a-billionth-of-a-second-48946">impacts onto the Earth’s surface</a>. Modelling suggest that the crater was created by a nickel-iron meteorite about 50 metres in diameter impacting the surface at around 13km a second with a force of 10 megatonnes of TNT. </p>
<p>Although not very different in size and velocity to the object associated with the Tunguska event, a steeper descent or differences in composition meant that the Barringer meteorite did not disintegrate or explode in the atmosphere. Fortunately, the impact occurred around 50,000 years ago, when the region was uninhabited by humans, but it is a stark reminder of the destructive power that can be unleashed when the heavens fall.</p><img src="https://counter.theconversation.com/content/55454/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jim Wild receives funding from the Science and Technology Facilities Council and the Natural Environment Research Council. He is also the vice-President (Geophysics) of the Royal Astronomical Society. He occasionally works with a variety of UK-based travel and tourism companies to engage relevant audiences on topics related to his research.</span></em></p>A meteor exploding over the South Pacific on February 6 was the biggest since the Chelyabinsk meteor in 2013. Here are some other fiery visitors.Jim Wild, Professor of Space Physics, Lancaster UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/199232013-11-06T18:03:27Z2013-11-06T18:03:27ZSecrets revealed of ‘dash-cam’ meteorite that rocked Russia<figure><img src="https://images.theconversation.com/files/34557/original/dg69ck4r-1383757496.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The trail of a meteor that caused some harm, but mostly helped humanity understand the meteorite strikes on Earth.</span> <span class="attribution"><span class="source">alexeya</span></span></figcaption></figure><figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/34557/original/dg69ck4r-1383757496.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/34557/original/dg69ck4r-1383757496.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=325&fit=crop&dpr=1 600w, https://images.theconversation.com/files/34557/original/dg69ck4r-1383757496.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=325&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/34557/original/dg69ck4r-1383757496.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=325&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/34557/original/dg69ck4r-1383757496.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=408&fit=crop&dpr=1 754w, https://images.theconversation.com/files/34557/original/dg69ck4r-1383757496.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=408&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/34557/original/dg69ck4r-1383757496.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=408&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">Is it a bird, is it a plane?</span>
<span class="attribution"><span class="source">alexeya</span></span>
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<p>The asteroid impact that burst over Chelyabinsk, Russia, on the morning of February 15 has provided a huge collection of new data that scientists have been analysing since. This week, three papers, two in Nature and one in Science, describe new aspects of the meteorite’s airburst, building the most-detailed forensic picture of the events of that morning.</p>
<p>First reports of the Chelyabinsk airburst came from a plethora of dash-cams that caught the event. For the first time, a meteorite impact was recorded widely on camera, a consequence of technological advance and (presumably) increasingly litigious or bad Russian drivers. Alongside the dash-cam recordings, the fireball and the transient shadow that it cast was recorded across the region by fixed CCTV cameras. And looking back at Earth from space, the trajectory of the fireball was observed in <a href="http://www.space.com/23273-russia-meteor-chelyabinsk-satellite-photos.html">satellite imagery</a>.</p>
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<p>The brightness of the fireball has provided an estimate of the energy of the airburst, equivalent to an explosion of more than 500 kilotons of TNT, many times greater than the Hiroshima atomic bomb. Similar estimates of the size of the explosion were obtained earlier this year from the array of infrasound detectors operated by the Comprehensive Nuclear Test Ban Treaty Organization, which maintains an array of nuclear bomb monitoring equipment.</p>
<p>The new papers exploit an even wider array of data. Much of the information is, effectively, a superb example of crowdsourced science: damage reports, surveys of damage, injury reports, camera recordings and other data have provided an unprecedented set of measurements of the event, as reported in <a href="http://dx.doi.org/10.1126/science.1242642">Science</a> by Olga Popova and colleagues.</p>
<p>Alongside the data from Earth is information from astronomy, planetary science, geophysics, meteoritics and cosmology. The meteorite that fell to Earth has now been classified as an LL chondrite. It formed early in the history of the Solar System, as asteroids and eventually planets condensed from the nebula.</p>
<p>Fragments of the meteorite recovered from near Chelyabinsk, including an enormous rock dredged from the bottom of Lake Chebarkul, have revealed its early history. We have all this even though less than one thousandth of the asteroid has been retrieved, and more than three quarters is estimated to have evaporated.</p>
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<span class="caption">Fragments of the meteorite recovered and the site of impact.</span>
<span class="attribution"><span class="source">Popova et al</span></span>
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<p>Measurements of the radioactive decay products from traces of uranium in the meteorite minerals show that it must have itself suffered a harsh collision during the maelstrom in which asteroids condensed, which occurred at around 115m years after the birth of the Solar System. Its existence as a discrete asteroid ended almost four and a half billion years later when it struck Russia.</p>
<p>The eyewitness reports of the airburst, as well as the damage it caused, give an idea of the sorts of effects caused by such “near miss” events. Entering the atmosphere almost 100km above the surface, at speeds of around 20km/second, the 20-metre wide asteroid set up a shockwave at 90 km altitude. By 83 km it had started to fall apart. By the time it got to around 35 km above Russia it was shining as a bright shooting star, emitting light that burnt the retinas of any watching it, and sending out a shockwave sideways from its path that blew some folk off their feet.</p>
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<p>As the video makes it clear, the shockwave broke phone networks, upset the electric grid, and interrupted the gas supply in some districts of Emanzhelinka as the valves closed in response to the vibration. No bones were broken, but some residents were hurt by flying debris and glass, while others suffered concussion.</p>
<p>Similar descriptions of the trajectory, determined from video data, are reported by in the first <a href="http://dx.doi.org/10.1038/nature12671">Nature</a> paper. Risk estimates for asteroid fireball damage have, up to now, been based on data from nuclear bomb airburst tests. In the second <a href="http://dx.doi.org/10.1038/nature12741">Nature</a> paper, researchers compare damage caused by the Chelyabinsk airburst with previous models for asteroid damage showing that the risks have been underestimated. The latest data increase the potential danger of impacts from asteroids tens of metres across.</p>
<p>These results demonstrate the forensic value of the asteroid that fell to Earth in February this year, both for assessing how such bodies come into existence, and interact with our planetary home, but also how we might assess the risk of such events into the future.</p><img src="https://counter.theconversation.com/content/19923/count.gif" alt="The Conversation" width="1" height="1" />
The asteroid impact that burst over Chelyabinsk, Russia, on the morning of February 15 has provided a huge collection of new data that scientists have been analysing since. This week, three papers, two…Simon Redfern, Professor in Earth Sciences, University of CambridgeLicensed as Creative Commons – attribution, no derivatives.