Reference text: Galina Zaglumyonova was woken in her flat in central Chelyabinsk by an enormous explosion that blew in the balcony windows and shattered clay pots containing her few houseplants. When she jumped out of bed on Friday she could see a huge vapour trail hanging in the morning sky and hear the wail of car alarms from the street below. I did not understand what was going on, said Zaglumyonova. There was a big explosion and then a series of little explosions. My first thought was that it was a plane crash. What she had actually witnessed were the death throes of a 10tonne meteorite that plunged to Earth in a series of fireballs just after sunrise. Officials put the number of people injured at almost 1,200, with more than 40 taken to hospital most as a result of flying glass shattered by the sonic boom created by the meteorites descent. There were no reported deaths. The meteorite entered the atmosphere travelling at a speed of at least 33,000mph and broke up into chunks between 18 and 32 miles above the ground, according to a statement from the Russian Academy of Sciences. The event caused panic in Chelyabinsk, a city of more than 1 million people to the south of Russia's Ural mountains, as mobile phone networks swiftly became jammed by the volume of calls. Amateur video footage from the area, often peppered with the obscene language of frightened observers, showed the chunks of meteorite glowing more brightly as they approached the moment of impact. The vapour trail was visible for hundreds of miles around, including in neighbouring Kazakhstan. Tatyana Bets was at work in the reception area of a hospital clinic in the centre of the city when the meteorite struck. First we noticed the wind, and then the room was filled with a very bright light and we could see a cloud of some unspecified smoke in the sky, she said. Then, after a few minutes, came the explosions.

Complementary text 1: The meteorite is providing invaluable information to help protect against larger rocks that might pose a serious threat to Earth The meteorite fireball that fell over Chelyabinsk briefly burned 30 times brighter than the sun. Photograph AP Just after sunrise on 15 February 2013, as commuters made their way along snowcovered roads to Chelyabinsk in southwest Russia, the clear blue sky was torn by a hurtling lump of space rock. The meteorite appeared without warning, out of the sun, on a shallow trajectory. It thumped into the atmosphere at 12 miles per second and became a fireball. For a moment, the rock burned 30 times brighter than the sun. Viktor Grokhovsky, a researcher at Ural Federal University, 200km to the north of Chelyabinsk, missed the beautiful, terrifying spectacle that morning, but within minutes was watching video of the event. He spent the rest of the day assembling a search party. The first of several set out at first light the next morning to interview eyewitnesses and recover pieces of the fallen rock. It was rather easy to find fragments in the first days after the meteorite fell, because the chunks left holes in the snow, Grokhovsky told the Guardian. But as more snow fell over the next two weeks, the holes became covered over. The search was called off until the snow began to melt in the spring. Nothing the size of the Chelyabinsk meteorite had fallen to Earth in 100 years, and never over an urban centre where its dramatic arrival would be captured by CCTV and dashboard video cameras installed by Russians wary of insurance scams and crooked police. This was the first time in modern, medieval or ancient history when a meteorite fell in an area with a high density population. This type of meteorite is rare and a lot of material fell. All these factors give excellent opportunities for extraterrestrial substance research. The hazard from asteroids and comets, peoples behaviour in emergencies, and the shortage of astronomical education are all on the agenda, said Grokhovsky. After the flash came the bang. The meteorite exploded with a force around 30 times that of the atom bomb dropped on Hiroshima, or 500 kilotonnes of TNT. The shockwave knocked people off their feet and shattered windows in thousands of apartments.

Complementary text 2: Photograph Niyazz /Alamy In February, a meteor exploded over the Russian city of Chelyabinsk, causing significant damage. A recent study in Nature suggests that there are more of these potentially threatening small meteors than we previously thought. We ask expert Dr Hugh Lewis from the University of Southampton to explain how we can tackle meteors, big and small. We've been looking now for a number of years to try to identify all the objects that are larger than 1km in size objects that size are going to cause a lot of damage should they hit the Earth. When you get down to smaller size, we can only see some of those objects, basically because they are darker we rely on them reflecting light from the sun to see them in telescopes and so the smaller they get, the less sunlight they are going to be reflecting. As you saw with the event over Chelyabinsk, an object that was probably less then 20m in size can have quite a significant impact on the ground. The meteor itself broke up before it hit the ground but the airburst caused all the damage the broken windows, throwing people across rooms, and structural damage. We have the Spaceguard Survey and there are people now who are advocating the use of space based missions to look for asteroids. The B612 Foundation is proposing a mission called Sentinel, where a spacecraft will be launched into a Venus like orbit to look for objects larger than 140m. If an asteroid is coming to us from the direction of the Sun, we cant observe it easily with a telescope.

Summary (65% relevance & 90% fusion for concepts): Galina Zaglumyonova was woken in her flat in central Chelyabinsk by an enormous explosion that blew in the balcony windows and shattered clay pots containing her few houseplants. When she jumped out of bed on Friday she could see a huge vapour trail hanging in the morning sky and hear the wail of car alarms from the street below. I did not understand what was going on, said Zaglumyonova. There was a big explosion and then a series of little explosions. Viktor Grokhovsky, a researcher at Ural Federal University, 200km to the north of Chelyabinsk, missed the beautiful, terrifying spectacle that morning, but within minutes was watching video of the event. It was rather easy to find fragments in the first days after the meteorite fell, because the chunks left holes in the snow, Grokhovsky told the Guardian. What she had actually witnessed were the death throes of a 10tonne meteorite that plunged to Earth in a series of fireballs just after sunrise. Officials put the number of people injured at almost 1,200, with more than 40 taken to hospital most as a result of flying glass shattered by the sonic boom created by the meteorites descent. There were no reported deaths. The meteorite entered the atmosphere travelling at a speed of at least 33,000mph and broke up into chunks between 18 and 32 miles above the ground, according to a statement from the Russian Academy of Sciences. The meteorite exploded with a force around 30 times that of the atom bomb dropped on Hiroshima, or 500 kilotonnes of TNT. The event caused panic in Chelyabinsk, a city of more than 1 million people to the south of Russia's Ural mountains, as mobile phone networks swiftly became jammed by the volume of calls. Amateur video footage from the area,often peppered with the obscene language of frightened observers, showed the chunks of meteorite glowing more brightly as they approached the moment of impact. Nothing the size of the Chelyabinsk meteorite had fallen to Earth in 100 years, and never over an urban centre where its dramatic arrival would be captured by CCTV and dashboard video cameras installed by Russians wary of insurance scams and crooked police. The vapour trail was visible for hundreds of miles around, including in neighbouring Kazakhstan. Tatyana Bets was at work in the reception area of a hospital clinic in the centre of the city when the meteorite struck. This type of meteorite is rare and a lot of material fell. Then, after a few minutes, came the explosions.

Complementary text 1: Galina Zaglumyonova was woken in her flat in central Chelyabinsk by an enormous explosion that blew in the balcony windows and shattered clay pots containing her few houseplants. When she jumped out of bed on Friday she could see a huge vapour trail hanging in the morning sky and hear the wail of car alarms from the street below. I did not understand what was going on, said Zaglumyonova. There was a big explosion and then a series of little explosions. My first thought was that it was a plane crash. What she had actually witnessed were the death throes of a 10tonne meteorite that plunged to Earth in a series of fireballs just after sunrise. Officials put the number of people injured at almost 1,200, with more than 40 taken to hospital most as a result of flying glass shattered by the sonic boom created by the meteorites descent. There were no reported deaths. The meteorite entered the atmosphere travelling at a speed of at least 33,000mph and broke up into chunks between 18 and 32 miles above the ground, according to a statement from the Russian Academy of Sciences. The event caused panic in Chelyabinsk, a city of more than 1 million people to the south of Russia's Ural mountains, as mobile phone networks swiftly became jammed by the volume of calls. Amateur video footage from the area, often peppered with the obscene language of frightened observers, showed the chunks of meteorite glowing more brightly as they approached the moment of impact. The vapour trail was visible for hundreds of miles around, including in neighbouring Kazakhstan. Tatyana Bets was at work in the reception area of a hospital clinic in the centre of the city when the meteorite struck. First we noticed the wind, and then the room was filled with a very bright light and we could see a cloud of some unspecified smoke in the sky, she said. Then, after a few minutes, came the explosions.

Complementary text 2: The meteorite is providing invaluable information to help protect against larger rocks that might pose a serious threat to Earth The meteorite fireball that fell over Chelyabinsk briefly burned 30 times brighter than the sun. Photograph AP Just after sunrise on 15 February 2013, as commuters made their way along snowcovered roads to Chelyabinsk in southwest Russia, the clear blue sky was torn by a hurtling lump of space rock. The meteorite appeared without warning, out of the sun, on a shallow trajectory. It thumped into the atmosphere at 12 miles per second and became a fireball. For a moment, the rock burned 30 times brighter than the sun. Viktor Grokhovsky, a researcher at Ural Federal University, 200km to the north of Chelyabinsk, missed the beautiful, terrifying spectacle that morning, but within minutes was watching video of the event. He spent the rest of the day assembling a search party. The first of several set out at first light the next morning to interview eyewitnesses and recover pieces of the fallen rock. It was rather easy to find fragments in the first days after the meteorite fell, because the chunks left holes in the snow, Grokhovsky told the Guardian. But as more snow fell over the next two weeks, the holes became covered over. The search was called off until the snow began to melt in the spring. Nothing the size of the Chelyabinsk meteorite had fallen to Earth in 100 years, and never over an urban centre where its dramatic arrival would be captured by CCTV and dashboard video cameras installed by Russians wary of insurance scams and crooked police. This was the first time in modern, medieval or ancient history when a meteorite fell in an area with a high density population. This type of meteorite is rare and a lot of material fell. All these factors give excellent opportunities for extraterrestrial substance research. The hazard from asteroids and comets, peoples behaviour in emergencies, and the shortage of astronomical education are all on the agenda, said Grokhovsky. After the flash came the bang. The meteorite exploded with a force around 30 times that of the atom bomb dropped on Hiroshima, or 500 kilotonnes of TNT. The shockwave knocked people off their feet and shattered windows in thousands of apartments.

Reference text: Photograph Niyazz /Alamy In February, a meteor exploded over the Russian city of Chelyabinsk, causing significant damage. A recent study in Nature suggests that there are more of these potentially threatening small meteors than we previously thought. We ask expert Dr Hugh Lewis from the University of Southampton to explain how we can tackle meteors, big and small. We've been looking now for a number of years to try to identify all the objects that are larger than 1km in size objects that size are going to cause a lot of damage should they hit the Earth. When you get down to smaller size, we can only see some of those objects, basically because they are darker we rely on them reflecting light from the sun to see them in telescopes and so the smaller they get, the less sunlight they are going to be reflecting. As you saw with the event over Chelyabinsk, an object that was probably less then 20m in size can have quite a significant impact on the ground. The meteor itself broke up before it hit the ground but the airburst caused all the damage the broken windows, throwing people across rooms, and structural damage. We have the Spaceguard Survey and there are people now who are advocating the use of space based missions to look for asteroids. The B612 Foundation is proposing a mission called Sentinel, where a spacecraft will be launched into a Venus like orbit to look for objects larger than 140m. If an asteroid is coming to us from the direction of the Sun, we cant observe it easily with a telescope.

Summary (75% relevance & 90% fusion for concepts): It was rather easy to find fragments in the first days after the meteorite fell, because the chunks left holes in the snow, Grokhovsky told the Guardian. A recent study in Nature suggests that there are more of these potentially threatening small meteors than we previously thought. We ask expert Dr Hugh Lewis from the University of Southampton to explain how we can tackle meteors, big and small. We've been looking now for a number of years to try to identify all the objects that are larger than 1km in size objects that size are going to cause a lot of damage should they hit the Earth. When you get down to smaller size, we can only see some of those objects, basically because they are darker we rely on them reflecting light from the sun to see them in telescopes and so the smaller they get, the less sunlight they are going to be reflecting. As you saw with the event over Chelyabinsk, an object that was probably less then 20m in size can have quite a significant impact on the ground. Amateur video footage from the area, often peppered with the obscene language of frightened observers, showed the chunks of meteorite glowing more brightly as they approached the moment of impact. This was the first time in modern, medieval or ancient history when a meteorite fell in an area with a high density population. The meteor itself broke up before it hit the ground but the airburst caused all the damage the broken windows, throwing people across rooms, and structural damage. We have the Spaceguard Survey and there are people now who are advocating the use of space based missions to look for asteroids. The B612 Foundation is proposing a mission called Sentinel, where a spacecraft will be launched into a Venus like orbit to look for objects larger than 140m. If an asteroid is coming to us from the direction of the Sun, we cant observe it easily with a telescope.