It was the largest meteorite to hit Earth in a century – and now the human and scientific fallout is clear. Today, results published simultaneously in the journals Nature and Science outline the knowledge gained from the fireball that exploded over Chelyabinsk, Russia in February, and the harm it caused. We bring you the 10 most interesting insights.
1. Meteor forensics is surprisingly low-tech
The Chelyabinsk meteor seemed to come out of nowhere, a surprise even to astronomers, but reconstructing its path needn't require high-tech equipment. Amateur videos of the meteor streaking across the sky – captured by numerous cellphones and cameras on car dashboards – were key. But to put actual distances on the footage, Peter Jenniskens of the SETI Institute in Mountain View, California, an experienced meteorite hunter, plus a team from the Russian Academy of Sciences, needed a tape measure, rope, an inclinometer and a Craftsman laser distance measuring tool. The team also drove up to 90 kilometres away to map incidents of shattered glass and interview residents who had seen, heard and smelled the explosion. "We found the markets, the grocery stores, and just talked with people behind the counter," Jenniskens says.
2. Chelyabinsk was bigger than a bomb
All this allowed the team to conclude that the object, an asteroid 17 to 20 metres across and with a mass of 10,000 tonnes, exploded at an altitude of about 30 kilometres. The initial explosion carried an energy equivalent to about 500 kilotonnes of TNT. That agrees with a separate analysis reported by Jiri Borovicka of the Academy of Sciences of the Czech Republic.
3. Most of the meteor evaporated
After the initial explosion in the sky, two larger chunks of rock survived and continued plunging through the atmosphere. One of them broke apart at an altitude of about 18 kilometres, the other sailed on to eventually land in Lake Chebarkul, leaving a 7-metre-wide hole in the ice. The latter fragment was recovered by a diver in October, and weighed in at 570 kilograms. Still, the fragments add up to only about 24 per cent of the parent body, Jenniskens thinks, so most of the material evaporated in the initial fireball.
4. Meteors cause sunburn
The most dramatic instances of damage from the airburst were flying glass and one collapsed building: most of the people who sought medical attention in the aftermath suffered from cuts and bruises. Unsurprisingly, out of 374 injured people who responded to an internet survey that Jenniskens and colleagues created, the most common complaint related to eyes – 180 people said their eyes hurt and 70 were temporarily blinded. But 20 also reported sunburn; one was burned so badly that his skin peeled. "We calculated how much UV light came down and we think it's possible," Jenniskens says. "But he was also in a snowed-in landscape, and snow is very efficient at scattering UV light. That may have helped."
5. Chemists couldn't have picked a better specimen
The meteorite's composition matches that of an LL chondrite, – the LL stands for Low iron, Low metals. These are the rarest of the "ordinary" chondrites, accounting for about 8 or 9 per cent of all meteorite falls. That means the meteorite adds to knowledge about the composition of the solar system. "If you talk about bringing an asteroid into the inner solar system, this is the type you would choose," says Jenniskens. There is one other LL chondrite whose orbit is known: the asteroid Itokawa, which the Japanese Hayabusa spacecraft visited in 2005.
6. The meteor's violent past saved Earth
One thing was odd about Chelyabinsk compared to other LL chondrites: it was shot through with cracks that had filled in with molten metal. That suggests its parent body survived an impact sometime in its history, which compressed the rock and laced it with fissures. This violent past may have helped it break up as it approached our planet, saving Earthlings from larger fragments that could have done more damage on the ground.
7. Its parents remain unknown
An earlier analysis of the meteor's orbit linked it back to asteroid 2011 EO40, a member of the Apollo family of asteroids. But Borovicka's team linked it to a different one, 86039 (1999 NC43), which is also the type of asteroid that gives rise to LL chondrites. Jenniskens and colleagues, meanwhile, used its similarity to Itokawa and its orbit to connect it to the Flora family, but claim there is too much uncertainty to link it to a specific asteroid yet.
8. We had no chance of a warning
The impact took the world by surprise – and that's not surprising. Because Chelyabinsk was so small, just 20 metres across, and because it came at Earth from the direction of the sun, we never would have seen it, even if we were looking. "This object never got bright enough to be detected by a ground-based survey," says Margaret Campbell-Brown of the University of Western Ontario in Canada. "It was basically undetectable before it hit Earth."
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