6 Nov 2013 - NASA and International Researchers Obtain Crucial Data from Meteoroid Impact

[NASA]

http://solarsystem.nasa.gov/planets/images/default-asteroids.jpg (http://solarsystem.nasa.gov/news/display.cfm?News_ID=45412)6 Nov 2013 - NASA and International Researchers Obtain Crucial Data from Meteoroid Impact
A team of NASA and international scientists for the first time have gathered a detailed understanding of the effects on Earth from a small asteroid impact.


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[Cristian]

http://solarsystem.nasa.gov/news/display.cfm?News_ID=45412

NASA and International Researchers Obtain Crucial Data from Meteoroid Impact
6 Nov 2013
(Source: NASA/Ames Research Center/SETI Institute)

A team of NASA and international scientists for the first time have gathered a detailed understanding of the effects on Earth from a small asteroid impact.

The unprecedented data obtained as the result of the airburst of a meteoroid over the Russian city of Chelyabinsk on Feb. 15, 2013, has revolutionized scientists' understanding of this natural phenomenon.

The Chelyabinsk incident was well observed by citizen cameras and other assets. This provided a unique opportunity for researchers to calibrate the event, with implications for the study of near-Earth objects (NEOs) and developing hazard mitigation strategies for planetary defense. Scientists from nine countries have now established a new benchmark for future asteroid impact modeling.

"Our goal was to understand all circumstances that resulted in the shock wave," said meteor expert Peter Jenniskens, co-lead author of a report published in the journal Science. Jenniskens, a meteor astronomer at NASA's Ames Research Center and the SETI Institute, participated in a field study led by Olga Popova of the Institute for Dynamics of Geospheres of the Russian Academy of Sciences in Moscow in the weeks following the event.

"It was important that we followed up with the many citizens who had firsthand accounts of the event and recorded incredible video while the experience was still fresh in their minds," said Polpova.

By calibrating the video images using the position of the stars in the night sky, Jenniskens and Popova calculated the impact speed of the meteor at 42,500 mph (19 kilometers per second). As the meteor penetrated through the atmosphere, it efficiently fragmented into pieces, peaking at 19 miles (30 kilometers) above the surface. At that point the light of the meteor appeared brighter than the sun, even for people 62 miles (100 kilometers) away.

Due to the extreme heat, many of the pieces of the debris vaporized before falling out of the orange glowing debris cloud. Scientists believe that between 9,000 to 13,000 pound (4,000 to 6,000 kilograms) of meteorites fell to the ground. This included one fragment approximately 1,400 pound (650 kilogram) recovered from Lake Chebarkul on October 16, 2013, by professional divers guided by Ural Federal University researchers.

NASA researchers participating in the 59 member consortium study suspect that the abundance of shock fractures in the rock contributed its break up in the upper atmosphere. Meteorites made available by Chelyabinsk State University researchers were analyzed to learn about the origin of the shock veins and their physical properties.

"One of these meteorites broke along one of these shock veins when we pressed on it during our analysis," said Derek Sears, a meteoriticist at Ames.

Mike Zolensky, a cosmochemist at NASA's Johnson Space Center in Houston, may have found why these shock veins (or shock fractures), were so frail. They contained layers of small iron grains just inside the vein, which had precipitated out of the glassy material when it cooled.

"There are cases where impact melt increases a meteorite's mechanical strength, but Chelyabinsk was weakened by it," said Zolensky.

The impact that created the shock veins may have occurred as long ago as 4.4 billion years. This would have been 115 million years after the formation of the solar system, according to the research team, who found that the meteorites had experienced a significant impact event at that time.

"Events that long ago affected how the Chelyabinsk meteoroid broke up in the atmosphere, influencing the damaging shockwave," said Jenniskens.

Research is being conducted to better understand the origin and nature of NEOs. These essential studies are needed to inform our approach to preparing for the potential discovery and deflection of an object on a collision course with the Earth.
NASA's recently announced asteroid initiative will be the first mission to capture and relocate an asteroid. It represents an unprecedented technological feat that will lead to new scientific discoveries and technological capabilities that will help protect our home planet.

Aside from representing a potential threat, the study of asteroids and comets represent a valuable opportunity to learn more about the origins of our solar system, the source of water on the Earth, and even the origin of organic molecules that lead to the development of life.

For more information about the Chelyabinsk field study visit: http://cams.seti.org/index-chelyabinsk.html

For more information on asteroids and comets, visit: http://www.nasa.gov/mission_pages/asteroids/main/

For more information about NASA, visit: http://www.nasa.gov

[Cristian]

http://www.newscientist.com/article/dn24542-csi-chelyabinsk-10-insights-from-russias-meteorite.html?full=true#.UnyMxHAqwb4

CSI Chelyabinsk: 10 insights from Russia's meteorite

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06 November 2013 by Lisa Grossman


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."

9. Its friends are still out there

From Chelyabinsk and other recorded airbusts, Campbell-Brown and her colleagues estimate that the number of objects with diameters of 10 metres or more that could hit Earth is 10 times as large as previously assumed. Many of them, like Chelyabinsk, are invisible. "Without massive space-based surveys, these will get by us fairly often," she says.

10. It could have been worse

The meteor came in at an oblique angle, which spread its energy over a large area. Scientists often compare the damage an incoming asteroid might do to that of a nuclear weapons test of equivalent energy, but Chelyabinsk proves that this model doesn't work in all cases. "For any one point on the ground, the damage was less than you might expect for a nuclear weapon," she says. On the other hand, most of the damage Chelyabinsk caused came from its shock wave. If it had come straight down at Earth, the shock wave would have been distributed horizontally in the atmosphere, vastly reducing its reach. "It's kind of a trade-off," Campbell-Brown says.