Fwd: Meteor that exploded over Russia was a 'wake-up call'

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Subject: FW: Meteor that exploded over Russia was a 'wake-up call'

6-Nov-2013
Science

First study of Russian meteor
The meteor that exploded over Chelyabinsk, Russia in February 2013 was "a wake-up call," according to a UC Davis scientist who participated in analyzing the event. The work is published Nov. 7 in the journal Science by an international team of researchers.
Russian Academy of Sciences, NASA

Contact: Andy Fell
ahfell@ucdavis.edu
530-752-4533
University of California - Davis

 

 

 

First study of Russian meteorite

November 6, 2013

A slice through a fragment of the meteorite shows numerous veins from a long-ago impact shock that weakened the original object. (Qing-zhu Yin/UC Davis photo)

The meteor that exploded over Chelyabinsk, Russia, in February 2013 was "a wake-up call," according to a University of California, Davis, scientist who participated in analyzing the event. The work is published Nov. 7 in the journal Science by an international team of researchers.

"If humanity does not want to go the way of the dinosaurs, we need to study an event like this in detail," said Qing-zhu Yin, professor in the Department of Earth and Planetary Sciences at UC Davis.

Chelyabinsk was the largest meteoroid strike since the Tunguska event of 1908, and, thanks to modern technology from consumer video cameras to advanced laboratory techniques, provides an unprecedented opportunity to study such an event, the authors note.

The Chelyabinsk meteorite belongs to the most common type of meteorite, an "ordinary chondrite." If a catastrophic meteorite strike were to occur in the future, it would most likely be an object of this type, Yin said.

The team was led by Olga Popova of the Russian Academy of Sciences in Moscow, and by NASA Ames and SETI Institute meteor astronomer Peter Jenniskens, and included 57 other researchers from nine countries.

"Our goal was to understand all circumstances that resulted in the damaging shock wave that sent over 1,200 people to hospitals in the Chelyabinsk Oblast area that day," said Jenniskens. The explosion was equivalent to about 600 thousand tons of TNT, 150 times bigger than the 2012 Sutter's Mill meteorite in California.

Based on viewing angles from videos of the fireball, the team calculated that the meteoroid entered Earth's atmosphere at just over 19 kilometers per second, slightly faster than had previously been reported.

"Our meteoroid entry modeling showed that the impact was caused by a 20-meter sized single chunk of rock that efficiently fragmented at 30 km altitude," Popova said. (A meteoroid is the original object; a meteor is the "shooting star" in the sky; and a meteorite is the object that reaches the ground.)

The meteor's brightness peaked at an altitude of 29.7 km (18.5 miles) as the object exploded. For nearby observers it briefly appeared brighter than the sun and caused some severe sunburns.

The team estimated that about three-quarters of the meteoroid evaporated at that point. Most of the rest converted to dust and only a small fraction (4,000 to 6,000 kilograms, or less than 0.05 percent) fell to the ground as meteorites. The dust cloud was so hot it glowed orange.

The largest single piece, weighing about 650 kilograms, was recovered from the bed of Lake Chebarkul in October by a team from Ural Federal University led by Professor Viktor Grokhovsky.

Shockwaves from the airburst broke windows, rattled buildings and even knocked people from their feet. Popova and Jenniskens visited over 50 villages in the area and found that the shockwave caused damage about 90 kilometers (50 miles) on either side of the trajectory. The team showed that the shape of the damaged area could be explained from the fact that the energy was deposited over a range of altitudes.

The object broke up 30 kilometers up under the enormous stress of entering the atmosphere at high speed. The breakup was likely facilitated by abundant "shock veins" that pass through the rock, caused by an impact that occurred hundreds of millions of years ago. These veins would have weakened the original meteoroid.

Yin's laboratory at UC Davis carried out chemical and isotopic analysis of the meteorites. Professor Ken Verosub, also of the Department of Earth and Planetary Sciences, measured the magnetic properties of metallic grains in the meteorite. Doug Rowland, project scientist in the Center for Molecular and Genomic Imaging at the UC Davis Department of Biomedical Engineering, contributed X-ray computed tomography scanning of the rock.

Put together, these measurements confirmed that the Chelyabinsk object was an ordinary chondrite, 4,452 million years old, and that it last went through a significant shock event about 115 million years after the formation of the solar system 4,567 million years ago. That impact was at a much later date than in other known chondrites of the same type, Yin said, suggesting a violent history.

Jenniskens calculated that the object may have come from the Flora asteroid family in the asteroid belt, but the chunk that hit the Chelyabinsk area was apparently not broken up in the asteroid belt itself. Researchers at the University of Tokyo and Waseda University in Japan found that the rock had been exposed to cosmic rays for only about 1.2 million years, unusually short for rocks originating in the Flora family.

Jenniskens speculates that Chelyabinsk belonged to a bigger "rubble pile" asteroid that broke apart 1.2 million years ago, possibly in an earlier close encounter with Earth.

The rest of that rubble could still be around as part of the near-earth asteroid population, Jenniskens said.

Yin noted that major meteorite strikes like Tunguska or Chelyabinsk occur more frequently than we tend to think. For example, four tons of material were recovered from a meteor shower in Jilin, China in 1976.

"Chelyabinsk serves as unique calibration point for high energy meteorite impact events for our future studies," he said. Technology for early detection of these objects is needed, Yin said -- such as the Large Synoptic Survey Telescope, currently being developed by an international team headed by UC Davis physics professor J. Anthony Tyson.

The work was supported by the Russian Academy of Sciences, the Office of the Governor of Chelyabinsk Oblast, NASA and the Academy of Finland.

About UC Davis

For more than 100 years, UC Davis has engaged in teaching, research and public service that matter to California and transform the world. Located close to the state capital, UC Davis has more than 33,000 students, more than 2,500 faculty and more than 21,000 staff, an annual research budget of nearly $750 million, a comprehensive health system and 13 specialized research centers. The university offers interdisciplinary graduate study and more than 100 undergraduate majors in four colleges — Agricultural and Environmental Sciences, Biological Sciences, Engineering, and Letters and Science. It also houses six professional schools — Education, Law, Management, Medicine, Veterinary Medicine and the Betty Irene Moore School of Nursing.

Media contact(s):

• Qing-zhu Yin, Earth and Planetary Sciences, (530) 220-4076, qyin@ucdavis.edu
• Andy Fell, UC Davis News Service, (530) 752-4533, ahfell@ucdavis.edu

 

 

Copyright © The Regents of the University of California, Davis campus. All Rights Reserved.

 

 

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Meteor that exploded over Russia called 'wake-up call' for Earth

DAVIS, Calif., Nov. 6 (UPI) -- The meteor that exploded over Chelyabinsk, Russia, in February should be seen as "a wake-up call," a U.S. scientist taking part in a study of the event says.

"If humanity does not want to go the way of the dinosaurs, we need to study an event like this in detail," said Qing-Zhu Yin, a professor in the Department of Earth and Planetary Sciences at the University of California, Davis.

Modern technology from consumer video cameras to advanced laboratory techniques give an unprecedented opportunity to study the event, the largest meteoroid strike since the Tunguska explosion in Siberia in 1908, researchers say.

The Chelyabinsk meteorite was the most common type of meteorite, an "ordinary chondrite," and if a catastrophic meteorite strike were to occur in the future it would most likely be an object of this type, Yin said.

Major meteorite strikes such as Tunguska or Chelyabinsk occur more frequently than people tend to think, Yin said, noting 4 tons of material were recovered from a meteor shower in Jilin, China, in 1976.

But the Russian impact is probably the best chance to make a detailed study of such events, he said.

"Chelyabinsk serves as unique calibration point for high-energy meteorite impact events for our future studies," he said, adding that technology for early detection of such objects is needed.

 

Risk of asteroid impacts may be more common than expected

Rather than expecting an impact every 150 years, researchers believe the risks could be ten times greater.

By Ananth Baliga   |   Nov. 6, 2013  |  3:34 PM  |  Updated Nov. 6, 2013 at 4:04 PM   

 

(UPI) -- Researchers warn that the risk of space rocks, like the one that exploded over Russia this February, hitting the Earth is ten times larger than previously estimated.

Using videos from security and dashboard cameras, researchers were able to reconstruct the asteroid and its trajectory through the atmosphere.

Three separate papers out this week agree that the asteroid, which caused an intense flash of blinding light at daybreak on Feb. 15 near the Russian city of Chelyabinsk, was nearly twice as heavy as earlier estimated and  had the explosive power of 500,000 tons of TNT.

"Luckily, most of the kinetic energy was absorbed by the atmosphere," said Jiri Borovicka, an asteroid researcher at the Astronomical Institute near Prague and lead author on a study published in Nature. "A more solid rock that might have blasted closer to the ground would have caused considerably more damage."

According to Borovicka, the asteroid approached the Earth from a region in the sky that is inaccessible to ground telescopes. The asteroid should have been visible six weeks before the impact, but only during the day, when the sky is too bright to spot objects of its size.

Peter Brown, a planetary scientist at the University of Western Ontario and lead author on a separate paper published in Nature, said that previous models suggested that asteroids like the Chelyabinsk asteroid would hit the earth once every 150 years. But looking at the number of observed impacts over the last 20 years suggests the impact risk could be substantially higher.

Brown suggests that a sensible response to the Chelyabinsk asteroid is scanning the visible sky with asteroid detection and early-warning system like ATLAS, which is currently being developed in Hawaii

© 2013 United Press International, Inc. All Rights Reserved. 

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Chelyabinsk asteroid smashed glass, burned skin, defied expectations

By Amina Khan

7:52 PM PST, November 6, 2013

Planetary scientists weren't remotely expecting the 62-foot-wide Chelyabinsk fireball to shoot across Russian skies in February  -- they'd had their eyes peeled on a much bigger target that missed the Earth by a decent margin, the asteroid 2012 DA14. But this relatively modest, unseen space rock caused a shock wave that shattered countless windows in the city and injured more than a thousand people.

It was the largest asteroid impact on land in more than a century. Researchers are now saying that such impacts, from relatively small asteroids just tens of yards long, might be 10 times more common than we'd thought.

The finding comes from one of three studies published in the journals Nature and Science that provide a much fuller profile of the Chelyabinsk asteroid – both its behavior and its origins. By using camera footage, seismic data and a host of other sources, scientists say they hope to better predict which asteroids are most dangerous and how they will act if they impact Earth or its atmosphere.

"If you want to calculate what happens in other circumstances in future asteroid impacts, you first need to understand Chelyabinsk," Peter Jenniskens, a research scientist at NASA's Ames Research Center in Mountain View, Calif., and one of the coauthors of the Science paper, said in an interview. "So Chelyabinsk is now the gold standard, thanks to citizen science. It is now our calibration point. And that's why it's really important to figure out what happened."

Scientists braved Russia's frigid temperatures in the asteroid's aftermath to collect what data they could.

"It was good to be there," Jenniskens said. "We visited 50 villages and talked with people in grocery stores, talked with people on the street, and everybody we talked to had a story to tell."

When it exploded about 18.5 miles above the ground, the space rock shone 30 times brighter than the sun and sent out so much ultraviolet light that eyewitnesses directly below it developed serious sunburns, Jenniskens said.

It was the largest impact since the 1908 Tunguska impact, caused by a giant asteroid that delivered a blast estimated at 10 to 50 megatons of TNT – at least 20 times more powerful than the Chelyabinsk fireball.

For the Science paper, a team led by Olga Popova of the Russian Academy of Sciences, also studied fragments recovered in the area and determined that the space rock had probably suffered an impact hundreds of millions of years ago that caused shock veins to run through it, weakening its structure. Under the tremendous stress of entering Earth's atmosphere, the weakened asteroid chunk exploded in midair.

Scientists flocked to Chelyabinsk after the space rock impact. Hundreds of cameras captured the event, making it an ideal chance for some hands-on research, scientists said.

"Clearly it was a once-in-a-lifetime opportunity," said Peter Brown, a planetary scientist at the University of Western Ontario who led one of the two studies in Nature and worked on both.

The scientists used plentiful video from 400 video cameras (typically dashboard cameras in cars) to characterize the space rock's impact on our atmosphere. They found that it exploded with the energy of 500 kilotons of TNT – roughly equivalent to a modern nuclear bomb. Fragments rained down as meteorites, including a half-ton behemoth pulled out of Lake Chebarkul.

But for that energy level, the fireball didn't do nearly as much damage as predicted for a blast that strong. The researchers think this has to do with the space rock's trajectory – it doesn't explode in essentially one place, as a bomb does – it's speeding through the air and unloading that energy as it goes. The angle of entry was also fairly shallow, Brown pointed out, further mitigating the damage.

Current models to predict an asteroid's behavior when it flies into Earth's airspace haven't taken a number of these factors into account. Models based on Chelyabinsk will help researchers find which factors they were missing. 

"We need to refine those estimates," he said.

The scientists also wanted to see how accurate our current telescope-based asteroid trackers were. They used decades of data from infrasound instruments and U.S. government sensors to pull out records of shock waves created by asteroids hitting Earth's atmosphere. Then they compared it with the telescopic data.

"We should see something like Chelyabinsk every 30 to 40 years rather than every 120 to 140 or so — a factor of three or four more of these impacts than the telescopic data suggest," Brown said.

The roughly tenfold increased risk reported by Brown's team could potentially be a slight overestimate, Paul Chodas, a research scientist in the Near Earth Object Program Office at the Jet Propulsion Laboratory in La Cañada Flintridge, said at a NASA news briefing.

But, he added, "there is an apparent discrepancy between the number of impacts in this size range being higher than previously thought … and I think this is exciting new data and more work needs to be done to settle that size discrepancy."

 

Copyright © 2013, Los Angeles Times

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More Asteroid Strikes Are Likely, Scientists Say

Eduard Kalinin

A hole blasted through the ice of Lake Chebarkul, southwest of Chelyabinsk, Russia, by a meteorite.

By KENNETH CHANG

November 6, 2013

When an asteroid exploded over the Russian city of Chelyabinsk in February, shattering windows for miles and injuring well over 1,000 people, experts said it was a rare event — of a magnitude that might occur only once every 100 to 200 years, on average.

Multimedia

YouTube Videos Unlock Meteor's Secrets

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A Meteor Streaking Through the Sky From Six Vantage Points

 

Enlarge This Image

Yekaterina Pustynnikova/Chelyabinsk.ru, via Associated Press

A contrail left by a meteor as it passed over Chelyabinsk on Feb. 15.

But now a team of scientists is suggesting that the Earth is vulnerable to many more Chelyabinsk-size space rocks than was previously thought. In research being published Wednesday by the journal Nature, they estimate that such strikes could occur as often as every decade or two.

The prospect "really makes a lot of people uncomfortable," said Peter G. Brown, a professor of physics and astronomy at the University of Western Ontario and an author of the two studies in Nature. A third paper by other scientists describing the Chelyabinsk explosion was published online this week by the journal Science.

The findings are helping to elevate the topic of planetary defense — identifying dangerous asteroids and deflecting them if necessary — from Hollywood fantasy to real-world concern.

A United Nations committee has been studying the issue for some time, and next month the General Assembly is expected to adopt two of its recommendations: establishing an International Asteroid Warning Network for countries to share information; and calling on the world's space agencies to set up an advisory group to explore technologies for deflecting an asteroid.

Sky surveys have spotted about 95 percent of the big near-Earth asteroids, those that are at least one kilometer wide, or 0.6 miles, and none are in danger of hitting Earth anytime soon.

But those are not the only ones to worry about.

"One kilometer is more than just dangerous," said Edward T. Lu, a former NASA space shuttle astronaut who heads the B612 Foundation, a private effort to launch a space telescope that could find smaller asteroids. "One kilometer is end-of-human-civilization kind of dangerous."

The Chelyabinsk asteroid was just 60 feet wide. Speeding around 40,000 miles per hour, it released energy equal to 500,000 tons of TNT. A larger asteroid, perhaps two or three times the diameter of the Chelyabinsk one, exploded over Siberia in 1908 and is estimated to have released energy equivalent to 5 million to 15 million tons of TNT, flattening millions of trees.

The proposed B612 telescope, to be called Sentinel, is intended to find asteroids about 450 feet wide, although it will also find many that are smaller. Dr. Lu said the mission would cost $450 million — $250 million to build the spacecraft and $200 million to operate it for a decade.

A 450-foot-wide asteroid, Dr. Lu said, would be equivalent to 150 million tons of TNT. "You're not going to wipe out humanity," he said, "but if you get unlucky, you could kill 50 million people or you could collapse the world economy for a century, two centuries."

Dr. Lu said astronomers had found only 10 to 20 percent of the near-Earth asteroids of that size.

Sentinel would also spot many smaller ones that could still be devastating. "What we've been talking about are the ones that would only destroy a major metropolitan area — all of New York City and the surrounding area," Dr. Lu said.

He said only about 0.5 percent of these smaller asteroids, roughly the size of the 1908 one, have been found.

Because telescope surveys have counted so few of the small asteroids, Dr. Brown and his colleagues instead investigated what has actually hit the Earth. In one of the articles in Nature, they examined United States Air Force data from the 1960s and 1970s and later data from sensors verifying a ban on aboveground nuclear weapons testing.

The recordings captured the low-frequency atmospheric rumblings generated by about 60 asteroid explosions. Most came from small asteroids, but their data suggested that the somewhat larger ones hit more frequently than would be expected based on the estimates from sky surveys. That could mean the Earth has been unlucky recently, or that the estimates on the number of Chelyabinsk-size asteroids are too low.

"Any one of them individually I think you could dismiss," Dr. Brown said, "but when you take it all together, I think the preponderance of the evidence is there is a much higher number of these tens-of-meters-size objects."

Dr. Lu said that was one more reason to launch an asteroid-finding telescope. "There are hints the rate is higher than we think, but we don't really know yet, and I think we should find out," he said. "When you find out how many there are, you also find out where the individual ones are. Everything you discover you can either rule out as going to hit us or you say, 'Hey, we ought to look at this one more carefully.' "

Many of the Chelyabinsk-size asteroids would elude detection by Sentinel. Still, the residents of Chelyabinsk would have benefited from a warning on the morning of Feb. 15 to stay away from the window. With a $5 million grant from NASA, University of Hawaii astronomers are setting up telescopes to scan the sky for quick-moving spots of light that could be oncoming asteroids. There would be no opportunity to deflect the asteroid that would hit in days or weeks, but it would give time to warn, and to evacuate. That system is scheduled to go into operation in 2015.

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A version of this article appears in print on November 7, 2013, on page A12 of the New York edition with the headline: More Asteroid Strikes Are Likely, Scientists Say.

© 2013 The New York Times Company 

 

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Russian fireball shows meteor risk may be bigger

By SETH BORENSTEIN

 

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WASHINGTON (AP) — Scientists studying the terrifying meteor that exploded without warning over a Russian city last winter say the threat of space rocks smashing into Earth is bigger than they thought.

 

Meteors about the size of the one that streaked through the sky at 42,000 mph and burst over Chelyabinsk in February — and ones even larger and more dangerous — are probably four, five or even seven times more likely to hit the planet than scientists believed before the fireball, according to three studies published Wednesday in the journals Nature and Science.

That means about 20 million space rocks the size of the Chelyabinsk one may be zipping around the solar system, instead of 3 million, NASA scientist Paul Chodas said at a news conference.

Until Chelyabinsk, NASA had looked only for space rocks about 100 feet wide and bigger, figuring there was little danger below that.

This meteor was only 62 feet across but burst with the force of 40 Hiroshima-type atom bombs, scientists say. Its shock wave shattered thousands of windows, and its flash temporarily blinded 70 people and caused dozens of skin-peeling sunburns just after dawn in icy Russia. More than 1,600 people in all were injured.

Up until then, scientists had figured a meteor causing an airburst like that was a once-in-150-years event, based on how many space rocks have been identified in orbit. But one of the studies now says it is likely to happen once every 30 years or so, based on how often these things are actually hitting.

By readjusting how often these rocks strike and how damaging even small ones can be, "those two things together can increase the risk by an order of magnitude," said Mark Boslough, a Sandia National Lab physicist, co-author of one of the studies.

View gallery."

Maps show how scientists will narrow the field of impact in the weeks approaching the time of impact …

 

Lindley Johnson, manager of NASA's Near Earth Object program, which scans the heavens for dangerous objects, said the space agency is reassessing what size rocks to look for and how often they are likely to hit.

In addition, NASA this fall reactivated a dormant orbiting telescope called WISE specifically to hunt for asteroids, Johnson said. And the agency is expanding ground-based sky searches.

At the same time, NASA and the Federal Emergency Management Agency are looking into the need for evacuations in the case of an asteroid headed for Earth and how to keep the public informed without scaring people.

Those issues came up after the two agencies quietly held a disaster drill last spring in Washington that was meant to simulate what would happen if a space rock slightly bigger than the Chelyabinsk one threatened the East Coast.

During the drill, when it looked as if the meteor would hit just outside the nation's capital, experts predicted 78,000 people could die. But when the mock meteor ended up in the ocean, the fake damage featured a 49-foot tsunami and shortages of supplies along the East Coast, according to an after-action report obtained by The Associated Press.

The exercise and the studies show there's a risk from smaller space rocks that strike before they are detected — not just from the giant, long-seen-in-advance ones like in the movie "Armageddon," said Bill Ailor, a space debris expert at the Aerospace Corporation who helped coordinate the drill.

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This photo provided by The Field Museum in Chicago, taken April 9, 2013, shows pieces of a meteor th …

 

"The biggest hazard from asteroids right now is the city-busting airbursts, not the civilization-busting impacts from 1-kilometer-diameter objects that has so far been the target of most astronomical surveys," Purdue University astronomer Jay Melosh, who wasn't part of the studies, wrote in an email.

"Old-fashioned civil defense, not Bruce Willis and his atom bombs, might be the best insurance against hazards of this kind."

Chodas said the Chelyabinsk rock surprised astronomers because it was coming from the direction of the sun and was not detectable. Telescopes can see some space rocks as small as 3 feet wide, but some are simply too dark to spot, he said.

Scientists said a 1908 giant blast over Siberia, a 1963 airborne explosion off the coast of South Africa, and others were of the type that is supposed to happen less than once a century, or in the case of Siberia, once every 8,000 years, yet they all occurred in a 105-year timespan.

Because more than two-thirds of Earth is covered with water and other vast expanses are uninhabited deserts and ice, other past fireballs could have gone unnoticed.

Just this week, NASA got a wake-up call on those bigger space rocks that astronomers thought they had a handle on, discovering two 12-mile-wide asteroids and a 1.2-mile-wide one that had escaped their notice until this month. However, NASA said the three objects won't hit Earth.

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FILE - In this Feb. 15, 2013 file photo provided by Chelyabinsk.ru, shows a meteorite contrail over  …

 

Asteroids are space rocks that circle the sun as leftovers of failed attempts to form planets billions of years ago. When asteroids enter Earth's atmosphere, they become meteors. (When they hit the ground, they are called meteorites.)

The studies said the Chelyabinsk meteor probably split off from a much bigger space rock.

What happened in the Russian city of 1 million people is altering how astronomers look at a space rocks. With first-of-its-kind video, photos, satellite imagery and the broken-up rock, scientists have been able to piece together the best picture yet of what happens when an asteroid careens into Earth's atmosphere. It's not pretty.

"I certainly never expected to see something of this scale or this magnitude," said University of Western Ontario physicist Peter Brown, lead author of one study. "It's certainly scary."

Scientists said the unusually shallow entry of the space rock spread out its powerful explosion, limiting its worst damage but making a wider area feel the effects. When it burst it released 500 kilotons of energy, scientists calculated.

"We were lucky. This could have easily gone the other way. It was really dangerous," said NASA meteor astronomer Peter Jenniskens, co-author of one of the papers. "This was clearly extraordinary. Just stunning."

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Online:

NASA's Near Earth Object Program: http://neo.jpl.nasa.gov

Nature: http://www.nature.com/nature

The journal Science: http://www.sciencemag.org

Copyright © 2013 The Associated Press. All rights reserved. 

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Russian Fireball Fallout: Huge Asteroid Numbers Raise Stakes of Impact Threat

By Mike Wall, Senior Writer   |   November 07, 2013 07:00am ET

Impact site of the main mass of the Chelyabinsk meteorite in the ice of Lake Chebarkul. Image released Nov. 6, 2013. Credit: Eduard Kalinin View full size image

The number of asteroids zooming close to Earth is far greater than previously believed, highlighting the need to ramp up efforts to find and track these potentially dangerous space rocks, experts say.

A new analysis of the Russian meteor explosion that injured more than 1,000 people in the city of Chelyabinsk this past February estimates that similar impacts occur about seven times more often than previously thought.

This 3D simulation of the Chelyabinsk meteor explosion of Feb. 15, 2013 by Mark Boslough was rendered by Brad Carvey using the CTH code on Sandia National Laboratories' Red Sky supercomputer. Andrea Carvey composited wireframe tail.
Credit: Andrea Carvey, Mark Boslough & Brad Carvey

View full size image

That means there could be more than 20 million near-Earth asteroids roughly 62 feet (19 meters) wide — the size of the Chelyabinsk object — rather than three or four million, scientists say, adding to the Russian meteor explosion's importance as a teachable moment. [See Photos of the Russian Meteor Explosion of Feb. 15]

"It has attracted more attention to the threat," Lindley Johnson, program executive for NASA's Near-Earth Object (NEO) Observations Program, said of the Chelyabinsk event in a teleconference with reporters Wednesday (Nov. 6).

The Russian meteor explosion is a "great advertisement," he added, "that this is really something that we do need to be dealing with, and addressing the improvement in capabilities to detect, track and characterize these objects."

The Feb. 15, 2013 meteor blast over Chelaybinsk damaged hundreds of buildings and injured more than a thousand people. [See the full Russian meteor infographic here.
Credit: Karl Tate, SPACE.com contributor

Out of the blue

 

The Russian meteor caught scientists and citizens of Chelyabinsk by surprise, exploding without warning on Feb. 15. The shock wave created by the blast — which was equivalent to about 500 kilotons of TNT — shattered windows throughout the area, sending more than 1,200 people to the hospital. (There were no fatalities.)

It's not terribly surprising that the Chelyabinsk airburst came out of the blue. Scientists have discovered just 10,000 or so near-Earth objects to date, out of a total population that numbers in the millions.

And that population is likely significantly larger than scientists had realized, suggests the new study, which was published Wednesday (Nov. 6) in the journal Nature.

Main mass of the Chelyabinsk fall at the Chelyabinsk State Museum of Local History shortly after recovery from Chebarkul Lake. Photo courtesy of Andrey Yarantsev. Image released Nov. 6, 2013.
Credit: Science/AAAS

The researchers, led by Peter Brown of the University of Western Ontario in Canada, performed a global survey of recent airbursts packing at least 1 kiloton of energy. They concluded that the number of Chelyabinsk-like events — and, by extension, Chelyabinsk-meteor-size asteroids — appears to be about seven times greater than previously estimated.

While this calculation must be taken with a grain of salt because it's based on a small sample size, it does imply that the number of near-Earth asteroids in the 50- to 100-foot-range (15 to 30 meters) has likely been underestimated in the past, other researchers say.

"I'm uncomfortable to go out on a quote saying that it's actually seven times more at that size range," said Paul Chodas, a research scientist with the NEO Program Office at NASA's Jet Propulsion Laboratory in Pasadena, Calif., who was not involved in the study. "But I would say it appears to be several times more."

Hunting for asteroids

Astronomers have spotted 95 percent of the 980 near-Earth asteroids at least 0.6 miles (1 km) wide, which might end civilization if they hit us. But if they want to start making real progress in detecting smaller objects like the Chelyabinsk impactor, new tools will likely be needed.

At the top of many scientists' wish list is an infrared space telescope that would hunt for asteroids from inside the orbit of Earth, so it could stare out at our planet's neighborhood without having to fight the glare of the sun.

Such an instrument is already on the drawing board. The nonprofit B612 Foundation, which is dedicated to helping protect Earth against catastrophic asteroid impacts, aims to launch its Sentinel Space Telescope to a Venus-like orbit in 2018. Sentinel should find about 500,000 near-Earth asteroids in less than six years of operation, B612 officials have said.

But defending the planet effectively against space rocks involves more than the launch of one telescope, researchers say. Rather, detecting dangerous asteroids — and eventually deflecting them away from Earth — will require a concerted and sustained international effort, which has likely gotten a boost from the drama in the skies over Chelyabinsk on Feb. 15.

"It's provided, certainly, incentive by not only the U.S. government but nations around the world and the United Nations to improve our coordination of capabilities against this natural threat to the Earth," Johnson said.

 

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