Asteroid Impacts on Earth Obstructed by Red Tape

Artist's view of last year’s fireball explosion over Chelyabinsk, Russia – termed a "superbolide" event.

Credit: Don Davis

Red tape is making it tougher for researchers to study and characterize asteroid strikes on Earth, which are apparently more common than previously thought, experts say.

The bureaucratic snafu affects the use of U.S. government space assets that help scientists study "airbursts" like the meteor that exploded without warning over Russia last year.

At issue is the ability to combine space data with outputs from a global network of seismic, infrasound and hydroacoustic sensors that have been deployed worldwide to provide treaty verification for a nuclear test ban.

This network is the International Monitoring System (IMS) overseen by the Comprehensive Nuclear Test Ban Treaty Organization (CTBTO).

In recent years, the IMS has detected shock waves from many airbursts, providing further evidence that asteroid impacts are more frequent than previously thought.

Ideally, matching observations from spacecraft with measurements from CTBTOs infrasound detectors would give scientists more of a heads-up on what's raining down on Earth, experts say.



Memorandum of agreement
Last year, the Air Force Space Command signed a memorandum of agreement with NASA's Science Mission Directorate.

That document, inked on Jan. 18, 2013, spelled out specifics for the public release of meteor data from sources such as high-flying, secretive U.S. government space sensors.

With that agreement in place, NASA's Near Earth Object (NEO) Observation Program started receiving information on fireball events based on analysis of data collected by U.S. government sensors.

Details of atmospheric meteor explosions, as recorded by U.S. military spacecraft sensors, were posted on a publicly accessible NASA website run by the Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

In fact, the military-civil cooperation was spurred by the details of the February 2013 fireball explosion over Chelyabinsk, Russia, termed a "superbolide" event.

The website postings are designed to assist the scientific community's investigation of bolides, or exceptionally bright fireballs.

However, multiple scientists noted that the JPL website had not been updated recently. That presumably meant that there was some sort of delay, as some fairly big events were detected by infrasound in the last year.

"Because of budget and personnel reductions on our military partner, they ran into workforce issues to accomplish this task," said Lindley Johnson, NEO program executive within the Planetary Science Division of NASA's Science Mission Directorate in Washington, D.C.

"We are already in discussions with them about what it will take to get it restarted," Johnson told reporters

Russian Chelyabinsk meteor shockwave circled the Earth twice

The shock wave from an asteroid that burned up over Russia in February was so powerful that it travelled twice around the globe, scientists say.

They used a system of sensors set up to detect evidence of nuclear tests and said it was the most powerful event ever recorded by the network.

More than 1,000 people were injured when a 17m, 10,000-tonne space rock burned up above Chelyabinsk.

The study appears in the journal Geophysical Research Letters.

The researchers studied data from the International Monitoring System (IMS) network operated by the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO).

The detection stations look out for ultra-low frequency acoustic waves, known as infrasound, that could come from nuclear test explosions but the system can also detect large blasts from other sources, such as the Chelyabinsk fireball.

Alexis Le Pichon, from the Atomic Energy Commission in France and colleagues report that the explosive energy of the impact was equivalent to 460 kilotonnes of TNT.

This makes it the most energetic event reported since the 1908 Tunguska meteor in Siberia.

Russian Meteor Impact: What is known? Technical Details

The large fireball (technically, a "superbolide") observed on the morning of February 15, 2013 in the skies near Chelyabinsk, Russia, was caused by a relatively small asteroid approximately 17 to 20 meters in size, entering the Earth's atmosphere at high speed and a shallow angle.

In doing so it released a tremendous amount of energy, fragmented at high altitude, and produced a shower of pieces of various sizes that fell to the ground as meteorites.

The fireball was observed not only by video cameras and low frequency infra-sound detectors, but also by U.S. Government sensors.

As a result, the details of the impact have become clearer. There is no connection between the Russian fireball event and the close approach of asteroid 2012 DA14, which occurred just over 16 hours later.

New Fireball Data
U.S. Government sensor data on fireballs are now reported on the NASA Near-Earth Object Program Office website.

The February 15th event is the first entry on this new site, and it provides the following information about the fireball:

• Date and time of maximum brightness: 15 Feb. 2013/03:20:33 GMT
• Geographic location of maximum brightness: Latitude: 54.8 deg. N :: Longitude: 61.1 deg. E
• Altitude of maximum brightness: 23.3 km (14.5 miles)
• Velocity at peak brightness: 18.6 km/s (11.6 miles/s)
• Approximate total radiated energy of fireball: 3.75 x 10^14 Joules. This is the equivalent of about 90 kilotons (kt) of TNT explosives, but it does not represent the total impact energy (see note below).
• Approximate total impact energy of the fireball in kilotons of TNT explosives (the energy parameter usually quoted for a fireball): 440 kt.

Note that the total energy of a fireball event is several times larger than the observed total radiated energy.

The JPL fireballs website uses the following empirical formula derived by Peter Brown and colleagues to convert the optical radiant energy Eo into an estimate of the total impact energy E (see: Brown et al., The flux of small near-Earth objects colliding with the Earth. Nature, vol. 420, 21 Nov. 2002, pp. 294-296):.

E = 8.2508 x E_o ^0.885

During the atmospheric entry phase, an impacting object is both slowed and heated by atmospheric friction.

In front of it, a bow shock develops where atmospheric gases are compressed and heated. Some of this energy is radiated to the object causing it to ablate, and in most cases, to break apart.

Fragmentation increases the amount of atmosphere intercepted and so enhances ablation and atmospheric braking.

The object catastrophically disrupts when the force from the unequal pressures on the front and back sides exceeds its tensile strength.

This was an extraordinarily large fireball, the most energetic impact event recognized since the 1908 Tunguska blast in Russian Siberia.

The meteorites recovered from the Chelyabinsk fireball are reported to be ordinary chondrites, which have a typical density of about 3.6 g/cm^3.

Given the total energy of about 440 kt, the approximate effective diameter of the asteroid would be about 18 meters, and its mass would be roughly 11,000 tons.

NB: All estimates of total energy, diameter and mass are very approximate.

Russian Asteroid Impact: Chelyabinsk gripped by 'meteor fever'

Russia's Chelyabinsk region is gripped by a kind of meteor fever, with thousands combing through fields trying to find meteorite fragments.

Near the villages of Deputatsky and Pervomaysky, an hour's drive from Chebarkul city, whole families of meteorite hunters are hard at work. 

The meteorite passed over the area before reportedly crashing into the Chebarkul lake, and the snowy fields are covered with human footprints.

The nearby home of the Belizkaya family was filled with soot from their oven after the meteorite explosion, which caused the ceiling to crack. Initially frightened, now the family calls that day their "rebirth", and have so far found three 1cm-wide meteorite fragments.

"We came with all the family, we do it out of interest, really, this is such a memento of that event," says Elena Belizkaya of the hoard. "We'll keep it at home for now, but if there's a chance to sell it, we'll sell some, of course!"

Meteorite hunters require no particular expertise as the hunt is relatively simple - a meteorite's impact leaves a small crater similar to a mouse's hole.

If you find such a hole in a bank of snow you can be certain - it's either a mouse or a meteorite. The BBC team found four tiny stones within five minutes.

Most of those fragments found near Deputatsky are pea-sized, but some can be much bigger - more like golf balls. The biggest fragment we saw weighed about 100g.

It was found by a citizen of Chelyabinsk, who said he had received several offers from friends in Moscow. "It's like hunting or fishing," said one meteorite hunter.

"When you see an animal, your heart starts to beat fast, and when you're fishing - it's like pulling the fishing rod and thinking there's something extraordinary. This is the same - you see a tiny hole, try it, and here it is."

Space stones
Space stones Scientists from the meteorite laboratory at the Russian Academy of Science collecting samples in Chelyabinsk say the more meteorite hunters the merrier, because there are only a couple of days of good weather left for the search.



The mineral which the meteorite is made of - chondrite - is common and not of great interest. But size matters.

Any wind or snowfall will destroy meteorite traces, and small fragments will simply not be found until the spring, when the fields will be covered by tall grass.

The mineral which the meteorite is made of - chondrite - is common and not of great interest, says junior research associate Dmitry Sadilenko. But its size matters.

The Chebarkul meteorite is one of the largest on record - preliminary estimates suggest it was the size of a skyscraper. And the bigger the fragment found, the more it is worth.

What's more, according to Russia's Subsoil Law, there are no legal grounds for prohibiting people from collecting, selling and exporting meteorite fragments.

However, potentially lucrative finds are already raising eyebrows. The Internet is full of ads selling so-called fragments of the Chebarkul meteorite, with prices ranging from a few thousand to 500,000 roubles (£11,000).

Lucrative hole in the ice
The Chelyabinsk police department has already questioned one "businessman" - a resident of Emanzhelinka village - who has sold several fragments for 15,000 roubles.

He could be charged with fraud if the stones are found to be fake. Lucrative hole in the ice Although scientists from the Ural Federal University have declared Chebarkul Lake to be the location of the main meteorite fall - suggesting a fragment as wide as 50cm may be lying on the lake bed - the Chelyabinsk authorities say they cannot confirm this.

Chelyabinsk deputy governor Igor Murog told the BBC that the large ice-hole thought to have been made by the meteorite could equally have been made by a fisherman.



Locals charge the price of an expensive Moscow taxi ride to take meteorite hunters to the Chebarkul lake ice hole. 

Meteor hunters, though, seem not to care about official statements: Many are drilling holes in the ice and lowering magnets attached to ropes into the water. For now they are finding mostly tiny fragments.

Even Chebarkul Mayor Andrey Orlov joined in the hunt, sending divers into the lake's cold water soon after the meteorite fall, only for their mission to be thwarted by silt on the lake-bed. The hunt will continue on Monday.

 He has announced a competition for business ideas as Chebarkul tries to profit from its status as the only city where meteorite fragments are known to have landed.

And locals are already cashing in, offering to shuttle visitors to the site of the now-famous ice-hole via horse and cart - for the price of an expensive Moscow taxi fare.