Surprise! Fireballs Light up the Radio Sky, Hinting at Unexplored Physics

At any given moment, it seems, the sky is sizzling with celestial phenomena waiting to be stumbled upon. New research using the Long Wavelength Array (LWA), a collection of radio dishes in New Mexico, found quite the surprise. Fireballs — those brilliant meteors that leave behind glowing streaks in the night sky — unexpectedly emit a low radio frequency, hinting at new unexplored physics within these meteor streaks.

The LWA keeps its eyes to the sky day and night, probing a poorly explored region of the electromagnetic spectrum. It’s one of only a handful of blind searches carried out below 100 MHz.

Over the course of 11,000 hours, graduate student Kenneth Obenberger from the University of New Mexico and colleagues found 49 radio bursts, 10 of which came from fireballs.

Most of the bursts appear as large point sources, limited to four degrees, roughly eight times the size of the full Moon. Some, however, extend several degrees across the sky. On January 21, 2014, a source left a trail covering 92 degrees in less than 10 seconds (see above). The end point continued to glow for another 90 seconds.

The only known astrophysical object with this ability is a fireball. So Obenberger and colleagues set out to see if NASA’s All Sky Fireball Network had detected anything at the same location and time as the bursts.

While the network shares only a portion of the sky with the LWA, the fireballs seen in this direction matched fireballs caught by NASA. Additionally, most bursts did occur directly after the peak of a bright meteor shower.

The top panel is a histogram showing the number of events per day as compared to several major meteor showers (red lines).
The top panel is a histogram showing the number of events per day as compared to several major meteor showers (red lines).

The fireballs detected here are extremely energetic, traveling with an average velocity of 68 km/s, near the upper end of the meteorite velocity spectrum (from 11 km/s to 72 km/s).

They can be seen in the radio due to radio forward scattering. When fast-moving meteoroids strike Earth’s atmosphere they heat and ionize the air in their path. The luminous ionized trails reflect radio waves. During a meteor shower these waves can not only be picked up by vast arrays, such as the one in New Mexico, but by your TV and AM/FM radio transmitter.

Whereas most fireballs have been detected well over 100 MHz, “we’ve discovered that they also produce a low frequency pulse,” says Obenberger’s PhD advisor, Gregory Taylor.

This pulse is telling us something about the physical conditions in the plasma created by the meteor.  “It could be cyclotron radiation (emitted from moving charges in a magnetic field), or perhaps some sort of plasma wave leakage from the trail, or maybe something completely different,” says Obenberger. “It’s too early to tell at the moment.”

Meteors come in a range of energies and sizes. So investigating this unexpected signature further will yield new insights into the interaction between meteors and our atmosphere.

“This is just the beginning,” says Taylor. “Now we have to put this new technique to use — find out more about the spectrum of the pulse and the meteors that produce it. It’s an entirely new way of looking at meteors and how they interact with our atmosphere.”

If you’re curious what’s currently emitting radio waves in the New Mexico sky check out the LWA’s live radio cam.

The paper was published in Astrophysical Journal Letters today and is available for download here.

Camelopardalid Meteor Shower Skimpy but Sweet

So how were the ‘Cams’ by you? Based on a few reports via e-mail and my own vigil of two and a half hours centered on the predicted maximum of  2 a.m. CDT (7 UT) Saturday morning the Camelopardalid meteor shower did not bring down the house. BUT it did produce some unusually slow meteors and (from my site) one exceptional fireball with a train that lasted more than 20 minutes. 

The 'Cam' left a long train across the Milky Way in the Summer Triangle. Credit: Bob King
This ‘Cam’ left a long train across the Milky Way inside the Summer Triangle. Credit: Bob King

I saw 10 meteors in all, most of them slow and colorful with orange and yellow predominating. My hopes were high when the shower started with a bang. At 12:34 CDT, a brilliant, very slow moving meteor flashed below Polaris at about magnitude -1.  A prominent train glowed many seconds after burnout and continued to show for more than 20 minutes in the camera and telescope. At low magnification in my 15-inch reflector (37-cm) the persistent glow looked like a brand new sausage-shaped diffuse nebula in Cassiopeia.

2.5 minute time exposure showing the persistent train left by a near-fireball brightness Camelopardalid meteor. The five bright stars form the familiar 'W' of Cassiopeia. Credit: Bob King
2.5 minute time exposure showing the persistent train left by a brilliant Camelopardalid meteor. The five bright stars to the right outline the familiar ‘W’ of Cassiopeia. Credit: Bob King

Trains form when a meteoroid’s hypersonic velocity through the upper atmosphere ionizes the air along the object’s path. When the atoms return to their rest states, they release that pent up energy  as a glowing streak of light that gradually fades. The train in the photos expands and changes shape depending on the vagaries of upper atmospheric winds. Absolutely fascinating to watch.

Pretty scene with the Big Dipper (upper left), a lake and a 'Cam' taken from Sudbury, Canada. Credit: Bill Longo
Lovely scene with the Big Dipper (upper left) and a ‘Cam’ taken from Sudbury, Canada. Credit: Bill Longo

Most activity occurred between 12:30 and 2 a.m. for my time zone in the U.S. Midwest. Surprisingly, the action dropped off around 2 and stayed that way until 3. I did get one ‘farewell Cam’ on that last look up before turning in for the night.

Malcolm Park of Toronto captured a bright Camelopardalid this morning.
Malcolm Park of Toronto captured a bright Camelopardalid this morning.

The team working with Gianluca Masi at the Virtual Telescope Project reported a number of bright meteors as well but no storm. We share several of their photos here. As more information comes in, please drop by for a more complete report. You can also check out Dirk Ross’s Latest Worldwide Meteor News for additional first hand reports.

The strange streak with a moving satellite (?) at its center than drifted from Leo to Auriga early this morning. The starlike object makes a narrower streak inside the cloud during the time exposure. Credit: Bob King
The strange streak with a moving satellite (?) at its center that drifted from Leo to Auriga early this morning. The starlike object made a narrower streak inside the cloud during the time exposure. Credit: Bob King

Before signing off for the moment, I’d like to ask your help in explaining a strange phenomenon I saw while out watching and photographing the shower. Around 1 a.m. I looked up and noticed a comet-like streak about 15-degrees long drifting across northern Leo. My first thought was meteor train – a giant one – but then I noticed that the center of the streak was brighter and contained a starlike object that moved in tandem with the wispy glow. I quickly took a couple pictures as the streak traveled north and expanded into a large, nebulous ray that persisted for about 1o minutes. There were no other clouds in the sky and the aurora was not active at the time.

Photo taken a couple minutes after the first one showing the expanding ray. The starlike object is the brighter trail within the ray near bottom. Credit: Bob King
Photo taken a couple minutes after the first one showing the expanding ray. The starlike object is the brighter trail within the ray near bottom. Credit: Bob King

Can anyone shed light on what it was??

UPDATE: According Mike McCants, satellite tracking software developer, the plume is fuel dump connected to the launch of a new Japanese mapping satellite. One never knows sometimes what the night has in store.

 

Dashcams, Tweets Show Bright Daytime Fireball Over Ontario, Canada on May 4

A rare daylight meteor streaked across the skies over southern Ontario, Canada and the U.S. Northeast during the afternoon of Sunday May 4, 2014, with brightness “rivaling that of the Sun,” said the American Meteor Society. Reports of a bright fireball followed by a loud sonic boom were reported on social media, and several dashcam videos emerged showing the fireball, showing an unusual vertical trajectory.

Experts estimated the space rock that caused the excitement as being about half to one meter in diameter and exploding with a force of 50 tons of TNT energy. Canadian meteor expert Peter Brown, a professor at the University of Western Ontario said in the Winnipeg Free Press that he is confident that the fireball was large enough that some meteorite fragments may have hit the ground. .

Compared to the meteor that exploded over Chelyabinsk, Russia in February of 2013, that’s quite small. That meteor’s explosion shattered windows and injured 1,000 people.

See more videos, tweets and images below, and you can read a liveblog of the event (with lots of links) by Daniel Fischer (@cosmos4u).

Read more news reports at the American Meteor Society, Globe and Mail, and Global News.

Weekly Space Hangout – April 25, 2014: Asteroids, ISS Repairs & an Annular Eclipse

Host: Fraser Cain
Guests: Morgan Rehnberg, Brian Koberlein, David Dickinson, Jason Major

This Week’s Stories:
Morgan Rehnberg (cosmicchatter.org / @cosmic_chatter):
EVA
Cosmos
SpaceX announcements

Brian Koberlein (@briankoberlein, briankoberlein.com):
Meteors are not more likely to hit Earth

Dave Dickinson (@astroguyz, www.astroguyz.com):
Saturn at Opposition
Bizarre Annular Eclipse

Jason Major (@JPMajor, LightsInTheDark.com):
B612 Foundation asteroid announcement

We record the Weekly Space Hangout every Friday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch us live on Google+, Universe Today, or the Universe Today YouTube page.

Norwegian Skydiver Almost Gets Hit by Falling Meteor — and Captures it on Film

It sounds like a remarkable story, almost unbelievable: Anders Helstrup went skydiving nearly two years ago in Hedmark, Norway and while he didn’t realize it at the time, when he reviewed the footage taken by two cameras fixed to his helmet during the dive, he saw a rock plummet past him. He took it to experts and they realized he had captured a meteorite falling during its “dark flight” — when it has been slowed by atmospheric braking, and has cooled and is no longer luminous.

UPDATE: See our new article on this topic: Follow Up on Skydiving Meteorite: Crowdsourcing Concludes it Was Just a Rock

Respected Norwegian astrophysicist Pål Brekke confirmed to Universe Today that the story is true and the video is authentic. “I was part of the investigation – and kept secret for two years – in hope of finding the meteorite,” Brekke said via a conversation on Twitter.

Since the search for the meteorite has come up empty so far, Helstrup’s story and video has been released in an effort to recruit more people to look for the rock — and to confirm that this actually was a meteorite.

“It has been a little hard to keep it as a secret,” Helstrup told Universe Today via email, “but everyone has been loyal to the project and helped us out!”

Here’s the video:

The rock zooms by at about :15 in this video:

You can watch a slower version in the video below.

Helstrup has been searching with friends, family and volunteers after getting advice from experts from the Geological Museum in Oslo, Norwegian Space Centre and Norwegian meteor network, making painstaking efforts to pinpoint the location of where the meteorite fell.

“The meteorite has for sure some possible hiding spots,” Helstrup said. “There is a forest with lots of different places it can easily disappear. Even if there is several areas where it would be found easily, there is a river, some marshy spots and areas and lots of high grass. Therefore the best chance of a finding would be in springtime. But we have high hopes!”

Finding the rock would provide the definitive confirmation it really was a space rock that Helstrup captured on film. There’s been much debate about the veracity of both the video and the claim (read Phil Plait’s look at the evidence) but in fact, it is Helstrup who might be most skeptical this was a meteor. There are experts, however, who say there is no doubt.

“It can’t be anything else,” said geologist Hans Amundsen, quoted in the Norwegian publication NRK. “The shape is typical of meteorites – a fresh fracture surface on one side, while the other side is rounded.”

He added that the meteorite may have been part of a larger rock that had exploded perhaps 20 kilometers above Helstrup.

What if the rock would have hit Helstrup or his diving partner? Amundson said the rock would have cut him in half.

“Imagine a 5 kilo rock hitting you in the chest at 300 kilometers per hour,” Amundson says in the video. “That would have led to quite an accident investigation.”

This is unique because — if confirmed — this is the first time a meteor in dark flight has been captured on film.

“Fireballs entering the atmosphere have been filmed many times,” says Morten Bilet in the video. Bilet is a meteorite expert. “This is unique because it was filmed during its so called “dark flight” – after it has been burned out. That’s never been done before so this is something new and exciting.”

We’ve asked Helstrup to keep us posted on any developments in this story or if the meteorite is found.

You can read more about the story from NRK, and the Norwegian Space Center, and the Norwegian Meteorite Society.

Experts Question Claim Tunguska Meteorite May Have Come from Mars

In 1908 a blazing white line cut across the sky before exploding a few miles above the ground with a force one thousand times stronger than the nuclear blast that leveled Hiroshima, Japan.

The resulting shock wave felled trees across more than 800 square miles in the remote forests of Tunguska, Siberia.

For over 100 years, the exact origins of the Tunguska event have remained a mystery. Without any fragments or impact craters to study, astronomers have been left in the dark. That’s not to say that all kinds of extraordinary causes haven’t been invoked to explain the event. Various people have thought of everything from Earth colliding with a small black hole to the crash of a UFO.

Russian researchers claim they may finally have evidence that will dislodge all conspiracy theories, but that “may” is huge. A team of four believes they have recovered fragments of the object — the so-called Tunguska meteorite — and even think they are Martian in origin. The research, however, is being called into question.

In a detective-like manner, the team surveyed 100 years’ worth of research. The researchers read eyewitness reports and analyzed aerial photos of the location. They performed a systematic survey of the central region in the felled forest and analyzed exotic rocks and penetration funnels.

A schematic of the Tunguska event. Image Credit:
A schematic of the central region in the felled forest due to the Tunguska event. Image Credit: Anfinogenov et al.

Previously, numerous expeditions failed to recover any fragments that could be attributed conclusively to the long-sought Tunguska meteorite. But then Andrei Zlobin, of the Russian Academy of Sciences’ Vernadsky State Geological Museum, discovered three stones with possible traces of melting. He published the results in April 2013.

Zlobin’s discovery paper was received with skepticism and Universe Today covered the news immediately. A curious question arose quickly: why did it take so long for Zlobin to analyze his samples? The expedition took place in 1988, but it took 20 years before the three Tunguska candidates were nominated and another five years before Zlobin finished the paper.

By Zlobin’s admission, his discovery paper was only a preliminary study. He claimed he didn’t carry out a detailed chemical analysis of the rocks, which is necessary in order to reveal their true nature. Most field experts quickly dismissed the paper, feeling there was more work to be done before Zlobin could truly know if these rocks were fragments from the Tunguska meteor.

Today, new research is moving forward with an analysis of the rocks originally discovered by Zlobin. But an interesting new addition to the collection is a rock called “John’s Stone” — a large boulder discovered in July, 1972. While it’s mostly a dark gray now it was much lighter at the time of its discovery. “John’s Stone has an almond-like shape with one broken side,” lead author Dr. Yana Anfinogenov told Universe Today.

Now the skeptical reader might be asking the same question as before: why is there such a large time-lapse between the discovery of John’s Stone and the analysis presented here? (It’s interesting to note that while this elusive rock has been reviewed in the literature for over 40 years, this is the first time it has appeared in an English paper). Anfinogenov claimed that new data (especially concerning Martian geology) allowed for a much better analysis today than it did in recent years.

Photos (1972) of John's Stone and related findings. Image Credit:
Photos (1972) of John’s Stone and related findings. Image Credit: Anfinovenov et al.

“The ground near John’s Stone presents undeniable impact signs suggesting that the boulder hit the ground with a catastrophic speed,” Anfinogenov told Universe Today. It left a deep trace in the permafrost which allowed researchers to note its trajectory and landing velocity coincides with that of the incoming Tunguska meteorite.

John’s Stone also contains shear-fractured splinter fragments with glossy coatings, indicating the strong effect of heat generated when it entered our atmosphere. The research team attempted to reproduce those glossy coatings found on the splinters by heating another fragment of John’s Stone to 500 degrees Celsius. The experiment was not successful as the fragment disintegrated in high heat.

“The authors do not present a strong case that the boulder known as John’s Stone was involved in the Tunguska event, or that it originated from Mars,” said Dr. Phil Bland, a meteorite expert at Curtin University in Perth, Australia.

They claim the mineral structure and chemical composition of the rocks — a quartz-sandstone with grain sizes of 0.5 to 1.5 cm and rich in silica — match rocks found on Mars. But their paper lacks any microanalysis of the samples, or isotopic study.

While there is a strong case that an impact on Mars could easily eject rock fragments that would then hit the Earth, something doesn’t match up. “The physics of ejecting material from Mars into interplanetary space argues for fragments with diameters of one to two meters, not the 20 to 30 meter range that would be required for Tunguska,” Bland told Universe Today.

It seems as though planetary geologists will require a much stronger case than this to be truly convinced John’s Stone is the Tunguska meteorite, let alone from Mars.

The paper is currently under peer-review but is available for download here.

Satellite Watches Dust from Chelyabinsk Meteor Spread Around the Northern Hemisphere

When a meteor weighing 10,000 metric tons exploded 22.5 km (14 miles) above Chelyabinsk, Russia on Feb. 15, 2013, the news of the event spread quickly around the world. But that’s not all that circulated around the world. The explosion also deposited hundreds of tons of dust in Earth’s stratosphere, and NASA’s Suomi NPP satellite was in the right place to be able to track the meteor plume for several months. What it saw was that the plume from the explosion spread out and wound its way entirely around the northern hemisphere within four days.

The bolide, measuring 59 feet (18 meters) across, slipped quietly into Earth’s atmosphere at 41,600 mph (18.6 kilometers per second). When the meteor hit the atmosphere, the air in front of it compressed quickly, heating up equally as quick so that it began to heat up the surface of the meteor. This created the tail of burning rock that was seen in the many videos that emerged of the event. Eventually, the space rock exploded, releasing more than 30 times the energy from the atom bomb that destroyed Hiroshima. For comparison, the ground-impacting meteor that triggered mass extinctions, including the dinosaurs, measured about 10 km (6 miles) across and released about 1 billion times the energy of the atom bomb.

Atmospheric physicist Nick Gorkavyi from Goddard Space Flight Center, who works with the Suomi satellite, had more than just a scientific interest in the event. His hometown is Chelyabinsk.

“We wanted to know if our satellite could detect the meteor dust,” said Gorkavyi, who led the study, which has been accepted for publication in the journal Geophysical Research Letters. “Indeed, we saw the formation of a new dust belt in Earth’s stratosphere, and achieved the first space-based observation of the long-term evolution of a bolide plume.”

The team said they have now made unprecedented measurements of how the dust from the meteor explosion formed a thin but cohesive and persistent stratospheric dust belt.

About 3.5 hours after the initial explosion, the Ozone Mapping Profiling Suite instrument’s Limb Profiler on the NASA-NOAA Suomi National Polar-orbiting Partnership satellite detected the plume high in the atmosphere at an altitude of about 40 km (25 miles), quickly moving east at about 300 km/h (190 mph).

The day after the explosion, the satellite detected the plume continuing its eastward flow in the jet and reaching the Aleutian Islands. Larger, heavier particles began to lose altitude and speed, while their smaller, lighter counterparts stayed aloft and retained speed – consistent with wind speed variations at the different altitudes.

By Feb. 19, four days after the explosion, the faster, higher portion of the plume had snaked its way entirely around the Northern Hemisphere and back to Chelyabinsk. But the plume’s evolution continued: At least three months later, a detectable belt of bolide dust persisted around the planet.

Gorkavyi and colleagues combined a series of satellite measurements with atmospheric models to simulate how the plume from the bolide explosion evolved as the stratospheric jet stream carried it around the Northern Hemisphere.

“Thirty years ago, we could only state that the plume was embedded in the stratospheric jet stream,” said Paul Newman, chief scientist for Goddard’s Atmospheric Science Lab. “Today, our models allow us to precisely trace the bolide and understand its evolution as it moves around the globe.”

NASA says the full implications of the study remain to be seen. Scientists have estimated that every day, about 30 metric tons of small material from space encounters Earth and is suspended high in the atmosphere. Now with the satellite technology that’s capable of more precisely measuring small atmospheric particles, scientists should be able to provide better estimates of how much cosmic dust enters Earth’s atmosphere and how this debris might influence stratospheric and mesospheric clouds.

It will also provide information on how common bolide events like the Chelyabinsk explosion might be, since many might occur over oceans or unpopulated areas.

“Now in the space age, with all of this technology, we can achieve a very different level of understanding of injection and evolution of meteor dust in atmosphere,” Gorkavyi said. “Of course, the Chelyabinsk bolide is much smaller than the ‘dinosaurs killer,’ and this is good: We have the unique opportunity to safely study a potentially very dangerous type of event.”

Source: NASA

An Early Start for Noctilucent Clouds

The season for noctilucent “night-shining” clouds is arriving in the northern hemisphere, when wispy, glowing tendrils of high-altitude ice crystals may be seen around the upper latitudes, shining long after the Sun has set. Found about 83 km (51 miles) up, noctilucent clouds (also called polar mesospheric clouds) are the highest cloud formations in the atmosphere. They’ve been associated with rocket launches and space shuttle re-entries and are now thought to also be associated with meteor activity… and for some reason, this year they showed up a week early.


Noctilucent clouds (NLCs) form between 76 to 85 kilometers (47 to 53 miles) above Earth’s surface when there is just enough water vapor to freeze into ice crystals. The icy clouds are illuminated by the Sun when it is just below the horizon, after darkness has fallen, giving them their night-shining properties. This year NASA’s AIM spacecraft, which is orbiting Earth on a mission to study high-altitude ice, started seeing noctilucent clouds on May 13th.

AIM map of noctilucent clouds over the north pole on June 8 (Credit: LASP/University of Colorado)
AIM map of noctilucent clouds over the north pole on June 8
(Credit: LASP/University of Colorado)

“The 2013 season is remarkable because it started in the northern hemisphere a week earlier than any other season that AIM has observed,” reports Cora Randall of the Laboratory for Atmospheric and Space Physics at the University of Colorado. “This is quite possibly earlier than ever before.”

The early start is extra-puzzling because of the solar cycle. Researchers have long known that NLCs tend to peak during solar minimum and bottom-out during solar maximum — a fairly strong anti-correlation. “If anything, we would have expected a later start this year because the solar cycle is near its maximum,” Randall says. “So much for expectations.”

Read more on the NASA AIM page here, and watch the [email protected] video below for the full story. (Also, check out some very nice NLC photos taken last week in the UK by Stuart Atkinson at Cumbrian Sky.)

Source: NASA

With Russian Meteor Fresh In Everyone’s Memory, ESA Opens An Asteroid Monitoring Center

It’s been about three months since that infamous meteor broke up over Chelyabinsk, Russia. In that time, there’s been a lot of conversation about how we can better protect ourselves against these space rocks with a potentially fatal (from humanity’s perspective) gravitational attraction to Earth.

This week, the European Space Agency officially inaugurated a “NEO Coordination Centre” that is intended to be asteroid warning central in the European Union. It will be the hub for early warnings on near-Earth objects (hence the ‘NEO’ in the name) under ESA’s space situational awareness program.

ESA estimates that of the 600,000 asteroids and comets that orbit the Sun, about 10,000 of them are NEOs. (They define NEOs as asteroids or comets with sizes of several feet up to several tens of miles.)

NASA, of course, is also gravely concerned about the threat NEOs present. Its administrator, Charles Bolden, talked about this at a Congressional hearing about asteroids in March.

Before delving into the threat, Bolden took a metaphorical deep breath to talk about the dozens of asteroids — a meter or larger — that slam into Earth’s atmosphere each year. Most of them burn up harmlessly, and further, 80 tons of dust-like material rain on Earth daily.

A notable meteor that did cause some damage took place about 100 years ago, in 1908, when an object broke up over an isolated area in Russia and flattened trees for miles. Bolden characterized that as a statistically one-in-a-thousand year event, but added that the “real catch” is this type of event could happen at any time.

NASA, however, is seeking out those that cause a threat. It is supposed to find 90 per cent of asteroids 140 meters or larger by 2020, and is making progress towards that goal. (By comparison, the Chelyabinsk object was estimated at 17 to 20 meters.)

Nine radar images of near-Earth asteroid 2007 PA8 obtained between by NASA's 230-foot-wide (70-meter) Deep Space Network antenna. The part of the asteroid closest to the antenna is at top. Credit: NASA/JPL-Caltech
Nine radar images of near-Earth asteroid 2007 PA8 obtained between by NASA’s 230-foot-wide (70-meter) Deep Space Network antenna. The part of the asteroid closest to the antenna is at top. Credit: NASA/JPL-Caltech

So how to best monitor the threat? Bolden outlined a few ideas: crowdsourcing, coordinating with other federal agencies and making use of automatic feeds from different telescopes throughout the world (as NASA does right now.)

Bolden emphasized that none of the asteroids we have found is on a collision course with the Earth. Still, NASA and other science experts are not complacent.

In the same hearing, John Holdren — the president’s assistant on science and technology — recommended following a National Academy of Sciences report to spend upwards of $100 million a year on asteroid detection and characterization. To mitigate the threat, Holdren further recommended a visit to an asteroid by 2025, which would perhaps cost $2 billion.

Possible Meteorite Fragments from 1908 Tunguska Explosion Found

The 1908 explosion over the Tunguska region in Siberia has always been an enigma. While the leading theories of what caused the mid-air explosion are that an asteroid or comet shattered in an airburst event, no reliable trace of such a body has ever been found. But a newly published paper reveals three different potential meteorite fragments found in the sandbars in a body of water in the area, the Khushmo River. While the fragments have all the earmarks of being meteorites from the event – which could potentially solve the 100-year old mystery — the only oddity is that the researcher actually found the fragments 25 years ago, and only recently has published his findings.

Like the recent Chelyabinsk airburst event, the Tunguska event likely also produced a shower of fragments from the exploding parent body, scientists have thought. But no convincing evidence has ever been found from the June 30, 1908 explosion that occurred over the Tunguska region. The explosion flattened trees in a 2,000 square kilometer area. Luckily, that region was largely uninhabited, but reportedly one person was killed and there were very few people that reported the explosion. Forensic-like research has determined the blast was 1,000 times more powerful than a nuclear bomb explosion, and it registered 5 on the Richter scale.

Previous expeditions to the region turned up empty as far as finding meteorites; however one expedition in 1939 by Russian mineralogist Leonid Kulik found a sample of melted glassy rock containing bubbles, which was considered evidence of an impact event. But the sample was somehow lost and has never undergone modern analysis.

The expedition in 1998 by Andrei Zlobin from the Russian Academy of Sciences was initially unsuccessful in finding meteorites or evidence of impacts. He made several drill holes in the peat bogs in the area and while he found evidence of the explosion, he didn’t find any meteorites. He then decided to look in the nearby river shoal.

Zlobin gathered about 100 samples of rocks that had features of potential meteorites, but further examination produced just three rocks with tell-tale features like melting and regmalypts – the , thumblike impressions found on the surface of meteorites which are caused by ablation as the hot rock falls through the atmosphere at high speed.

Zlobin writes that “After the expedition the author focused his efforts on experimental investigation of thermal processes and mathematical modeling of the Tunguska impact [Zlobin, 2007],” and he used tree ring evidence to estimate the temperatures from the event, and concluded that rocks already on the ground would not have been changed or melted from the blast, and therefore any rocks having evidence of melting should be from the impactor itself.

Zlobin says he has not yet carried out a detailed chemical analysis of the rocks, which would reveal their chemical and isotopic composition. But he does say the stony fragments do not rule out a comet since the nucleus could easily contain rock fragments. However, he has calculated the density of the impactor must have been about 0.6 grams per cubic centimeter, which is about the same as nucleus of Halley’s comet. Zlobin says that initially, the evidence seems “excellent confirmation of cometary origin of the Tunguska impact.”

While there is nothing definitive yet from Zlobin’s new paper – and there is the question of why he waited so long to conduct his study – his work provides hope for a better explanation of the Tunguska event as opposed to some rather off-the-wall ideas that have been proposed, such as a Tesla death-ray or an explosion of methane gas from the bogs.

The Technology Review blog writes that “clearly there is more work to be done here, particularly the chemical analysis perhaps with international cooperation and corroboration.”

Read Zlobin’s paper, Discovery of probably Tunguska meteorites at the bottom of Khushmo river’s shoal

Source: MIT Technology Review