Cometry Airburst or Earth Burp?

Last Friday, a meteorite hurtling towards the Russian Ural mountains made the headlines when it exploded into a fireball flying across our skies (video at end of post). The shockwave produced by it’s escapade into out atmosphere smashed windows and caused injuries to hundreds of people. Friday’s meteorite encounter made me think back to a lesser known, and more mysterious, encounter with a object in our skies. Was it, or was it not a meteorite….?

7:14 am 30 June 1908, Tunguska River, Siberia
The sky turned to fire, a deafening bang was heard, a strong super-heated wind swept by. Mr. Semenoc, and old man sitting on his porch, was thrown backwards by an immense shock wave. Windows smashed.

30 June 2008, Krasnoyarsk, Russia
100 years to the day, scientists meet to debate, argue and ultimately answer the question ‘What really caused the Tunguska event?’

A mystery story
Over the remote and swampy forests of central Siberia something from above, or below ground blasted with the energy of 185 Hiroshima bombs. Sturdy trees instantaneously fell, radiating outwards for 2000 square kilometers. 65 km away from the central blast, Mr Semenov was picking himself off the floor. Something so huge should be easy to understand right? The Tunguska event is still baffling scientists today.

Tunguska comet event
Damage after the 1908 Tunguska event in Siberia (nytimes.com)

Scientific mysteries like this get under the skin of scientists. It’s remarkable that with the rapid scientific progress over the century, we’re only creeping towards answering the conundrum. It was lucky the Tunguska event happened where it did, in this remote forested region the damage was limited and there was no loss of life. It’s hard to image was devastation may have ensued had it been over London. But what if this event was to happen again, this time actually over a densely populated city? We need to know what caused it, how it happened and could it happen again?

31st June 1908 – London
It’s nighttime but not as you’ve ever seen it. The night sky was so bright that you could sit outside happily reading a newspaper. If you look up, in the uppermost atmosphere, you’ll be able to see thin, almost luminescent clouds; they’re much higher in the sky than normal clouds usually are. These rarities are noctilucent clouds and they form only in specific conditions – quite a coincidence that they appear just a day after the impact.

A mystery comet
By far, the most popular explanation is that an icy comet, or a stoney meteorite, blew up in the sky above Siberia; it fits in with what witnesses saw. This scenario sees an icy/stoney body around 10-30 meters across come hurtling towards Earth. However, the journey through our protective atmosphere is a dangerous one and it heats up, cracks and starts to fall apart. Eventually, 5 km above the ground it gives up and violently explodes – an airburst. By numerical modeling we can place constraints on the size, speed and composition of this body.

But – the inevitable ‘but’ – what’s not there is the problem. Debris of the comet, or meteorite, and an impact crater from the shockwave should hiding amongst the forests. The area has been searched with a toothcomb – no one has found anything. However, in 2007 Lake Cheko has been proposed to be the remnants of a crater. Although crater experts currently dispute this hypothesis.

Lake Cheko, Siberia (http://www-th.bo.infn.it/tunguska/09-cheko-30june08.htm)
Lake Cheko, Siberia (http://www-th.bo.infn.it/tunguska/09-cheko-30june08.htm)

A mystery earth burp
Without a crater or comet leftovers, scientists are forced to think outside the box. Astrophysicist Kundt believes that it’s not up in the sky we should be looking for evidence but from deep within the Earth. He believes that and earthquake triggered up to 10 million tones of natural gas exploded at subsonic speeds from the ground – an earth burp.

Here we have a geophysical vs. the extra-terrestrial theory. From 2009 the extra-terrestrial is in the lead, championed by the evidence of European noctilucent clouds. The presence of the clouds indicate that there must be vast amount of water high up in the atmosphere and computer simulations have calculated that this water can travel vast distances by the means of huge swirling atmospheric eddies, explaining the bright night skies in London.

Whilst the cometry answer is becoming ever more plausible there is still the issue of the absence of crater and no one has ever come across cometry shards in the surrounding area.

It’s important to have opposing theories battling right up to the point where the answer is almost beyond doubt. If an idea comes through that’s probable and no one contests it, then given time it gets ingrained almost as science fact. It’s unclear here is how an earth burp could cause such atmospheric disturbances, such as the noctilucent clouds across London for instance.

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