Shooting Gallery

30th June 1908: A huge explosion flattens over 800 square miles of Siberian forest in the remote region of the Podkamennaya Tunguska River. In the absence of detailed information, wild theories abound – it might have been a miniature black hole, perhaps even an alien spacecraft in difficulties. However, the general view is that it was an asteroid or comet fragment entering the Earth’s atmosphere and bursting in mid air, possibly a piece of Encke’s Comet; witness accounts mention repeated sounds like artillery, which perhaps means that Siberia was under bombardment by a series of separate fragments.

13th August 1930: There are reports of three large explosions in the Brazilian rain forest near the Peruvian border – local inhabitants talk of burning trees and a widespread ash cloud. Observatory records suggest that these were caused by one or more asteroid impacts coinciding with the peak of the annual Perseid meteor shower.

2nd February, 1932: Explorer and intelligence officer St. John Philby (father of double agent Kim Philby) discovers pieces of meteoric iron littering the remote Arabian desert in the Empty Quarter or “Rub’ al Khali”. Later, three impact craters are found in the sand at Wabar, which suggests that an asteroid exploded in mid-air over the Arabian Peninsula (with the force of a 16-kiloton nuclear weapon, approximately), maybe as recently as 1891.

16th July, 1994: The first of many fragments of comet Shoemaker-Levy 9 crash into Jupiter, the comet having been captured by the gas giant’s gravity in the 1960s or ’70s and fallen victim to Jupiter’s crushing tidal forces. Over the next few days, big pieces of comet slam into the planet’s atmosphere one after the other, creating vast dark spots which are clearly visible by telescope from Earth. The largest of these pieces (fragment G), impacting on 18th July, smashes with a force equivalent to 6,000,000 megatons.

15th February, 2013: A meteor explodes high over the Urals in Russia, creating a massive fireball, damaging buildings in six cities across the region and injuring over a thousand people (mainly cuts caused by shattering window glass). This happens 16 hours before asteroid 2012DA14 is due to pass by Earth; NASA tells us, however, that the two events are not related, the trajectories of the two objects being very different.

The meteor that lit up the skies over Chelyabinsk last week exploded with a force of nearly 500 kilotons and is estimated to have had a diameter of up to an estimated 56 feet. However, near-earth asteroid 2012DA14 which skimmed past us the same day has a diameter of around 160 feet and would have made a correspondingly bigger bang, had it collided with Earth instead – it would not have been in the Shoemaker-Levy class (thankfully!) but might have done considerably more than create smoke trails and smash windows.

To those who say that global warming is the greatest long-term threat to the human race, I think we might have to agree to disagree. In the Solar System’s great meteoric shooting gallery – going by a century’s worth of occasional impacts and near misses – it seems we have been relatively fortunate. So far, anyway.

Some useful links:

Wikipedia on the Tunguska Event:
http://en.wikipedia.org/wiki/Tunguska_event
Article on the Armagh Observatory website about the Brazilian meteors of 1930:
http://star.arm.ac.uk/impact-hazard/Brazil.html
Wikipedia on Wabar impact craters:
http://en.wikipedia.org/wiki/Wabar_craters
Wikipedia on Shoemaker-Levy 9:
http://en.wikipedia.org/wiki/Comet_Shoemaker-Levy_9
Wikipedia on the Russian meteor event of 2013:
http://en.wikipedia.org/wiki/2013_Russian_meteor_event

Signs and Portents

Much has been happening out in the world this summer – quite a lot of it weather- and/or climate-related. Floods in Pakistan, fires in Russia, and an iceberg the size of Manhattan making its maiden voyage somewhere off Greenland. Global warming or climate silly season? I’m inclined to suspect the latter, but who can be certain, really?

(That is not to say I consider extreme weather events trivial – they can be very costly, both in terms of lives and money. As with many things in life, though, I think preparedness and the wise use of resources is key.)

We shall be approaching the Autumnal Equinox all too soon, and after that, any noteworthy meteorological events here in the Northern Hemisphere are likely to be on the chilly side, and thus will be put into the “just weather” category and nothing to do with climate doom. Much like the somewhat nippy conditions they’ve had recently down in Peru and Argentina, in fact.

But anyway, I wasn’t going to write about that, and instead was planning to mention, belatedly as usual, a centenary that came up this year on 20th April – the 1910 sighting of an old friend from the outer solar system, Halley’s Comet. Nothing directly to do with climate, so this cannot really be part of my “100 Years of Climate Change” series, but some of this story can be filed under “scary stuff” or “immanent doom”, so there is a connection of sorts.

What reminded me of this missed centenary was the arrival (the weekend before last) of the Perseids, as Earth crossed the tail of Comet Swift-Tuttle, as it does every summer. (Swift-Tuttle, according to Wikipedia, has been described by somebody as “the single most dangerous object known to humanity”, by the way, being a) a big comet, b) travelling very fast, and c) having an orbit which takes it regularly just a bit too close to the Earth for comfort. I’d like to write more on this in a future article.)

Now from a modern perspective, Halley’s Comet is rather low on the ominousness (ominosity?) scale, compared to Swift-Tuttle. However, back in 1910, a threat of a very different kind was mooted. During the late 19th century, astronomers had discovered, by dint of spectroscopy, that comets contain cyanogen gas, which is poisonous. So the announcement that Earth’s atmosphere might be brushed by the tail of Halley’s Comet, on its 1910 return, set in motion a scare!

Astronomical opinion was divided, actually, Percival Lowell stating that the gas would be “so rarefied as to be thinner than any vacuum”, Camille Flammarion claiming, on the other hand that it “would impregnate the atmosphere and possibly snuff out all life on the planet.” Guess which version the mainstream media of the time plumped for!

American newspapers reported panic in many cities at the cometary tail’s approach. As the dread moment grew near (May 18th), people prepared to barricade themselves in rooms and cover the keyholes with paper. Others flocked to buy gas masks, umbrellas and “comet pills” that would help to protect them against this poison attack from space. One man, reportedly, planned to sit out the coming apocalypse at the bottom of a deep well with a suitably large bottle of whisky. Others held rooftop parties, setting out to eat, drink and be merry while they could. A newspaper article from the time described a “submarine boat” for hire, which could stay underwater for 3 days and surface once all the pestilence had dissipated (presumably its occupants could then repopulate the Earth, if representatives of both sexes had the forethought to be on board.)

One episode that strikes a chord is an AP news story which mentions Chicago schoolchildren requesting the day off school “for fear of some untoward happenings for which Halley’s Comet may be responsible” – this brought a smile to my face because of the motivation of children throughout history to avoid being at school, and also because of the wording, which is eerily reminiscent of today’s Health and Safety culture (the Safety Elves, bless them, must have been whispering their sweet nothings into people’s ears even in those days.)

Well, as we know, the world didn’t end. The perilous voyage through the poisonous tail of Halley’s Comet was a complete and utter non-event. Still, the scare didn’t go to waste – for a start, some people had become richer, having sold plenty of gas masks and comet pills. (I was going to write that HG Wells was inspired to write his novel In the Days of the Comet, which gives the poison gas idea an intriguing twist, but then realised he had written it – prophetically! – beforehand in 1906.) And the episode provides us with another chapter in the long and fascinating history of scares (of which, more anon.)

Another interesting fact about the 1910 visitation of Halley’s Comet is that many of those who, in later life, vividly remembered it blazing in the sky were actually confusing it with the earlier coming of a far brighter and more dramatic comet – the Daylight Comet of 1910, which had arrived at the beginning of the year (hence its other name – the Great January Comet.) I got my comets mixed up too, while writing this piece, quite clearly remembering the sight of Swift-Tuttle in the night sky in 1992, only to realise later that I was actually remembering Hale-Bopp in 1997.

We might laugh at the folks back in 1910 with their comet-pill silliness, but we shouldn’t, really. There are people these days who fall for scares as readily as ever, be they to do with salmonella in eggs, the threat of satanic ritual abuse or the significance of a Russian heat wave. We are the same human beings after all, just with television sets and the internet.

I enjoyed the Perseids this year, despite the light pollution over West London, which is considerable, and spent much of the evening of 13th August on the hunt for shooting stars out by Cassiopeia. There were some nice bright ones, too. It is good to know that Earth’s defensive shield is still holding up.