Text of my ‘When Worlds Collide’ column published in Ceylon Today Sunday newspaper on 23 December 2012
The much-hyped End of the World didn’t happen on December 21.
As I wrote in my blog that morning, Ass-trologers (my new name for those claiming to read our destiny in the stars) and other dabblers in pseudo-science and non-science have a lot of explaining to do.
Perhaps the greatest damage these false prophets of doom – and their uncritical multipliers in the media — did was to distract us from the real hazards that we are confronted with.
The long list includes better known threats like nuclear weapons and accelerated climate change as well as the more slowly building up ones like water scarcities, antibiotic resistance and demographic changes.
There are also some hazards that are not frequent, but have the potential to inflict planetary scale damage when they do occur. The Earth being hit by a large enough piece of space debris is one such possibility.
First, let’s clarify the terms involved. According to the US space agency NASA, little chunks of rock and debris in space are called meteoroids. They become meteors — or shooting stars — when they fall through our atmosphere, leaving a bright trail as they are heated to incandescence by air friction.
Thousands of pieces of cosmic debris enter our atmosphere every day and night — most small ones are completely burned up before hitting the ground. Pieces that survive the journey and crashland are called meteorites. Even then, average ones are too small to cause much damage. Details at: http://tiny.cc/SStar
But once in a while, a large enough piece comes along. That can be an asteroid going astray, or parts broken off a comet that periodically approaches the Sun.
Asteroids, sometimes called minor planets, are small, rocky planetary fragments left over from the formation of our Solar System. Over 10,000 of these have been discovered – ranging from the largest that is 950 km across to many that are less than a kilometre across.
Astronomers regularly monitor asteroids whose paths cross our Earth’s orbit. Called Near Earth Objects (or NEOs), some of these may pose an impact danger. But it’s important to understand the time scales and probabilities.
As NASA says, “The Earth has always been subject to impacts by comets and asteroids, although big hits are very rare. The last big impact was 65 million years ago, and that led to the extinction of the dinosaurs. Today NASA astronomers are carrying out a survey called the Spaceguard Survey to find any large near-Earth asteroids long before they hit. We have already determined that there are no threatening asteroids as large as the one that killed the dinosaurs.”
That’s certainly reassuring, as one doomsday scenario trotted out in recent weeks for ‘world ending’ involved such a planetary scale collision.
However, powerful impacts are not entirely uncommon. A sizeable chunk of asteroid or comet – even one a few dozen metres across — can create a local level disaster. The damage depends on where it lands.
There were three significant impacts during the twentieth century alone (Siberia in 1908 and 1947, and rural Brazil in 1930). In each case, damage was minimal as, miraculously, they landed on uninhabited areas. But on a crowded planet, how many times can we be so lucky?
When this hazard is discussed, some people think that it’s just as well two thirds of our planet are covered by oceans. In reality, a piece of the sky falling into the sea could trigger mega-tsunamis.
That isn’t a cosy thought as we approach the eighth anniversary of the Indian Ocean tsunami of December 2004. But the prospect has been studied seriously.
Tsunamis are usually of terrestrial origin. They are generated when the sea floor abruptly deforms and vertically displaces the overlying water. Certain types of undersea quakes trigger this reaction.
A large enough object crashing into the sea can also trigger massive waves that mimic a tsunami. A decade ago Dr Duncan Steel, a British/Australian astronomer, did some calculations about this.
He took a space rock of 200 metres in diameter colliding with Earth at a typical speed of 19 km per second. As it impacts the ocean, the object releases kinetic energy in an explosion equal to 600 megatons of TNT – or 10 times the yield of the most powerful nuclear weapon tested (underground).
Even though only about 10% of this energy would be transferred to the tsunami, such waves can carry the energy over long distances to coasts far away. They can therefore cause much more diffused destruction than would result from a land impact, he argued.
Not all scientists agree with this scenario. Some analyses during the past decade suggest that the risk of an asteroid-induced tsunami has been overstated.
In any case, such a celestial impact is far less likely to happen anytime soon. Our restless planet can produce more tectonic surprises on its own — and in our lifetimes…
But astronomers are taking no chances. In a coordinated effort that involves multiple teams scattered around the globe, they are scanning the skies day and night looking for rogue asteroids and comets.
The idea was inspired by Arthur C Clarke’s 1973 science fiction novel Rendezvous with Rama, which opened with an asteroid impact that obliterates northern Italy on the morning of 11 September 2077.
In that story, he proposed that as soon as the technology permitted, we should set up powerful radar and optical search systems to detect Earth-threatening objects. He even suggested a name: Spaceguard.
Clarke was pleased that his idea became reality in under two decades. “In terms of scientific research and policy action it inspired, Rendezvous with Rama may yet turn out to be my one piece of writing that one day saves the most number of lives,” he wrote in early 2005, in the wake of the Boxing Day tsunami.
After the mega-disaster devastated much of Sri Lanka’s coast, Clarke joined hands with astronomer Patrick Moore to raise tsunami relief funds.
At that time, the two old friends had just finished their first and only joint work, a non-fiction book coincidentally titled ‘Asteroid’. They decided to donate all proceeds to Clarke’s favoured Lankan charity, Sarvodaya.
Sir Patrick Moore, who died earlier this month aged 89, and Clarke’s brother Fred persuaded companies in the UK to help with the book’s production. The Daily Express covered printing costs, and The Independent paid for postage. Others helped with publicity, while volunteers assisted with distribution and promotion.
The book, released in May 2005 by Canopus Books in the UK, raised modest but useful donations from concerned readers.
In it, Clarke and Moore — both of who had asteroids named in their honour — discussed asteroid impact scenarios.
They summed it up with these words: “Fortunately, it is likely that we have now found all the larger ‘near Earth asteroids’. We are not immune, but the chances of civilisation being wiped out by an asteroid impact are much less than the chance that mankind will destroy itself by indulging in another senseless world war.”
That’s certainly worth pondering over, now that we have outlived false doom.
NASA NEO website: http://neo.jpl.nasa.gov
My tribute to Patrick Moore: http://tiny.cc/PMTrib