The End of the World as We Know It

     

Apocalyptic thought has a tradition that dates to the Persian prophet Zoroaster in the 14th century BC. Recently, anxiety has grown over the prediction of the end of the world in the Mayan calendar.

Impact!: The Threat of... Gerrit Verschuur Best Price: $0.99 Buy New $4.57 (as of 10:10 UTC - Details)

It’s true that the Mayan odometer will hit zeros on 21 December 2012, as it reaches the end of a 394-year cycle called a baktun. But this baktun is part of a larger 8,000-year cycle called a pictun, and there’s no evidence that anything astronomically untoward will happen as the current baktun slides into the next. However, that hasn’t stopped the feverish speculating that sells books and cinema tickets.

What kind of catastrophe would it take to end the world? Astronomical intruders provide a potentially serious threat. Impacts can be caused by stray rubble from the Asteroid Belt and the rocky snowballs that travel in highly elliptical orbits in the comet cloud. There are many fewer large bits of debris than small bits, so the interval between large impacts is much longer than the interval between small impacts.

That’s good news. Every century or so, a 10-meter meteor slams into the Earth with the force of a small nuclear device. Tunguska was the site of the last, in 1908, and it was pure luck that that meteor landed in the uninhabited wilderness of Siberia. Every few thousand years, Earth can pass through unusually thick parts of the debris trail of comets, turning the familiar light show of a meteor shower into a deadly firestorm. Roughly every 100,000 years, a projectile hundreds of meters across unleashes power equal to the world’s nuclear arsenals. The result is devastation over an area the size of England, global tidal waves (if the impact is in the ocean), and enough dust flung into the atmosphere to dim the Sun and kill off vegetation. That could ruin your day.

Comets, Meteors, and A... Seymour Simon Best Price: $0.10 Buy New $3.20 (as of 10:41 UTC - Details)

Then there’s the "Big One". About every 100 million years, a rock the size of a small asteroid slams into the Earth, causing global earthquakes, kilometre-high tidal waves, and immediately killing all large land animals. Creatures in the sea soon follow, as trillions of tons of vaporised rock cause drastic cooling and the destruction of the food chain based on photosynthesis. There’s good evidence that this happened 65 million years ago and our tiny mammal ancestors were the beneficiaries as the giant lizards were extinguished.

The Mystery of 2012: P... Gregg Braden Best Price: $0.10 Buy New $3.49 (as of 04:10 UTC - Details)

A hundred million years sounds like a safe buffer, but the next one could happen at any time. But you can take it off your worry list – astronomers have it covered. A network of ground-based telescopes scans the skies for bits of rogue rubble larger than a few hundred meters. That’s ample time to dust off the nuclear arsenals for an interception mission if we had to. Unfortunately, the Dr Strangelove approach creates lethal shrapnel travelling in the same direction as the original object; a smarter strategy is to send a spacecraft alongside it and gently "tug" it with gravity onto a slightly different trajectory.

When massive stars exhaust their nuclear fuel, the result is a titanic explosion called a supernova. The dying star brightens to rival an entire galaxy and emits high-energy particles that can destroy the ozone layer of a planet like Earth if it occurs within 30 light years. The demise of large North American mammals 41,000 years ago has been linked to a supernova, and several other mini-extinctions may be tied to the cataclysm of stellar death.

A supernova is a small squib compared to a hypernova. In this dramatic and rare event, the violent collapse of a very massive star ejects jets of gas and high-energy particles at close to the speed of light, and for a few moments the star outshines the entire universe in gamma rays.

If a hypernova went off within 1,000 light years, and Earth was within the narrow cone of high- energy radiation, we’d experience an immediate global conflagration. It’s brutal luck if a hyper nova ever goes off with its beam aimed at us.

Read the rest of the article

June 22, 2010