Earth in the crosshairs: We face perils from space
Asteroids aren’t the only thing that could cause catastrophe — a solar flare might wreak havoc, too, writes MICHAEL HANLON.
Considering the dangers lurking out there, it’s a wonder that our little planet is not in the firing line more often. We are just 150 million kilometres from a star that, while mostly well-behaved, occasionally has temper tantrums that could bring our civilization to its knees. Our solar system is home to a swarm of comets, rocks, boulders and flying mountains, tens of thousands of which are big enough to wipe out anything from a small city to the entire biosphere. And farther out lurk delinquent stars whose death explosions are the largest since the Big Bang. If one of these went off nearby, it would be curtains for all of us.
In fact, Earth can be considered rather lucky not to have suffered a total cataclysm in at least 3.5 billion years — the period during which we have an unbroken record of life existing on the Earth’s surface. Before then, global sterilization events, caused by collisions with huge space rocks, almost certainly took place many times — perhaps once every few hundred years. Each may well have wiped out early versions of life. Then, after one final cataclysmic impact, it was clear sailing all the way.
That was what we used to think, anyway. But in recent decades, it has become clear that our cosmic neighbourhood, in more recent times, has not been as benign as was thought.
In the 1980s, for example, it was confirmed that Earth has been hit several times in its history by objects from space — none big enough to sterilize the planet completely, but a handful packing enough of a punch to change the course of life forever. The most famous of these was our collision with a nearly 10-km wide asteroid 65 million years ago, whose fiery passage into the Mexican coast has been blamed for killing off, or at least delivering the coup de grace to, the dinosaurs.
It is not just rocks we have to worry about. Japanese scientists have uncovered evidence from the study of tree rings that, in the year 775, the Earth was hit by a colossal solar flare. The scientists found a spike in radioactive carbon-14, taken up by the ancient cedar trees they were studying.
In Finland, Ilya Usoskin and his colleagues found an identical spike on the other side of the world. One theory is that this was caused by a nearby exploding star — a supernova — showering the Earth with radiation. The trouble, says Usoskin, was that they could see no sign in the skies of a supernova remnant within the required distance. So the scientists turned to the historical record to see whether there were any clues. The handful of supernovae that have burst into existence in historical times have often been well recorded. But, 1,238 years ago, there were reports not of a brilliant “new star” but — as one English chronicler, Roger of Wendover, put it — of the skies themselves catching fire: “Fiery and fearful signs were seen in the heavens after sunset; and serpents appeared in Sussex, as if they were sprang out of the ground, to the astonishment of all.”
This was, says Usoskin, probably an account of an aurora borealis — the northern lights.
“Anyone who has seen aurorae knows they look like serpents,” the Finnish scientist told New Scientist this week. The conclusion is the Earth was hit by a huge mass of charged particles ejected from the sun.
This was far from a one-off: such flares probably happen every few centuries or so. In late August and early September 1859, the Earth was hit by a smaller flare that had equally dramatic effects. Named the Carrington Event, after the astronomer who documented it fully, the solar storm caused Californian Gold Rush miners to be woken in their tents by the bright northern lights.
The main impact on humans was a pretty light show on the ground: There is no evidence that solar storms of this intensity can damage or affect life directly. But there was also a chilling foretaste of what would happen if such an event were to repeat itself today, for the surge of charged particles had a dramatic impact on the nascent telegraph systems of the world. What author Tom Standage has called “the Victorian Internet” was virtually knocked out. Telegraph wires were short-circuited, copper cables melted, and some operators were given bad electrical shocks.
If a rerun of the Carrington Event were to happen today, it would be cataclysmic: power lines would melt, electrical sub-stations would catch fire, half the world’s telephone grid would be knocked out, telecom satellites would go down, and the Internet would be crippled, maybe for a year.
There would be massive disruptions to food and water supplies, water treatment and distribution, as well as the global banking system.
Just repairing the power lines would take weeks — if an adequate supply of copper could be found. In June, a joint U.K.-U.S. study, led by insurers Lloyd’s, estimated that a superstorm of this magnitude would cost the world $2.5 trillion, and tip the planet into depression.
Yet when it comes to such threats from space, we suffer from profound short-sightedness. Asteroid strikes, for example, are seen as the stuff of bad Hollywood films — or at least they were until Feb. 15 this year, when the Russian city of Chelyabinsk was blasted by a 10,000-ton meteor that exploded at 48,000 km/h about 16 km overhead. The blast, comparable to a small nuclear weapon, caused havoc on the ground, smashing windows and injuring more than 1,000 people, some seriously.
As well as being short-sighted, we are also ignorant. Solar storms in particular are poorly understood. Some are high-energy yet do little damage; other, more modest eruptions can cause chaos, such as the 1989 flare that knocked out the power grid in Eastern Canada.
It is now thought that the biggest — such as the 775 event — may be the result of huge comets colliding with the sun. According to David Eichler, an Israeli physicist at Ben Gurion University, a “sungrazer” comet 80 km wide hitting the sun at 1.6 million km/h would generate enough energy to cause a solar flare that, if it hit the Earth, would be far more severe than even the Carrington Event.