The next-generation weapons which will blast asteroids from the sky – and may save humans from extinction
IF an asteroid struck the Earth, there are no fewer than seven distinct ways it could kill you.
If you're lucky enough to dodge the rock itself, other effects of a strike include gusts so strong that they could wrench the limbs from your body, fiery blasts on par with nuclear detonations and towering tsunamis which could drown entire cities.
If you evade these horrors, you're left to face down a powerful shockwave, avoid burning fragments of ejected rock and survive the earthquakes triggered by the strike.
Asteroids can even wipe out entire species: the dinosaurs were thought to have been done in by an asteroid.
It's a good job then, that Nasa takes planetary defence seriously, even if the chances of a dangerous asteroid collision today are very slim.
Every day, our planet is pelted by asteroids, and every day, they burn up into shooting stars when they enter the Earth's atmosphere - but what happens when we end up on collision course with a space rock too big to burn up?
Russia hit by asteroid more powerful than Hiroshima
If even a small asteroid slips through the net, the effects could be catastrophic.
Just five years ago, in 2013, a 20-metre meteor made it through our atmosphere and exploded 20 miles up over Chelyabinsk, in southwestern Russia.
The meteor, which scientists hadn't been able to detect in advance, burned brighter than the Sun, with eyewitnesses in the frozen region reporting intense heat from the falling fireball.
It exploded with up to 33 times more power than the atomic bomb detonated at Hiroshima, smashing windows and buckling buildings for miles around and leaving 1,500 injured.
AI rockets to blast asteroids out of our way
Many of the brightest minds on the planet, across different space agencies, are trying to come up with ways we can protect our planet - and our species - from strikes like these.
These real life Space Invaders are in the process of creating incredible devices straight out of a science-fiction film, which we can call on as a last line of defence if a dangerous asteroid is detected.
One of our best hopes comes in the form of Nasa's fridge-sized DART (Double Asteroid Redirection Test) rocket, an unmanned craft which is currently in development.
The kamikaze ship, which is set to be tested on an asteroid called Didymos, will pass close to the earth but not threaten it in 2022.
It is designed to barrel into the rock at full speed, hopefully nudging it off-course with the force of the impact.
While a small robotic missile won't be able to send an asteroid flying off into space like a snooker ball, researchers hope it will be able make a small but vital difference to the rock's course.
If this change can be made long before the asteroid reaches Earth, the tiny difference could alter the rock's course by thousands of miles before it reaches us - turning a certain collision into a nervy near-miss.
Another potential weapon against asteroids comes in the form of a high-tech piece of kit called a gravity tractor - a conceptual craft which could be built in response to future threats.
Speaking to Sun Online, Dr Hugh Lewis, an asteroid expert working with the UK Space Agency, explained: "It works by 'hovering' next to an asteroid, causing a tiny, tiny gravitational force to be exerted on the asteroid and changing its trajectory over a long period of time."
Nasa concept clips show how these defences could work, with one video demonstrating how a gravity tractor could theoretically pick up a boulder from one asteroid and use its mass to nudge a more threatening rock off course.
And another, more outlandish suggestion has been suggested by American geophysicist H. Jay Melosh, who wants us to build a giant magnifying lens in space which could melt away an incoming asteroid by channelling solar energy at it.
The first line of defence
The trouble is that a gravity tractor would need to fly alongside a rock for up to a decade before it could have an impact on its trajectory - and we'd also need years to prepare for a DART-style mission to knock an asteroid off course.
This means that early warnings are everything, when it comes to asteroid defence.
Dr Lewis, who heads up of the Astronautics Research Group at the University of Southampton, said: "As a space-faring species, we are actually in a position for the first time in human existence to prevent the impact of asteroids on the Earth.
"Unfortunately, the deflection of an asteroid is not the only challenge – first we have to detect them, and this is an area that needs investment and time.
"At the moment, we have very good knowledge of the big asteroids that threaten the Earth, some knowledge of medium-sized asteroids - bigger than a football pitch - but quite poor knowledge of asteroids that are smaller than that."
At the forefront of our asteroid detection efforts is Nasa's Planetary Defence Coordination Office, which keeps an eye on all potentially-threatening asteroids decades before they can reach Earth.
The organisation works alongside the The International Asteroid Warning Network (IAWN), a global collaboration to improve our ability to detect and track asteroids.
But although international cooperation has allowed us to make incredible strides, Lord Martin Rees, Astronomer Royal, argued last year that governments are not spending enough on asteroid defence, which should be viewed as an "insurance premium" against an apocalyptic collision.
The raw, destructive power of asteroid strikes is largely down the array of deadly impacts just one of these collisions can have.
Dr Lewis explained: "It’s a lot like taking many different forms of natural hazard – earthquake, volcano, hurricane/tornado – and experiencing them at the same time."
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It's no surprise then, that the dinosaurs, despite their size and power, never stood a chance against the cataclysmic meteorite which is thought to have wiped them out.
We may never face another asteroid of the same size, but if we do our real-life Space Invaders should be there to make sure that we don't go the same way.