The earth can’t be saved in one day. On the other hand, it can be destroyed relatively quickly – by an asteroid impact, for example. For this reason, researchers are searching for ways to repel these projectiles from space.The thought alone is tragic. After many years on his lecture marathon, Al Gore has finally stopped the non- stop race towards climate change. Cameron Diaz has saved the oceans, and Bob Geldof has patiently sung away starvation in Africa. All of a sudden, a killer asteroid is hurtling towards the purged planet, and threatens to lay waste to all these efforts – and a Bruce Willis, who in the film Armageddon swings onto the space particle to heroically blow it up, is nowhere to be seen. A close shave, every 76 years: Halley's CometSo it’s comforting to hear that scientists around the globe are searching for ways to track so-called Near Earth Objects (NEOs), and to eliminate the threat they represent. Around 300,000 perigee asteroids with a diameter greater than 100m are flying through space. A diameter of 50m is enough to break through the atmosphere and do significant damage. All NEOs with a diameter greater than 10 km have already been discovered. This was roughly the size of the asteroid that struck the earth around 65 million years ago, thereby sealing the fate of the dinosaurs.NASA is approaching this problem in a brutal manner, focusing on atom bombs. However these are not to be drilled into the asteroid simply to pulverise it, as was the case in Armageddon. Rather, they want to detonate the bombs close to the planet, the resultant shock waves thereby throwing it out of its orbit.But this can also be done in a softer way. A research team of Massimiliano Vasile, of the University of Glasgow, want to simply eliminate dangerous asteroids with the power of the sun. Their studies focus on the so-called solar concentrator mirror technique: Multiple spaceships are fitted with mirrors of 20m in size, and approach within a few hundred metres of the space particles. Reflectors concentrate the sunlight and throw it onto a point on the surface of the asteroid. There, temperatures can reach up to 2100 degrees Celsius. The rock would then vaporise, while the gases created would send the asteroid like a jet in the opposite direction. Artist viewThis method has considerable advantages over other procedures. “Our studies show that this technology is genuinely feasible and, unlike methods where an explosion or impactor is used to divert the asteroid, there is no further risk from fragments,” says Massimiliano Vasile. The plan, however, sounds somewhat simpler than it actually is. At least 10 such spaceships would be required to throw a 150m asteroid off its earth course. And that would also take some time. “It would take about six months to steer an asteroid of this size into a safe orbit,” says Vasile. Compared to the length of time for which Hollywood and the rest of the world will have to fight climate change, however, that’s not actually all that long. Images: German Aerospace Center