The Economist: How to avert Armageddon?

Worrying about the threats posed by space rocks has traditionally been the preserve of the paranoid. No one doubts that asteroids have hit Earth in the past, with nasty consequences, but because the chances of any such happening in a given year are so low, most people have been content to ignore the risk. Today, however, a meteor was seen streaking through the sky above Yekaterinberg in Russia. It hit the ground, possibly landing in a lake, near another city, Chelyablinsk. It is thought to be the biggest meteor to hit earth in more than a century. The shock wave it caused as it passed overhead, blew out windows and injured hundreds of people. Also today, a 50 meter wide asteroid called 2012 DA 14 is zipping past Earth inside the orbit of some man made satellites, marking the closest shave on record for an asteroid of that size. The pair of unrelated events ought to focus minds, and not just among the small group of astronomers who have been worrying about asteroid strikes for many years. The first line of defense, as always, is knowing your enemy. To that end NASA, America's space agency, has been watching the sky since 1998, trying to detect any chunks of rock whose orbits bring them close to the Earth. These rocks are known as near Earth objects (NEOs). The agency reckons it has now tracked down around 90% of the very biggest NEOs, the "Planet Killers" a kilometer or more across. The asteroid that wiped out the dinosaurs is estimated to have been 7-10km across. These heavyweights account for around 10% of the 10,000 or so known NEOs. Most, like 2012 DA 14, are smaller. This makes them less dangerous, though they would still do a lot of damage, if they were to hit a town or city. It also makes them harder to spot. This week's events give the various NEO -detection efforts involving NASA, the Japanese Space Agency and several universities around the world a good excuse to ask for more money to expand their search. Other researchers, meanwhile, have been pondering what to do, if an asteroid is detected that is indeed on a collision course with Earth. In the science fiction film "Armageddon", Bruce Willis leads a team of drillers who blast a dangerous asteroid apart, using nuclear weapons.