Can we know about every space rock?

The meteor event in Russia on Friday is a sobering reminder that space is a busy place, and that space rocks can take us by surprise. It stands in stark contrast to asteroid 2012 DA14, whose attention-grabbing but harmless pass on Friday evening GMT had been accurately predicted for months. But take note of its name. Near-Earth objects like these have for a number of years been named starting with the year of their discovery; we only found out about this Olympic-swimming-pool-sized rock kicking around in our cosmic neighbourhood a year ago. A month before that, one called 2012 BX34 whizzed by at a distance of 65,000km (41,000mi) - that one had only been discovered two days before. And a few years before that, an 80-tonne space rock called 2008 TC3 ploughed into the Earth's atmosphere, largely burning up and scattering fragments over the Sudan - just 20 hours after it was discovered. The list goes on. The point is that astronomers say that we don't know anything about 5 or 10% of the near-Earth asteroids that are larger than 1km in size - 20 times larger and radically heavier than this week's visitor. That's possible civilisation-ending stuff.

 By Jason Palmer /BBC News /more