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Some time ago NASA announced that a 46-metre wide asteroid was heading for the Earth and at its closest approach would pass by within 27 000 kilometres of us. In cosmic terms that is very close, in fact, too close for comfort - satellites that are in geosynchronous orbit round the Earth (such as communications satellites) are further away than that! The Moon is fifteen times further away! In recorded history (admittedly less than 200 years in the case of this type of observation) no object of this size has ever missed the Earth by such a small margin. If a rock as big as 46 metres across were to hit the Earth, the impact would be powerful enough to erase completely a city the size of (say) New York. And in case you think the odds are good that it would land in the sea rather than on solid ground, you are right - unfortunately such an impact would be even more catastrophic, because the resulting gigantic tsunamis would wreak havoc across the globe, engulfing numerous coastal communities and killing far more people.

A meteorite burns up over Russia on 15 February 2013

Friday 15 February 2013 was determined as the day when asteroid 2012 DA14 would swing past the Earth. Countless amateur and professional telescopes were lined up and ready to observe the historic event. NASA had even planned a live web cast of the flyby for people without access to telescopes. The world waited with bated breath, and not a few of us were thankful that it was going to be a close shave and not a direct hit.

And then, on the same day but BEFORE the asteroid made its closest approach, a massive fireball streaked across the sky above the Russian town of Chelyabinsk and exploded in dramatic fashion. The event was captured by hundreds of stunned onlookers on video and mobile phone cameras, and the resulting shockwave shattered windows and injured more than a thousand people. It truly was a "What the **** was that?" moment - the main asteroid was still tens of thousands kilometres away, so what was this? Another meteor? On the same day? Surely not ... what would be the odds of that happening?

Well, it turns out it WAS another unrelated meteor, smaller than the one that had been announced (only about 17 metres across, apparently), but still big enough to cause considerable damage. It was the largest meteorite to hit the Earth since the Tunguska event of 1908, in which an object about 40 metres across disintegrated in the atmosphere and destroyed over 2100 square kilometres of Russian forest. They seem to have bad luck with meteorites, the Russians ; on the other hand, if your country is five times bigger than any other then I guess you are likely to cop more impacts.

The coincidence that the BIGGEST asteroid close approach ever observed and the BIGGEST meteorite impact in over a century took place on the same day is almost too mind-boggling to contemplate. The odds of this happening are just so enormous that I was left shaking my head in disbelief. Absolutely incredible.

But the most worrying thing about the Russian event was that nobody saw the meteor coming, and even several hours afterwards astronomers round the world were trying to figure out where it came from. That is a serious cause for concern. There are doomsday crackpots all over the world predicting "the end of time" for all kinds of spurious reasons (such as the Mayan calendar "scare" of December 2012), but this meteor strike illustrates a very real threat to life on planet Earth. Meteorite impacts over the past several hundred million years have been the cause of several mass extinctions and there is no reason why this can't happen again. The dinosaurs perished 65 million years ago when a 10-kilometre wide comet hit the Earth, and 250 million years ago an even bigger strike killed off over 95% of all species on the planet. These are sobering facts.

The Earth is surrounded by cosmic junk. In fact, over 15 000 TONS of debris from space hit the planet every year; thankfully, most of this comprises dust-sized particles that burn up in the atmosphere and become visible as "shooting stars". Larger rocks are rare but by no means non-existent. NASA has a programme to catalogue and record all "near Earth asteroids" over a certain size in order to provide us with an advanced warning of catastrophe (although it is debateable exactly what we could do to deflect or destroy a rock several hundred metres across hurtling towards us at 50 000 kilometres per hour), but in the case of the meteor that exploded over Russia there was no warning whatsoever. The first anybody knew about it was when it appeared in the sky.

I suggest that this event should be taken as a warning, and that all governments should co-operate to ensure that any object near enough to hit the Earth and massive enough to cause significant devastation is detected and tracked. And a research programme to develop the capability to deflect and/or destroy such objects should receive some very urgent attention.