I’m certainly much more aware of them. I don’t think they’re any more dangerous than they used to be, because we’re living at the bottom of a pond that’s called the “atmosphere”, and apart from the very biggest ones, they’ll burn up in the atmosphere or explode well before they reach the bottom of the pond.
What’s changed over the last few years has been my perception of the solar system. I used to think of it as consisting of 8 or 9 planets going round the Sun in serene circles. Nothing much ever happened: it was all very orderly and predictable. In fact, it was pretty boring.
But with the near-simultaneous arrival of asteroid DA14 and the Chelyabinsk fireball on 15 February 2013, and regular reports (and videos) of other fireballs and other asteroids, I came to realise that the solar system was actually teeming with rocks ranging from a few metres in diameter to a few kilometres in diameter. There are millions of them. New ones are being discovered nearly every day. And these are just the ones that come near enough for astronomers to see them.
Because we don’t know where most of them are. There are millions and millions of rocks in orbit around the Sun, and we don’t know where most of them are.
And so, for me at least, the solar system has ceased to seem as orderly and predictable as it used to be. Asteroid DA14’s full designation was 2012 DA14, and the 2012 bit was the year it was found. So it was found less than a year before it came back round and nearly hit the Earth. And the Chelyabinsk asteroid remained completely undiscovered until it exploded over Chelyabinsk.
Asteroids are rocks which have orbits quite near the Sun, similar to the planets. And most of the asteroids are reckoned to lie between Mars and Jupiter in the Asteroid Belt. If they come from much further out, they’re usually called comets. Pluto’s orbit has a radius of about 40 AU ( 1 AU = distance of Earth from Sun), and comets usually come from beyond that distance. And there are reckoned to be trillions of comets in a cloud – the Oort cloud – that extends up to 200,000 AU from the Sun.
These comets have such long periods that we seldom see them. I saw comet Hale-Bopp in 1997. The previous occasion on which it had been seen was over 4,000 years earlier.
So instead of just having 8 or 9 planets orbiting up to 40 AU from the Sun, my solar system now has millions of added asteroids, and trillions of added comets, and is now 200,000 AU in radius. And we know where less than 0.001% of them are. It’s a zoo.
Bearing in mind that that the asteroid or comet that wiped out the dinosaurs was about 10 km in diameter, comet Hale-Bopp’s nucleus was about 60 km in diameter. It reached perihelion on 1 April 1997. Yet it was only discovered on 23 July 1995, by a couple of amateur astronomers, when it was between Jupiter and Saturn. So there were less than two years between its discovery and its close approach to the Sun. It didn’t come anywhere near the Earth, but if it had, we’d have had less than 2 years to do anything about it. So if there is something on track to hit the Earth, that’s the kind of advance warning there’s likely to be. Maybe a lot less.
So, no, I don’t think asteroids are any more dangerous than they used to be. But I’ve come to realise that they’re far more numerous than I used to believe. And the solar system is a far bigger place than I ever used to imagine. And more or less completely unpredictable. It used to look like a very orderly garden, with planets trundling around well-worn circular paths: now it looks like a unpredictable wilderness, changing from month to month, with streams of dust and rocks criss-crossing it in all directions.
And that’s quite a large change of perception.