For the past couple of weeks, since Asteroid DA14’s close approach to Earth on 15 February, and the fireball over Chelyabinsk on the same day (about 3:30 am UT), like many people I’ve been wondering if the two events were related – particularly since there were other fireballs spotted around that time (e.g. the one seen over the west coast of the USA the same evening).
The experts, however, seem to have been unanimous in denying any connection. Their reconstruction of the Chelyabinsk fireball’s orbit prior to its impact places it in a quite different orbit than DA14. It was, they say, just sheer luck that two different asteroids, coming from quite different directions, happened to arrive at more or less exactly the same time. In addition, they have pointed out that DA14 was approaching the Earth from below the south pole, and so given that the Chelyabinsk is at latitude 55N°, it was next to impossible for anything coming from that direction to land on Chelyabinsk.
I wasn’t so sure, myself. Four of five years ago, purely as a matter of interest, I wrote a clunky little computer simulation model of the solar system, using planet vectors (position and velocity) from JPL’s Horizons website. I also included a clunky little model of the Earth, complete with outlines of its continents, spinning on its axis.
I say the model is a bit clunky because it’s riddled with divide-by-zero errors which I never got round to cleaning up. Also, the Earth goes round the Sun a day quicker than it should do. In short: it’s not very accurate.
But I thought it might be accurate enough to allow me to find out whether rocks in a fragment cloud around DA14 might have fallen in the Earth’s northern hemisphere. So I got hold of DA14’s orbital vectors for a few weeks before the 15 February encounter, and added them into my solar system model, and found that in my model DA14’s closest approach was two minutes before its recorded closest approach, and at a distance of about 33,800 km from the Earth, about 250 km less than its recorded distance. Which I thought was quite good.
I then created a halo of fragments around DA14, travelling at the same velocity, and looked for ones which hit the Earth. And I found plenty. More or less all the halo fragments that hit the Earth landed in the southern hemisphere, as expected. But a few of them curved round the side of the Earth, and swung in towards it. I concentrated on these ones.
And today I managed to find one (which I’ve named Halo10120) which came down in Mongolia a bit south of Irkutsk, at 46°N. Here’s a screenshot of the Earth, with the fragment (which weighed one metric ton) passing over the Earth at about 12.5 km/s and just grazing its surface (the bit where the red track turns green) before heading back out into space:
This view of the transparent Earth is looking down onto the plane of the ecliptic (the path swept out by the Earth as it travels around the Sun). The continents in the upper half are outlined in black, and on the lower half in grey. The north and south poles are marked with crosses. Chelyabinsk is a dot on the map north of the Aral Sea, and the Sun (way off in the bottom right of the picture) is just rising there. Halo10120 comes up from right to left, more or less from where the Sun is.
As you can see, this impact site isn’t very far from Chelyabinsk, and it’s at almost exactly the same time as the Chelyabinsk event. And the path of the fragment is from southeast to northwest (the Chelyabinsk fireball was rather more east to west than this).
This isn’t a complete reconstruction of the Chelyabinsk fireball, but I think it makes a pretty good case that it could well have been a fragment of DA14.
I haven’t yet managed to find a fragment that got as far north as latitude 55°N, but in one or two cases I’ve managed to reach 49°N. So 55°N is far from impossible.
One of the puzzles of this matter is that all the fireball reports around that time were in the northern hemisphere, and none at all came from the southern hemisphere. And yet, by my own estimate, something like 95% – 99% of DA14 fragments would have fallen in the southern hemisphere of the Earth. Surely, if there was a cloud of rock fragments around DA14, there would have been hundreds of reports of meteor impacts in the southern hemisphere?
But the explanation for this may well be that all of the northern hemisphere sightings were of fireballs that skimmed the atmosphere, and travelled through it at quite high altitudes (about 50 km) for quite long distances, and which would have been visible from a long way away for quite a long time (several tens of seconds). Furthermore, most of the world’s population lives in the northern hemisphere of the Earth, and so there would have been more eyes to see such events.
By contrast, the fragments that hit the southern hemisphere tended to come down more or less vertically, punching through the top 50 km of the Earth’s atmosphere in 4 seconds while travelling at 12.5 km/s, and transferring most of their energy to the Earth, rather than to its atmosphere.
Southern hemisphere DA14 halo fragments would have been experienced as a brief flash, perhaps accompanied by a sound of thunder, and maybe an earth tremor as well. They wouldn’t have been seen by many people – mostly because the Earth’s southern hemisphere isn’t well inhabited.
What does it all add up to? Most likely that almost all the fireballs seen around the world around 15 February 2013 were DA14 halo fragments.
And that’s a bit worrying. The impact of the Chelyabinsk fireball has been estimated as several multiples of the Hiroshima bomb, even if it only injured about 2000 people on the ground.
We live in a world in which it is believed that the greatest threat to human health and longevity is caused by smoking, and drinking, and eating too much.
I think there are maybe some far greater threats around.