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December 07, 2005

Asteroid Strike

From the Guardian news of a possible asteroid strike in the coming decades:

Apophis had been intermittently tracked since its discovery in June last year but, in December, it started causing serious concern. Projecting the orbit of the asteroid into the future, astronomers had calculated that the odds of it hitting the Earth in 2029 were alarming. As more observations came in, the odds got higher.

Having more than 20 years warning of potential impact might seem plenty of time. But, at last week's meeting, Andrea Carusi, president of the Spaceguard Foundation, said that the time for governments to make decisions on what to do was now, to give scientists time to prepare mitigation missions. At the peak of concern, Apophis asteroid was placed at four out of 10 on the Torino scale - a measure of the threat posed by an NEO where 10 is a certain collision which could cause a global catastrophe. This was the highest of any asteroid in recorded history and it had a 1 in 37 chance of hitting the Earth. The threat of a collision in 2029 was eventually ruled out at the end of last year.

Why ruled out?

Alan Fitzsimmons, an astronomer from Queen's University Belfast, said: "When it does pass close to us on April 13 2029, the Earth will deflect it and change its orbit. There's a small possibility that if it passes through a particular point in space, the so-called keyhole, ... the Earth's gravity will change things so that when it comes back around again in 2036, it will collide with us." The chance of Apophis passing through the keyhole, a 600-metre patch of space, is 1 in 5,500 based on current information.

OK, so this particular one was thought to be a threat, is now a great deal less of one and so we can all relax? Well, no, not really. An 1 in 5,500 chance may be fairly small but the damage it would do if it did happen would be fairly large.

Traditionally one is supposed to multiply the chance of an event occuring by the cost of it occuring in order to get the expected cost. If the cost were, just as an example, $10 trillion (not unreasonable BTW), then with a one in 5,500 chance that expected cost would be some $2 billion. We’d therefore be logical (ignoring things like discount rates) in spending up to $2 billion in trying to avoid such an occurence.

The unfortunate part of this calculation is that that one in 5,500 is the chance of this specific asteroid hitting us in that specific year of 2036. When we look at the grander picture, the chance of an asteroid hitting us at some point approaches one. It’s virtually certain to happen (but we don’t know when which means that to be complete, we do have to use discounting but I’m not going to do the math).

I’d use this fact (for it is a fact, not an opinion) as a justification for getting up and out into space. No, not some NASA trip to Mars but simply getting up and out there in a cheap and reliable manner. Perhaps the space elevator or some such. Simply because when this does happen it’s going to be a lot easier to deflect if we’re already up there in numbers.

It’s also worth pointing out that sillinesses like Young Earth Creationism don’t really help. Those who think the earth was created in 4004 BC don’t like to think about things like the iridium layer, impact events and Luis and Walter Alvarez’s work. Something both sad and dangerous as it is precisely that sort of work which shows that asteroid impacts have happened before, with depressing regularity, and there is no reason at all to think that they’re not going to happen again.

December 7, 2005 in Science | Permalink


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Tim Worstall: Asteroid Strike Tim reports on asteroid Apophis, which could collide with Earth in the near future. Initial reports suggested a 1in 37 chance of it hitting Earth in 2029. Further work determined that in 2029, only a close pass will occu... [Read More]

Tracked on Dec 7, 2005 2:57:53 PM


I understand there's been some good research that suggests that small, ion engines- launched sufficiently in advance- could nudge an asteroid off a collision course relatively easily. Sounds promising to me.

Posted by: Andrew Paterson | Dec 7, 2005 10:26:55 AM

Lembit for Prime Minister - he'll save us!

Posted by: James Graham | Dec 7, 2005 11:05:07 AM

hmmmm, if you're going to do posts like this based on how much we should pay to avoid small chances of very disastrous events, it would probably be good editorial policy to put a bit of space between them and the global warming ones. Unless I've missed something and your assumption is that asteroid strikes will be avoided or Mars missions funded by private enterprise?

Tim adds: I’m reasonably consistent in my advocacy of private space missions, yes.

Posted by: dsquared | Dec 7, 2005 11:32:13 AM


have you seen this lot? They seem to have set a date.

What's your assessment of viability?


Posted by: Devil's Kitchen | Dec 7, 2005 11:58:55 AM

A browse through Velikovsky's "World's in Collision" might give some idea of the impacts of this type of catastrophe.

Posted by: Ed Derbyshire | Dec 7, 2005 2:27:45 PM

Could it be steered into Brussels at lower cost?


Posted by: Rob Read | Dec 7, 2005 5:24:02 PM

A little problem with developing the technology to deflect asteriods away from the Earth: it could be used just as easily to deflect them TOWARDS the planet. Nice cheap substitute for current WMD - plenty of bang for the buck there!

But I'm sure we can trust the people who would have control of the system to use it only for defensive purposes - In the same way I imagine the first caveman to invent the club promised only to use it on those nasty sabre-tooth tigers lurking outside the cave . . .

And just to depress you further - it's the comets you need to worry about - not the asteroids. You would expect many years' warning of an asteroid strike. Comets follow completely different orbits and would - in a worst case scenario - give only a few months warning of impact, even if we we watching out for such objects.

Posted by: Peter Watson | Dec 7, 2005 6:35:13 PM

Oi, Rob, some of us are IN Brussels!

Glad to hear any justification for continued space innovation, especially the elevator. Payloads coming down power payloads going up. Profit for free, once the dam' thing's built. Why hasn't private enterprise gotten into it already?

Tim adds: Materials science. You need to be able to spin carbon nanotubes into cable to do it. We’re just learning how to do that.

Posted by: auntymarianne | Dec 7, 2005 7:15:14 PM


This could have an upside.

All the guys on the 'Open University' astronomy shows that one watches at 02.45 could become celebrities..and have to shave and get haircuts.

Posted by: The g-Gnome | Dec 7, 2005 8:13:41 PM

A little problem with developing the technology to deflect asteriods away from the Earth: it could be used just as easily to deflect them TOWARDS the planet. Nice cheap substitute for current WMD - plenty of bang for the buck there!

Two problems. 1) not "cheap" and 2) not exactly what you'd call a stealth weapon.

Posted by: dsquared | Dec 7, 2005 11:05:01 PM