The Day of the Asteroids – should we be worried?

“Is it reasonable to spend less on asteroid defence than a footballer’s annual salary?”

Brian Cox - The Human Universe. BBC TV

It has been asserted that an asteroid impact took out the dinosaurs. Will a repeat disaster be sufficient to wipe out Homo Sapiens in like manner? It is perhaps reassuring that Saturday, June 30th has been designated “Asteroid Day” to address any concerns we may have and to allow us to quiz the “experts” as to whether we are taking it seriously enough.

There is, of course, a NASA program to discover and document hunks of interstellar rock that could potentially impact the earth (Near Earth Objects – NEO’s), but despite the fact that these are now known in their thousands, it is difficult to pin down these official programs to any meaningful, comparable, usable estimates of exactly what risk they actually pose. Presumably either because we haven’t done the sums, or to avoid frightening the children, or worse still relying on the official reassurances that everything is in hand and it will be “alright on the night” as Hollywood has demonstrated.

How do we know the risk?

To be fair to the official observers, they have produced the usual red amber green pictures to categorise the risk (The Torino Scale) and graphs to illustrate that these meteors have different masses (surprise surprise!). But where are the quantitative risk analyses to show us how big they are, individually, societally and some kind of risk-benefit basis for how much we should spend to address them?.

Chesley highlights the problems with using this semi-quantitative picture (No object has ever been rated above level 4.) and perhaps it could be better plotted as a conventional Risk Matrix. It also uses a colour code scale: white, green, yellow, orange and red. Each colour code has an overall meaning. But what multiple of Probability and Impact Energy (i.e. The Risk?) does each band represent? 

The recent New Scientist article echoes the party line – don’t panic! It’s the big ones that are the problem and they’re easier to keep track of. So don’t worry chicken little, the sky isn’t going to fall in anytime soon - www.newscientist.com/article/dn27764-dont-fear-apocalyptic-asteroids-youre-safer-than-you-think/is 

The article asks the right questions - How big are the risks? and - What should we spend on them? But fails to give us any answers to justify the complacency.

So how do we know the risk?

Ale et al have produced a comprehensive analysis of the risks using the standard individual risk and societal risk (FN curves) together with an outline comparative cost-benefit illustrations.( www.researchgate.net/publication/313472953_Risk_and_Regulation_-_Risks_we_cannot_afford) but this seems to be ignored by the astronomical risk “experts” in favour of the official NASA pictures.

Societal Risk

To try and address this other gap, the FN curve is set out below

And the expectation risks summarised in the table below

The most pessimistic fatality rate corresponds to Marshall’s estimate of the lethality of explosions,(see the Ale reference for details) being 1.7*10 to the 6 per year.

 A more realistic estimate is between 5 and 500 per year, which is remarkably low, as the total data set includes events which would make the whole of species extinct.

There are two FN criteria lines which are generally accepted as benchmarks worldwide, the Netherlands external Safety Criteria and the UK Health and Safety Executive guidelines.

On this plot the asteroid risk exceeds the criteria by an order of magnitude but is in line with the expected risks from the rest of the natural background.

This is not surprising as these criteria are developed for local industrial activities and not for risks that at least in principle involve events that could exterminate mankind.

Individual Risk

If the meteorite risk is indistinguishable from the natural background, then for small impacts the expected risk looks smaller than that of being struck by lightning. So by definition individual risk from small meteorites is acceptable

The contribution to the average accidental risk on a world scale, therefore, is extremely small: only 0.04% of the accidental death rate is caused by NEOs and the individual risk is of the order of 10-8.

So What?

As far as we are aware, although there is obvious concern and commendable vigilance, there are no formal benchmarks for assessing the risks from NEO’s as acceptable or not. Again, the response is bound to differ markedly between the smaller and more massive objects, with the extinction risk one that one definitely can’t countenance. But what are the realistic actions we should take?

This realisation of the need for pragmatism in the assessment of the implications of the “risk” involved led to the adoption in both Health and safety and environmental regulation of the concept of practicality – we must do what we can. (Alkali Act, Best Practical Means (BPM), As Low As Reasonably Practicable (ALARP), etc.).

Cost-benefit Analysis (CBA) in all its forms has thus come to dominate the debate on managing risks. This need for economic realism in addressing risks has also been forced on bodies controlling, for example, transport and medical risks Here the concept of the value of a human life and more recently even the number of useful life years at risk, have been adopted as criteria for action

For threats from these asteroids, the illustrative estimates produced indicate they need to be treated at least as seriously as other major natural hazards and warrant an informed policy response in terms of precautionary expenditure to reflect the value of lives at risk.

We can use a CBA argument based on the value of a human life. At 500 fatalities/yr. this would indicate that we could justifiably spend up to $500*3E6=1.5Billion a year in research and development to do something about the risk.

Current spending is about $0.5 billion, which is not a negligible figure, but does appear to be in the same region as the ballooning Premier League salaries!

 But clearly how much we currently spend should match conventional responses to risk? On these figures, it should be and is certainly more than a football player’s annual salary, but what is the figure that is warranted or desirable in policy terms?

These considerations are all based on the risk averaged over the foreseeable future. They do not take into account that the surprise discovery of a major (Torino scale 10) object may warrant special attention and additional funding for measures designed for the deflection of such objects that could cause such catastrophic consequences.

The current view from observations by the SENTINEL program seems to be that such objects are not expected to threaten our species in the next few decades.

But wait a minute – “You’ve lost what, Dimitri?”

www.newscientist.com/article/2168844-weve-lost-track-of-more-than-900-near-earth-asteroids/

Now we see it, now we don’t Andrez