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Rocket scientists have a plan to save the Earth from asteroids

Their work raises questions about how many resources should be put towards preparing for unlikely but devastating events.

As any casual fan of the dinosaurs knows, an asteroid hitting Earth could be pretty bad news for its inhabitants.  So it may not be super reassuring to know that NASA has currently counted over 27,000 ‘Near-Earth Asteroids’ (NEAs) whizzing around our planet. The scale of death and destruction these NEAs could cause would depend on both the size of the asteroid and where it hit, and could range from nothing happening at all to the complete destruction of entire cities, continents, and species… including homo sapiens.

Given the potential consequences, for many years scientists at NASA have deemed it prudent to look into ways of stopping Earth-headed asteroids in their tracks. In November 2021 they plan to test out the world’s first ‘planetary defence system’. This will attempt to change a (non-threatening) asteroid’s course by crashing a rocket into it.

But is such a scheme really worthwhile? When it comes to asteroid hits, the odds were ever in our favour. The Earth might be big, but space is bigger, and the chances that any asteroid trajectory will directly meet Earth’s is therefore really quite small. Also small, relatively speaking, is the size of many of these NEAs: 97 percent of NEAs are under 1km in diameter. Big asteroids, like the one which wiped out the dinosaurs (estimated size: 5-10km), are a disaster wherever they land because they do things like cause rapid-scale climate change. But the damage of smaller ones is limited to whatever they land on top of. And with the vast majority of the Earth being taken up by the oceans, and plenty of its land given over to sparsely populated things like mountains and deserts, NASA reckons that even if an asteroid did hit the planet, the odds that it would land in a populated area is only about 5 percent.

So all in all, it’s pretty unlikely that you or your home is going to be kaput-ed by an asteroid. But of course unlikely isn’t the same as impossible. Asteroid impacts are examples of what we call high-impact low-probability events. Given that we live in a world of finite resources, the question that these events often raise is how much time, effort and money we should put into preventing them. NASA’s asteroid-nudging program is expected to cost $69 million, as well as the brainpower of a bunch of clever people. Some would prefer that these resources are diverted towards other, higher-probability problems that are activelyharming a large number of people. Others say that given the whole of humanity could be on the line, it makes sense to be extremely risk-averse when it comes to events like asteroid impacts.

Of course, people will shift along this spectrum of opinion depending on the amount of resources that’s being put into preventing high-impact, low-probability events. Although the millions NASA is putting into asteroid-prevention sounds like a lot of money, it pales in comparison to the amount the world is spending on other things. A single year of funding for the NHS runs to £114 billion, for example. The upshot of all this is that planetary defence against asteroids is currently a pretty popular policy: 62 percent of Americans say they support NASA’s work in this area.

Read our explainer on: opportunity costs

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