Should we Really Risk Ignoring an Asteroid?

NASA’s cost-cutting measures could literally cost the Earth, warns Maggie Aderin-Pocock.

If you are ever in Arizona with time to spare, make a trip out to its northern desert, travel about 43 miles east of Flagstaff and you will find a large hole in the ground called Meteor Crater. Not such an exciting prospect? Well, when I say large, I do mean large; it’s over half a mile in diameter.

Meteor Crater is an impact zone formed when a huge lump of rock crashed into the Earth’s surface around 50,000 years ago at a speed in excess of 20,000 mph. It is one of many such ancient impact zones that litter the surface of our planet. The news that NASA is considering sending rocket probes to investigate the possibility of such a thing happening today may conjure thoughts of bad sci-fi movies, but it also raises the question: is this really something we should fear?

To answer, let us travel back in time a little. As a space scientist, when I say “a little” I am talking about 4.5 billion years or so, to when the Earth was formed. At that point, the rocky detritus floating in space was going through a process known as accretion, coalescing to form the Sun and planets of our solar system. As the solar system matured, most of this detritus was mopped up by the various planets, leaving a small scattering of comets and asteroids out there. Most of these rocky bodies float harmlessly out in space, but the accretion is still ongoing, and every so often one of those stray rocks is attracted to our planet and there is an impact equivalent to a few megatons of TNT.

My job involves managing the building of large satellite systems, and includes the assessment of any risks associated with the project. For this, we use a very simple formula: the hazard is defined as the potential to cause harm multiplied by the likelihood of that harm occurring (the risk). In the case of a near Earth impact, the probability of occurrence is very limited – fortunately, space is vast and, with only a few objects out there, the probability of one hitting Earth is small. However, if we look at the potential harm caused by such a collision, then things aren’t quite so good. Take a six-mile-wide asteroid, for example.

Something similar hit the Yucatan peninsula in Mexico about 65 million years ago. The energy of the impact of this asteroid was comparable to 100 million megatons of TNT. (The bomb dropped on Hiroshima was 13 kilotons and killed 70,000 people.) The impact destroyed everything within a radius of 250 miles, triggered global tsunamis, worldwide firestorms and massive earthquakes. It left a worldwide layer of dust in the atmosphere that many scientists believe was responsible for the extinction of the dinosaurs. So, in our risk assessment formulae we have very low probability but a possibly very high potential of harm (the end of life as we know it).

In the light of this very rough assessment, NASA’s proposal to send a mission – known as OSIRIS-Rex – to look at the Asteroid 1999 RQ36 would seem a sensible idea. Although 1999 RQ36 is only 560m wide, it has a one-in-1,000 chance of hitting the Earth before the year 2200. This mission is in competition for funding as part of the cash-strapped space agency’s New Frontiers program. If the bid is successful, the mission would launch in 2016 and collect a material sample from the asteroid, the idea being to better predict its future trajectory by understanding its composition. The data collected would also be used to predict the motions of other asteroids.

We may be in an era of austerity – OSIRIS-Rex will cost just under three quarters of a billion dollars – but given the potential impact of these near Earth objects, should such a critical endeavour really depend on the result of a competition? Happily, NASA is not our only hope. The Japanese space agency has already visited the Itokawa asteroid and the European Space Agency (ESA) has plans to rendezvous with a comet in 2014. Perhaps we can ensure that those disaster movies remain fiction.

Maggie Aderin-Pocock

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