since moved to the National University of Singapore.">

By Steve Pointing 13/10/2015


There were a large number of people who believed that the end was nigh last weekend, after reports that a massive asteroid was going to pass perilously close to Earth and possibly even impact and cause global devastation Armageddon style. 

The fact that I reported this story on Monday’s Paul Henry Show attests to the fact this did not happen – but what were the facts? And how much of a risk is there really for an asteroid impact?

The US space agency NASA’s Near Earth Objects program (NEO) tracks objects in space, and this is really the only major effort to monitor the risk of asteroid impact. NEO is an umbrella for many projects that use both ground and space telescopes and they have identified an astonishing amount of ‘stuff’ in space. The wide field infrared survey explorer (WISE) satellite has found 21 comets, 34,000 asteroids and 134 near Earth objects since 2009 – and all of these just in the space between Mars and Jupiter in our solar system!

Asteroids become termed a ‘near Earth object’ if they pass within 7.5 million km of Earth (almost 20 times the distance to our moon). If the object is wider than 150m then it is termed ‘potentially hazardous’.

On October 10th (Saturday) a massive asteroid possibly up to 2.5 – 3 km wide passed within 25 million km of Earth, which is not really that close (about half the distance from arth to Mars) and hence NASA claim there was little danger of an impact.  However, if an object of this size did hit Earth the blast would be more than that which would occur by simultaneously detonating all of the world’s nuclear weapons combined.

Big enough to cause trouble?

Asteroids passing us within the near Earth object range are surprisingly common.  This month alone there are 5 other near Earth objects being tracked, most are only about the size of a house but worryingly they will all pass within 1-1.5 million km of Earth.  So are they big enough to cause trouble? The energy stored in a rock traveling at around 65,000 km/h is huge, so even small asteroids can cause devastation if they impact another solid object such as the Earth.  A well-known example occurred in 1908 in Tunguska (Siberia) where a 50m asteroid flattened 2,000km2 of forest (twice the size of greater Auckland) and caused a magnitude 5 Earthquake.

So how big would an asteroid need to be to become a ‘global killer’ and drastically impact life all over the planet? An object larger than 3km in diameter would probably do this, and so Saturday’s asteroid was in the right size range to be scary despite being too far away to be considered a serious threat. Probably the most famous example of such a devastating impact is the asteroid that caused the 10km wide Chicxulub crater in central America. This massive impact is widely believed to have led to the demise of the dinosaurs some 65 million years ago due to the amount of dust and debris released into the atmosphere and the resultant breakdown of global ecosystem function.

Of all known near Earth objects, NASA estimate there is only a 0.01% chance of a single impact in the next 100 years – so ironically we have more chance of experiencing an asteroid impact than of winning Lotto – yet I suspect most people would like to believe they are potential Lotto winners!

Little point in worrying

If a potential global killer was detected on its way to Earth, could we rustle up a crack team of space geologists to blow it up and avoid catastrophe – like Bruce Willis achieved in the movie Armageddon? Probably not and for several reasons: To fragment an asteroid several kilometres in diameter would require a massive amount of explosive force, and this would require a huge nuclear weapon being rocketed on a path to meet the asteroid.

The technology to intercept a fast moving object in space is eminently achievable – just think of the success of Rosetta earlier this year, but a manned mission is unlikely for this as it is logistically difficult to send humans into deep space.  Even if a robotic hero did manage to detonate the asteroid, the danger of many smaller but now radioactive asteroids hitting Earth would still be huge. All in all, there is probably little point in worrying about this.  If a massive and previously undetected global killer was to suddenly appear on a collision course with Earth, it may be that we would have little option but to sit back and enjoy the view!