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Best way to stop a killer asteroid? Form a committee

The United Nations (UN) has adopted several recommendations of a new asteroid defence plan, the first steps in preventing Earth from being struck by an asteroid. The recommendations were a response to…

It sounds like sci-fi, but Earth could be in an asteroid’s path. Now the UN is doing something about it. Russ Seidel

The United Nations (UN) has adopted several recommendations of a new asteroid defence plan, the first steps in preventing Earth from being struck by an asteroid.

The recommendations were a response to an asteroid strike earlier this year in Chelyabinsk, Russia. This object injured thousands and was around 17 metres across.

Something ten times bigger exploded over a remote Siberian region called Tanguska in 1908. This flattened thousands of square kilometres of forest like matchsticks, with a force hundreds of times that of the Hiroshima atomic bomb.

We have only found 1% of these “killer” asteroids, meaning there are hundreds of times more out there than we know of. One of them, sooner or later, will have our name written on it.

A little disappointingly for fans of Bruce Willis' Armageddon, the UN’s first steps included setting up committees. These will share information about any incoming asteroids (the International Asteroid Warning Group) and decide who will coordinate Earth’s response (the Committee on the Peaceful Uses of Outer Space).

It may not sound like much, but this is in fact a big deal. One of the longstanding issues in dealing with an incoming asteroid was the legal implications of what happens if it goes wrong.

Simply put, if NASA realised the asteroid would hit the USA, and managed to only change the asteroid’s direction to avoid the States but hit China, this could be seen as an act of war (or the mother of all lawsuits at the very least).

For a global threat we need a global response, as well as a global share of the blame if it goes wrong.

The hard bit is over?

Now it’s clear(-er) who is to deal with any incoming asteroids. That leaves the “simple” matter of finding the asteroids and deflecting them.

Asteroids are small, about the size of a football field (of any footy code), which is tiny by astronomy standards. This isn’t a search for a needle in a haystack. It’s a search for that needle somewhere in all the hay on Earth.

It’s hard to spot an asteroid… NASA's Marshall Space Flight Cente

To make matters worse the needles aren’t nice and shiny; they’re dull and barely visible. The only time asteroids are seen by our telescopes is when they reflect sunlight. That means we are completely blind to them if they are coming from the direction of the Sun (although a privately-funded space telescope called Sentinel will lie within Earth’s orbit so all asteroids heading towards the Earth would be lit up by the Sun).

In practice, we find asteroids by taking pictures of the night sky a few days apart; we then play a cosmic game of “spot the difference”. If anything has moved relative to the background stars it must be close to us.

We can then watch the asteroid’s movement over time, getting an ever-clearer idea of its trajectory (or its path through the Solar System) and whether the Earth may pass through it sometime in the future.

We can’t ever perfectly know the trajectory, but we can give a chance of this collision occurring. The UN committee will decide how bad the odds have to get before Earth has to do something about it.

Incoming asteroid, call Bruce Willis?

Once we find an asteroid our options in dealing with it will change depending on how much warning we have.

If we found it early, and have decades to deal with the threat, then it’ll be much easier than if we have only a year (although if it’s too big then we may have no choice but to bunker down and wait out a year for the Deep Impact-style hit).

This is the kind of thing we’re trying to avoid.

Although Hollywood would have you believe otherwise, we don’t want to stop the asteroid (it’s moving too fast and is too massive to even bother trying). We definitely don’t want to blow it up (that would turn a bullet into a shotgun blast that still mostly travels in the same trajectory).

Instead we want to gently nudge the asteroid so that it just misses Earth. The earlier we catch it, the more gentle we can be.

To nudge an asteroid we have two options. The first is to fly a spacecraft beside the asteroid and either throw a bag (or rope) around it and tow it with spacecraft’s rockets. Unfortunately the asteroid may be more a pile of rubble than solid rock and could break apart.

This is why a second option might be better - a gravity tractor.

Just as the Earth pulls you towards the ground thanks to gravity, you in turn are pulling the Earth towards you. But because you’re much smaller this has no noticeable effect.

If we fly our spacecraft beside a larger asteroid, it will fall towards the surface of the asteroid, but the asteroid will have fallen towards the spacecraft by a tiny amount too.

This means that if we then use the spacecraft rockets to back away we can let them fall together again. Do this for long enough and even a giant asteroid will be “towed” by the gravity of our little spacecraft.

To protect humanity from the fate of the dinosaurs, we will need new telescopes to search the skies, and spacecraft technology to perfect the deflection of the asteroid once found. But, to misquote a famous astronaut, even though the UN committee may be one small step for man, it is a giant leap for mankind.

Join the conversation

13 Comments sorted by

  1. Michael Sheehan

    Geographer at Analyst

    It will be committees like these who finally give the green-light to bombing the stratosphere with sulfur dioxide.

    1. Greg Adcock


      In reply to Michael Sheehan

      I really enjoyed this article and the associated links right up until the first comment.

  2. Rene Oldenburger

    Haven't got one

    With other words the astronomy departments want more funding

    1. Greg Adcock


      In reply to Rene Oldenburger

      No it isn't. Why bother replying with something so lacking in substance but high in cynicism and devoid of information?

    2. Rene Oldenburger

      Haven't got one

      In reply to Greg Adcock

      Devoid of information??

      To protect humanity from the fate of the dinosaurs, we will need new telescopes to search the skies, and spacecraft technology to perfect the deflection of the asteroid once found.

      Case closed

  3. David Maddern

    logged in via Facebook

    The idea of blowing one up could be done with a properly formulated device nuclear device that vaporises the thing, not split it into a shotgun blast

    1. Alan Duffy

      Research Fellow at Swinburne University of Technology

      In reply to David Maddern

      It's possible, although I think the best response is likely the easiest one...
      The energy required to split apart an asteroid which would then sail by the Earth (aka the Armageddon plot) is enormous. Students at Leicester worked out it would take billions of the biggest nuclear weapons ever created to simply split it apart, much less reduce the entire object to dust (the paper is here ).

      For much smaller asteroids we could indeed potentially blow them up (resulting in a mess of now radioactive fragments hitting Earth) but most asteroid defence plans using nukes would set them off on the side of the asteroid, pushing it off trajectory and hopefully avoiding the Earth.

      The problem is this is difficult to control / predict, and in any case pieces of the asteroid may still end up hitting Earth. This is why a controlled push from a satellite is favoured by the defence community.

    2. Jeremy Culberg

      Electrical Asset Manager at Power Generation

      In reply to David Maddern

      From my perspective, the idea doesn't have to be to get the asteroid to miss, but simply to be broken up in to chunks small enough to burn up in the atmosphere. It may require multiple nukes, being put at what might be considered fracture lines (and probably drilled in).
      It'd be difficult to get your explosive locations correct though in a low gravity environment, with equipment probably never used for that purpose ever before (etcetera), with fairly low knowledge of the structure of the asteroid.

    3. Alan Duffy

      Research Fellow at Swinburne University of Technology

      In reply to Jeremy Culberg

      In this case, the entire object's energy (which might be thousands of Hiroshima level blasts) is distributed over a hemisphere then that might work. Except of course as you mention the fragmentation might not be perfect, and in any case you've dumped a lot of radiation into the atmosphere which is far from desirable.

      As with disease, prevention is better than the cure.

  4. Michael Lardelli

    logged in via Facebook

    This asteroid-worry is just another of society's petty distractions while other far more important threats are ignored. For example, supervolcano explosions occur far, far more frequently than major asteroid impacts. Since the world's food production system is already straining to feed the current populations and food stocks are dropping, if there was a supervolcano explosion tomorrow we would see world economic and population collapse since it would reduce agricultural production world-wide. The only real question is what will cause a collapse rather than if it will occur. Since oil production will be decreasing by the end of this decade it would seem more likely that energy decline will do it rather than a super volcano. But you never know.....

    1. Jack Arnold


      In reply to Michael Lardelli

      Hi Michael, John Howard (sacked Liberal Coalition PM) accepted your argument completely ... and cancelled all Australian asteroid research projects because by the time the asteroids were identified it would be too late to do anything

  5. Graeme Stenton


    Can we at least get Bruce Willis on this committee?

  6. Fred Moore


    This furphy won't fly.

    We have less than 20 years of "free-energy" OIL (Oil that gives more energy than is put into finding and getting it to market). After that 8 billion people WILL kill each other for what's left.

    Does anyone really believe that on the slimmest chance of a CI (Cosmic impact) we are going to drop our Smart Corporate Greed World posturing and turn into Dumb Corporate anti-meteor slaves?

    Given the trickle up Corporate Oil wars we certainly will have to endure within 20 odd years, A Nice Quick CI would, for most modern minds, be just "To Die For".

    This BS smells like Murdoch.

    What did Rocky say when he came back from the Vietnam MIA furphy In First Blood Pt 2? Oh Yeah. " I'm comin' to get YOU Murdoch"