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How to avoid an asteroid impact (without calling in Bruce Willis)

How many times have you read a headline about our impending doom due to a “Deep Impact”-style annihilation? In a way it’s not surprising – we have an insatiable appetite for disaster stories, a hunger…

Asteroid impacts make for impressive images and movies, but how realistic is the threat? NASA

How many times have you read a headline about our impending doom due to a “Deep Impact”-style annihilation?

In a way it’s not surprising – we have an insatiable appetite for disaster stories, a hunger Hollywood is all too keen to feed. And, in many ways, an asteroid impact is the ultimate catastrophe.

But today the not-for-profit B612 Foundation will unveil plans to build the Sentinel Space Telescope – the world’s first privately funded space telescope, designed to map the solar system for potentially dangerous asteroids.

We’re almost certain that Apophis won’t impact Earth in 2029 … but it still makes for an impressive video.

One asteroid that received significant media interest was Apophis, a 270-metre-wide near-Earth object that, in late 2004, was given a 1-in-37 chance of hitting Earth in 2029.

Further observations almost certainly ruled that impact out, but indicated a possible collision on April 13, 2036 (an exact date, no less). The chances of an impact are now rated as 1 in 250,000 and falling. Despite what you might read on the internet, we don’t need to worry about Apophis.

But how seriously should we take the threat of an asteroid impact more generally? Very seriously – after all, the impact of a 10-kilometre-wide asteroid at Chicxulub in Mexico is thought to have wiped out the dinosaurs.

And here’s another reason to worry: there are still plenty of “Potentially Hazardous Asteroids”, as NASA calls them, that we haven’t even found yet.

Following research using the NASA Wide-field Infrared Survey Explorer, researchers announced in May that we now know of around 96% of the potentially dangerous asteroids greater than 1km in diameter, but less than 30% of the objects between 100 metres and 1km.

That leaves at least 70% of the objects that could wreak serious havoc on the earth’s surface still unaccounted for. For the more macabre readers, there is even a website that will let you determine the impact of an event. Scary stuff.

Last year in November, an object romantically named 2005 YU55 passed within about 320,000km of Earth. The object is about 300m in diameter, and NASA estimates it would have created a 6.5km-wide crater and a magnitude-7.0 earthquake had it struck land, or a 20-metre-high tsunami had it landed in the ocean.

Not quite an “Extinction Level Event”, but still enough to cause major problems if it had landed in or near a heavily populated area. We had only known about this object for about six years when it swung by last year.

More recently – just two weeks ago in fact – the near-Earth object 2012 LZ1 passed within 5.3 million kilometres of Earth. It was discovered on June 10 at Siding Spring Observatory by astronomer Rob McNaught and was determined to be about 500m in diameter.

That’s not quite the size you’d need before calling in Bruce Willis (see video below), but it’s not far off. Somewhat alarmingly, the object’s closest approach was only four days after it was discovered.

Subsequent radar observations using the 300m radio dish at Arecibo in Puerto Rico revised the object’s size upward to about 1km. Now we’re talking about one of the 4% of previously unknown asteroids that could decimate large swathes of the earth. Worse still, had it been on a collision course, we would have only had four days notice.

The problem seems to be that 2012 LZ1 only reflects 2-4% of the light landing upon it, making it darker than charcoal. Astronomers normally assume an asteroid reflects around 10% of the sun’s rays off its surface.

What impact does this have on the number of big asteroids we’re missing? It’s difficult to say, but my guess is the number goes up.

Bear in mind though that no asteroid has been positively identified as posing a probable threat to Earth. Catastrophic events are very rare: kilometre-size asteroids (which pose a global rather than local threat) impact the earth’s surface every million years or so. We don’t need to panic, but we should be prepared.

So what should we – or can we – do about it? Well, NASA runs the Near Earth Object Program, which helps to coordinate efforts to find and study the asteroids. There are also many amateur astronomers who dedicate their time to following up discoveries from their own backyards. These searches are often collectively known as the Spaceguard Survey.

And since 2002 the aforementioned B612 Foundation has been looking into ways of avoiding a “Deep Impact”-style event. More specifically, they are looking at ways to deflect asteroids away from a collision course with Earth.

The plan isn’t to use the standard Hollywood method – nuclear weapons – but rather to attach plasma engines to the asteroids surfaces to gently steer them to a new trajectory. A velocity change of only 1-2 centimetres per second (cm/s) should be enough.

The B612 Foundation’s soon-to-be-announced Sentinel Space Telescope will hopefully shore up our defences against asteroids, mapping out the current and future locations and trajectories of all asteroids that may pose a threat to Earth.

With greater notice, we may just be able to avoid disaster in the event something is found heading in our direction.

Of course, failing that, we still have Bruce Willis – for now.

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10 Comments sorted by

  1. Gavin Moodie
    Gavin Moodie is a Friend of The Conversation.

    Adjunct professor at RMIT University

    Thanx for this interesting and informative piece.

    Do we currently have the capacity to attach plasma engines to an asteroid's surface to steer it to a new trajectory? It seems difficult. Would an experiment or demonstration be worthwhile?

    Incidentally, I don't think anything 'could decimate large swathes of the earth', but rather something might destroy large swathes of the earth.

    1. Simon O'Toole

      Research Astronomer at Australian Astronomical Observatory

      In reply to Gavin Moodie

      Hi Gavin,

      No we currently do not have the technology, however I believe that various people and organisations including the B612 Foundation are working on it. Their idea is to test it on an asteroid a bit further away that poses no threat.

      On decimate versus destroy... I'd argue that they're synonyms.

    2. Byron Smith
      Byron Smith is a Friend of The Conversation.

      PhD candidate in Christian Ethics at University of Edinburgh

      In reply to Simon O'Toole

      In common usage they are, though etymologically the term "decimate" originates from a disciplinary practice in the Roman army where a group that had displayed cowardice were "decimated", which means one in ten were selected by lot and the rest of the group beat them to death. So originally, "decimate" referred to the loss of only 1/10th of a given population.

  2. John Browne
    John Browne is a Friend of The Conversation.


    "Worse still, had it been on a collision course, we would have only had four days notice."

    And here I was worrying about paying off the mortgage...

  3. Bruce Tabor

    Research Scientist at CSIRO

    Interesting article Simon and thanks for the Earth Impact Effects link.

    You've made no mention of comets - the other major class of object that collides with the Earth from time to time. Knowing that 100% of the >1km NEO asteroids will not impact the Earth in the next 1000 years may only cover half the risk if comets >1km impact the Earth with equal frequency (and greater velocity!).

    1. Jonti Horner

      Vice Chancellor's Senior Research Fellow at University of Southern Queensland

      In reply to Bruce Tabor

      It's a good point, Bruce :)

      Our understanding of the threat from Potentially Hazardous Objects has evolved dramatically over the past few decades - back in the 1950s and 60s, when it was first really acknowledged, the great bulk of potentially dangerous objects known were the long period comets - objects flung in from the Oort cloud (a vast cloud of an estimated 10 trillion objects floating around out to halfway to the nearest star) by passing stars that often have orbital periods of hundreds…

      Read more
  4. Gil Hardwick

    anthropologist, historian, novelist, editor and publisher at eBooks West

    Yes, good piece, Simon, though I'm more inclined to wonder that we are here at all, much less got this far.

    Even if we were exterminated, I'd have to say in compensation that it was good while it lasted . . .

  5. Duncan Steel

    Space Scientist, Author, Broadcaster

    Nice re-write of history.

    Of course the Anglo-Australian Near-Earth Asteroid Survey - based at the institution that is now the Australian Astronomical Observatory - never existed. For the record: It was the first southern hemisphere search and tracking program for NEAs. And Ken Russell (of AAO) and myself didn't serve on the NASA Spaceguard Survey committee (for which I proposed the name). Nor was I the only non-US person on the NASA NEO Interception and Deflection Committee (Los Alamos, January 1992). Nor...

    You get the picture.

    1. Simon O'Toole

      Research Astronomer at Australian Astronomical Observatory

      In reply to Duncan Steel

      Hi Duncan,

      Thanks for your comment. This article was never intended as a complete census or history of searches for Near Earth Asteroids. It's purpose was to look to the future, based on recent discoveries in a slightly lighthearted manner. Apologies if you feel that I should have included your work here, but there simply was not room in an 800 word article to cover everything.