How Would We Save the Planet from a Killer Asteroid?

By Korey Haynes | November 19, 2018 12:48 pm
fireballs streak across a night sky

Meteors are both common and beautiful. But larger impactors can cause devastating harm. (Credit: NPS)

We don’t need to be scared of everything that falls from space. In fact, literal tons of space rocks rain down daily, though that’s mostly in the form of minuscule dust grains. But every 100 million years or so, catastrophe strikes in the form of a rock spanning miles.

The last one killed not just the dinosaurs, but three-quarters of all life on Earth. The effects on humans could be equally devastating — bomb shelters wouldn’t cut it in the face of such an event.

Not when the shaken Earth hurls tsunamis onto every shore. Not when volcanoes explode in angry retort. Not when the skies go dark with the asteroid version of a nuclear winter, dust and debris covering the sun. Even people who survive the first wave of destruction would inherit a world utterly destroyed. The world’s stubbornest creatures, the cockroaches and rats and tardigrades, would probably be fine. But the rest of us are doomed.

It’s a cataclysm of almost unthinkable proportions, but history tells us that it is indeed possible. Thankfully humans today have rockets and nuclear bombs and NASA. We can engineer a way out of this.

Stop That Asteroid!

Back in 1998, Congress tasked NASA with identifying these killer asteroids, and expanded their demands in 2005. As it stands, by 2020 NASA is supposed to have identified 90% of asteroids 450 feet or larger — and they’re making good progress on that. So let’s assume we can spot an asteroid hurtling toward us — what’s the next step?

It turns out we have options, but our best bet is never to blow up the incoming object. Destroying a massive rock miles across is difficult work, and in the best case, you still end up with a cloud of small debris, which could still pose risks. So experts focus instead on nudging these asteroids out of Earth’s path.

Again, we know where most of these objects are. If they’re coming our direction, we’d likely have years of advance warning. And space is large and empty enough that a gentle nudge should be all that’s required to save the planet.

tiny dots swirl in circles, with planetary orbits labeled

NASA’s Near Earth Object Observations Program tracks asteroids. This is all the known objects of as January 2018. (Credit: NASA/JPL-Caltech)

Going Nuclear

Nuclear weapons are generally considered a move of last resort. They’re also technically banned by the Outer Space Treaty of 1967, but most people assume if the alternative is planet-wide destruction, the treaty can be ignored. And despite what the movie Armageddon may have described, you wouldn’t have to drill into the oncoming asteroid in order for a nuclear weapon to act as a deterrent. Simply exploding a bomb near the surface of the offending asteroid could be enough to alter its trajectory. This means rockets could deliver a nuclear payload without the need for humans to go anywhere near the impactor.

Large warheads can weigh up to a ton. But for all that weight, you get an explosion measured in millions of tons of TNT, enough to shift a sizable asteroid. And the behemoth rockets coming online now or in the next few years will be able to carry more than one of these warheads at once. By stuffing NASA’s SLS to capacity, one study calculates you could deflect an asteroid up to 800 meters in diameter.

Ramming Speed

Of course, just pushing is always an option. While less spectacular than a nuclear weapon, a physical shove doesn’t carry the potential of a payload exploding on launch and littering the Earth below with radioactive material, dooming us all anyway.

In this scenario, a space agency could simply run a rocket into an oncoming asteroid. We don’t currently have the rocket power to be as effective as a nuclear weapon would, but it is the simplest approach, which is attractive when you consider the stress and time constraints we’d likely be under should we find a large space rock hurtling toward us.

Gravitational Tugboat

a spaceship flying next to an asteroid

A spacecraft flying next to an asteroid could gently adjust its course due to the spacecraft’s gravitational tug. (Credit: Dan Durda/FIAAA/B612 Foundation)

The wonderful thing about space is that physics becomes a strange and idealized thing. If you imagine trying to tug a multi-million-ton rock out of the way on Earth, it seems nearly impossible. But in space, friction ceases to exist. Bodies move about as dictated by gravity. So, if you put something heavy near an asteroid, you can pull it off track.

This method happens slowly. It would only change the asteroid’s course at a rate of millimeters or centimeters per second per year. So you need a lot of lead time. But should we happen to find a monster asteroid out there heading toward us with a hundred years of lead time, this method is the safest and easiest way to deflect it.

As a reverse tugboat, scientists have also considered ion beam shepherding. This basically means having a spacecraft fly alongside the asteroid and pelt it with plasma, thereby shoving it aside. Of course, the spacecraft needs to be constantly pushing itself closer at the same time, or the “equal and opposite reaction” effect in physics would simply have the spacecraft pushing itself away in equal measure. Much like the gravity tractor method, this is slow but predictable and possible using technology that already exists.

Or, as a simpler version of that idea, other scientists have suggested simply painting an asteroid white to increase its reflectivity. This equates to more photons from the sun bouncing off its surface, and the extra pressure would serve to gradually move it off course.

Dismantling an Asteroid

There are other, more outré methods, as well.

We could blast it with a laser, for example. The goal here isn’t really to destroy the rock (though that would be part of it) but more to shove it with the laser and use the bits that flake off to help further propel the asteroid away from the laser. But since we don’t currently have a giant space laser, this method requires a bit more planning.

Another option is commonly called a mass driver. This takes the “equal and opposite reaction” to its logical conclusion. In its most basic form, imagine a catapult hurling rocks off of an asteroid. Physics dictates that as you hurl small boulders toward the Earth, the asteroid itself will slide away from us.

All of these methods require some advance warning. The good news is that asteroids large enough to end life on Earth are big enough to spot, so we’ll have plenty of time both to panic and to plan.

CATEGORIZED UNDER: Space & Physics, Top Posts
  • Uncle Al

    Earth’s mean orbital speed is 29.78 km/sec. Earth’s maximum radius is 6384.4 km (Mt. Chimborazo). To convert any hit into a clean miss, one need only change the arrival time by at most

    2(6384.4 km)/[(29.78 km/sec)(60 sec/min)] = 7.15 minutes for slowed.
    3.57 minutes if the impactor can be speeded.

    Transforming a bullet into an expanding shotgun blast is really, really stupid. Hurl a few tonnes of tetraethyl lead at the asteroid –
    d = 1.653 g/cm³; bp = 84 to 85 °C @ 15 mm Hg, mp = -136 °C – rupturing the tank shortly before impact. That will deliver a diffuse push by impact ad a more diffuse push during impact heat vaporization. Work out direct vs. sideways push.

    • John C

      Simple enough

    • 7eggert

      The bullet *will* kill. So if you can’t gracefully push it out of it’s path, I’d rather take the shotgun blast – a dozen or a hundred Tunguska events vs. one Chicxulub crater.

      (Or maybe I’d travel to the impact site, it’s a quick and fast death).

  • OWilson

    Now there’s a real human doomsday scenario to be concerned about.

    Where are the “Concerned Unions of Potential Asteroid Destruction”.

    No money to be made off of that we presume! :)


    • fthoma

      Dr Brian May, the ex Queen guitarist, is leading a group of scientists exploring the whole save the Earth scenario. He completed his astronomy PhD after his music career.

      • OWilson

        Thanks for the cite!

  • Cornfed

    IF we have a hundred years lead time, We could mine the asteroid out of existence before it ever hit!
    Aside from that, simple ramming it to slow it down a smidge sounds like a a simple, sensible way to do it. Heck, why not just ease a rocket up to “kiss” the asteroid, then put the pedal to the metal. Push directly against it. Easy!!

    • 7eggert

      If our rockets arrive there, they will be fast and going outwards. The asteroidomet (whatever) will be fast and going inwards. That will be a kiss to remember.

    • kapnlogos

      Most asteroids and comets rotate and the axis of rotation may not allow a simple push in the desired direction. Pushing off the center of gravity will tend to rotate the body. What is elegant about the gravity tractor scheme is it automatically pulls on the center of mass. plus or minus a little for bulges, valleys and density changes.

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    • Tony Palombini

      I don’t think that’s enough monthly income to move a killer asteroid out of our path. You’ll need to make a lot more money than that sweetheart.

      • John C

        Good point, but if we combine that with the cash from one of the fantastic deal for a reverse mortgage now available to qualified seniors we’re golden.

  • Mat

    Several railguns on the moon shooting 40 pounders a high velocity continuously once they see it as a threat. And then once its hit toss more its way to make sure even large fragments of the asteroid are hit. Then just as you think its over the railgun fires some spinning cable lobs to follow the volley to wipe up the smaller debris. Then just when you think its over and your about to reload. Wammo. The earth gets hit by a hidden massive asteroid flying in that was mysteriously blocked from view beside neptune on its way in. Or so it was recorded. In actuality it was because Nole forgot to clean his monitor that day after he had spilt some drops of his capicinofrappemochachokalattewithahalftwitofgoatsmilk. Shortly after it was recorded we all perished from the asteroid devistation.

    • Uncle Al

      One cannot hit astronomical distances with an unguided projectile. Light pressure and solar wind will dynamically eat you.

      • 7eggert

        In “The Moon Is A Harsh Mistress” (Robert A. Heinlein), the railgun (IIRC) is used to launch freighters while a guiding system on them is used to hit NORAD.

  • 7eggert

    I think the best option is to have a transponder and a rocket on each dangerous asteroid as soon as it passes nearby. If that asteroid turns out to be dangerous (we can detect it due to that transponder), we can ignite the rocket.

    (Unfortunately we can’t ask each asteroid to collect it’s transponder and rocket before becoming dangerous.)

    • OWilson

      I think you may be on to something there!

      Implanting (firing) a small tracking chip at each nteworthy worthy asteroid target (size, proximity of orbit, etc) could provide a tech feasible method of tracking potential interlopers, and at least provide time to decide a course of action!

      Instead of the interminable “studies” of “settled science and trillion dollar “solutions” to deal with normal inclement weather.

      But, take away the $trillions in wealth transfer to the third world, there seems little appetite for the U.N. and the other usual suspects, to do something actually useful to “save mankind”!

      Follow the the money! :)

      • 7eggert

        For each Euro donated to Africa, there are two Euro of revenue taken.

        • Mike Richardson

          He tends to get very easily sidetracked, doesn’t he?

          But your proposal is a good one. Basically like tagging and releasing sharks, though asteroids can be far more dangerous. The picture important thing is to identify and keep track of the potentially dangerous ones and provide scientists and engineers the time they need to formulate and implement the best means for addressing the problem.

          • OWilson

            I just said that! :)

            Polly want a cracker?


          • Mike Richardson

            Hello yourself, Oldman.

            Your parrot reference, after posting another one of your own cut-and-paste off topic diatribes, certainly confirms that irony continues to elude you, along with relevance and wit.

            Thank you, by the way, for proving exactly what I said about you in your next reply to 7eggert. You just can’t help yourself, can you? 😁

            The fact is, it was a good suggestion from 7eggert, as are many on this board. The threat of asteroid impacts deserves serious thought. So does climate change, which you sneer at as insignificant and not worth studying. Large asteroid impacts are a low probability but high cost (in terms of lives and property) occurrence, whereas climate change is occurring and accelerating now, with costs which will only increase with time. If we’re thinking about insurance for one, we should be considering it for both.

        • OWilson

          “The government of Zimbabwe (home of genocidal dictator Robert Mugabe, and former ‘breadbasket of Africa’ under white farmers) requires a total of $1,572,009,953 with effect from February to December 2016,” said Emmerson Mnangagwa, Zimbabwe’s vice-president. – The Guardian

          Politics and corruption as usual! :)

          Then there’s my local neighbor Haitii located on the same bountiful and fertlie Island,

          $15,000,000,000.00 in aid disappears!

          “Haiti: Where Did the Money Go” – Wiki

          And, they are just two out of hundreds of basket case third world corrupt countries lined up with their hands out!

          As they say in my well fed and self sufficient DR, “No alimentes a los pájaros, los harás perezosos y enfermos y olvidarás cómo vivir!”

          Politics and corruption: Follow the money, (if you can!) :)

  • William

    A magnetic tractor is another way greatly outdoing the puny gravity tractor.

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  • Erik Bosma

    I’d go with building a huge catcher’s mitt and putting it in orbit around the Earth.

  • Dennis Spirgen

    “We’ll have plenty of time…” Really? An object coming in from outside the solar system like the comet Oumuamua (formally designated 1I/2017 U1) comes in much faster than a solar asteroid, and can come in at a high angle to the ecliptic. This makes them very hard to detect. In fact, Oumuamua was not spotted until it was already on its way out of the solar system. Had it been on a collision trajectory, we might never have known before impact.


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