Is this really the best way to deal with an asteroid?

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Margrave
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Is this really the best way to deal with an asteroid?

Postby Margrave » Tue Mar 14, 2017 11:49 pm UTC

In Armageddon and Deep Impact, an asteroid is headed towards Earth, so astronauts blow it up with nuclear weapons.

First of all, is there even enough nuclear megatonnage in the world to blow up an asteroid large enough to threaten an extinction-level event?

Second, if there is, and the mission succeeds, now we have a cloud of fragments of the same aggregate mass and kinetic energy as the asteroid, heading for Earth on the same course with the same velocity, only now they're radioactive.

Perhaps a bunch of nukes could be detonated at some point on the asteroid's surface -- not to destroy it, but to alter its trajectory away from Earth. Would that work?

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Re: Is this really the best way to deal with an asteroid?

Postby Deva » Wed Mar 15, 2017 12:33 am UTC

Assumes an asteroid of ten to fifteen kilometers. Chooses Castle Bravo as the warhead. Created a crater two kilometers long and seventy-six meters deep. Expects different material composition, of course.

Seems insufficient alone. Presumably affects its trajectory, however. Pushes it (and any fragments) away from Earth. Cannot guess by how much. Depends on the firing range too. Requires a more significant deflection at short range.
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Re: Is this really the best way to deal with an asteroid?

Postby Weeks » Wed Mar 15, 2017 4:12 am UTC

Title sounds like a newspaper headline (and the answer is no, per Betteridge's law)
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Re: Is this really the best way to deal with an asteroid?

Postby Angua » Wed Mar 15, 2017 7:04 am UTC

Wouldn't a cloud be better though, because they'll burn up in the atmosphere? Get a great shooting star show though.
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Re: Is this really the best way to deal with an asteroid?

Postby AngrySquirrel » Wed Mar 15, 2017 9:31 am UTC

If I've learned anything from anime and manga it's that you need to punch it.
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Re: Is this really the best way to deal with an asteroid?

Postby Soupspoon » Wed Mar 15, 2017 10:11 am UTC

Best to discover the ELE three or four solar orbits before the intersection event, if we can. Use one full solar orbit to get as precise a measurement as we can on its terminal impact details, whilst developing both a delivery system and a payload (or selection of payloads).

With (at least!) two or three orbits left in its repertoire, we hopefully now know what it's doing, and what we can do. Allow a full orbit for our Earth-launched system (into a suitable solar orbit) to edge over onto the orbit of the offending bit of rock (and/or ice, as we will have no doubt narrowed it down, accordingly, in the interim), though we may need to only wait half the orbit if wevare lucky, depending on various factors. Then we deploy the payload(s). Mylar sheeting or titanium powder to increase its rsflectivity, or carbon dust to darken it, might be spreadable across the surface to alter the photonic pressures in the right direction to engineer a miss. Or grapple the object (huge 'net'? More robust 'harpooning' device?) and deploy a solar sail out the other side of the craft. Soft-land an ion-drive, to be powered up whenever the spinning object presents the upward-facing nozzle towards a useful hemisphere of the heavens.

Or perhaps something nuclear 'airbursting' could nudge things. Do it far enough way to merely ablate your target to provide the 'nudge' (or nudges, maybe you send a series of devices, for both backup purposes and 'a little bit often'ness), rather than actually shattering it.


Or send people up there to dig out a city and kick start the asteroid-mining revolution by learning quickly, with their own pressures to succeed, and hope that nobody gets the bright idea to move themselves off-trajectory, whilst leaving a huge plug of waste material heading even more inevitably upon an intercept course with 'dear mother Earth'... ;)

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Re: Is this really the best way to deal with an asteroid?

Postby Zohar » Wed Mar 15, 2017 12:56 pm UTC

Isn't the plan in pretty much both of those movies to break the asteroid apart and affect the individual pieces' course so they don't hit the Earth? Also they don't succeed in completely avoiding it in Deep Impact.
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Re: Is this really the best way to deal with an asteroid?

Postby somitomi » Wed Mar 15, 2017 8:27 pm UTC

Angua wrote:Wouldn't a cloud be better though, because they'll burn up in the atmosphere? Get a great shooting star show though.

I think the problem with the cloud is (assuming most of it hits Earth) that it still delivers the same amount of energy the original big rock would, just in a slightly different way.
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Re: Is this really the best way to deal with an asteroid?

Postby Angua » Wed Mar 15, 2017 8:51 pm UTC

Surely it's the impact with the ground that's the problem though? Not the worry about it knocking the planet off course or something.
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Re: Is this really the best way to deal with an asteroid?

Postby LaserGuy » Wed Mar 15, 2017 11:09 pm UTC

Margrave wrote:In Armageddon and Deep Impact, an asteroid is headed towards Earth, so astronauts blow it up with nuclear weapons.

First of all, is there even enough nuclear megatonnage in the world to blow up an asteroid large enough to threaten an extinction-level event?

Second, if there is, and the mission succeeds, now we have a cloud of fragments of the same aggregate mass and kinetic energy as the asteroid, heading for Earth on the same course with the same velocity, only now they're radioactive.

Perhaps a bunch of nukes could be detonated at some point on the asteroid's surface -- not to destroy it, but to alter its trajectory away from Earth. Would that work?


No, this isn't the best way to deal with an asteroid. This may be the best/only way to deal with an asteroid on a collision course that's going to hit us really, really soon (say, in the span of a few months, even <5 years). If we have a longer period of time, then there are better ways that we can use to deflect its trajectory, since we don't need to move it as much--just nudge its trajectory a bit and it could miss us by a thousand miles.

That said, I suspect that a single nuclear weapon is probably not going to do much to a very big asteroid. OTOH, we have a LOT of nuclear weapons at our disposal.

FWIW, the gravitational binding energy is given by U ~ GM^2/R. If we assume 10 km radius, with a mass of 10^17 kg (on the higher end of estimates for the Chicxulub impactor), then the binding energy works out to 10^23 J... which basically means we're screwed, since that's ~10000 gigatonnes of TNT equiv. If it's on the lower end of the mass estimates, 10^15 kg, then it's about a gigatonne of TNT--about a sixth of our global nuclear arsenal. So theoretically, at least, we could obliterate it.

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Re: Is this really the best way to deal with an asteroid?

Postby Soupspoon » Wed Mar 15, 2017 11:16 pm UTC

Angua wrote:Surely it's the impact with the ground that's the problem though? Not the worry about it knocking the planet off course or something.

One 20 metre rock that never hit the ground.
Another, 3-10 times the size, that airburst.
So how effectively can we really fragment a 1km rock or bigger?
Something 350m in size might be Ok, though... Good job it's no longer of concern. (Nor anything else we know about... know about.)

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Re: Is this really the best way to deal with an asteroid?

Postby Angua » Thu Mar 16, 2017 6:59 am UTC

I'm not disputing that fragmenting it will be difficult. I'm disputing that if we did have a magical way to fragment it to a 'cloud of fragments of the same aggregate mass and kinetic energy' that that would not be useful in the 'avoiding an extinction level event' sense.
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Re: Is this really the best way to deal with an asteroid?

Postby gmalivuk » Thu Mar 16, 2017 2:21 pm UTC

Angua wrote:I'm not disputing that fragmenting it will be difficult. I'm disputing that if we did have a magical way to fragment it to a 'cloud of fragments of the same aggregate mass and kinetic energy' that that would not be useful in the 'avoiding an extinction level event' sense.

The Chicxulub Impactor likely had about 5e23 J of kinetic energy. Earth has about 5e18 kg of air with a specific heat of about 1 kJ/(kg.K). So that energy, delivered directly and evenly to the whole atmosphere, would warm it up by 100 K.

I think the ground impact was actually quite a bit less devastating than that.
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Re: Is this really the best way to deal with an asteroid?

Postby Angua » Thu Mar 16, 2017 5:40 pm UTC

Fair enough
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