I don't understand the whole 'we don't want to break up a loose conglomeration of rock'. I'd actually think breaking an asteroid up into multiple pieces that can be 'eaten' by the atmosphere would be easier/safer? The atmosphere does a good job of destroying smaller stuff. Breaking stuff up and letting it burn up seems much more feasible then trying to calculate the exact method to hit an asteroid without fragmenting it and still generate outgassing/thrust ?
> I don't understand the whole 'we don't want to break up a loose conglomeration of rock'. I'd actually think breaking an asteroid up into multiple pieces that can be 'eaten' by the atmosphere would be easier/safer?
Energy.
A large enough meteor impacting the Earth at speeds high enough to cause an extinction-level event has a lot of kinetic energy.
Intuitively it seems like the troublesome part is the meteor hitting the Earth and causing earthquakes, tsunamis, and clouds of ash and debris as a result. And those things are really bad. But they’re a consequence of that mountain of kinetic energy.
So you break the asteroid up into a cloud of dust. Fantastic! No more crater, no more big boom. But you still have a giant ball of kinetic energy headed right at you, and that energy is just going to dump into the atmosphere. And boil it.
Of course that’s even assuming we totally vaporize the thing. More likely is instead of one multi-mile asteroid we have a bunch of giant chunks that will spread death and destruction all across the side of the planet unlucky enough to be facing it… before boiling the atmosphere anyway.
That seems like it would require an absolutely huge amount of matter, given what's happened after old impacts or large volcanic eruptions. Would we realistically have enough nukes/energy on hand to divert something that massive? It just seems like an incredibly difficult way to do it?
P.S.
I you fragmented an asteriod - would at least _some_ of the pieces tend to change heading/speed enough so they miss earth?
The idea is that you catch them far enough away in time so that a small nudge pushes them enough to miss.
Far away in time doesn’t even need to mean far away in space, since many of the objects of concern are orbiting the Sun along with us. They may even have multiple close passes before being perturbed enough to become a threat.
Also, the masses involved don’t have to be huge. Two rocks intersecting in space are likely to be doing so with very different velocities. Kinetic energy is mass times velocity squared, so velocity rapidly overtakes mass as the dominant factor.
P.P.S.
Hmm - actually, if the object is that big...would we even have enough nukes/energy to break it up. Seems like either way (breakup/push) we're going to be limited by the amount of energy we can deliver compared to the mass of the asteroid? Oh! also, would a nuke actually keep stuff out gassing long enough before it cools back down? how long would you need to have that tiny lil push going on before it made any practical difference? thats a lot of mass to try and push ??
These aren't numbers, but a quick intuition reminder: nuclear-powered ablation drives are really good and we are really good at building them.
That's how you turn a fission bomb into a fusion bomb. If you just put LiD in a fission bomb, it doesn't squeeze hard enough. If you focus the x-rays from a fission bomb onto an ablation drive, it does squeeze hard enough and you 1000x+ the yield with fusion. Which is why fusion bombs look like metal peanuts.
Conveniently, this means we are also really good at designing x-ray reflectors and lenses that focus the primary output of a nuclear bomb for the purposes of building ablation drives. Depending on just how good, we could probably persuade an asteroid pusher to be far more unidirectional than one typically pictures from a "bomb," if we set it off some distance away and focused the x-rays in the direction of the asteroid.
Thanks! It actually appears it requires a lot LESS energy then I expected. According to [1] less then a tonne of TNT could accelerate 1 million tonnes to 0.1 m/s !! So it appears I was WAY off base (by at least 10^6 :-P). I swear I'm a better programmer then physicist!! :-D
I guess it depends on how big the pieces are. If you break a very large asteroid in 3, still large, pieces that might not be an improvement. A nuclear weapon exploding in a vaccum is likely to be a lot less destructive than one exploding in the atmosphere.
Enough energy is going to be dumped into the atmosphere either way it doesn’t make much difference. Further, even fist sized fragments are going to penetrate deep into the atmosphere so all options are effectively ground level detonations.
Suppose over one second you can be hit the earth with with either 1 30 gigaton weapon, 3 10 gigaton nuclear bombs. 3,000 100MT weapons, or 3 million 10 KT weapons etc. All of those suck in ways that are hard to comprehend.
Given multi-kilometer asteroids like mentioned above, I'm starting to think neither method (fragment/push) sounds viable. The amounts of energy required just seem off the scale? Maybe pushing (multiple?) smaller but still massive enough to have decent kinetic energy into its path would be more feasible. Sorta like pool balls bouncing off each other..I generally end up missing the pocket (earth) when that happens :-)
yeah - how do you keep it out gassing long enough to hit 0.1 m/s though? I would imagine you'd need to nuke it every couple of days or say every week to keep it out gassing long enough to generate that big a change speed?
Hmm - I guess not! According to [1] it would take less then a ton of TNT to accelerate 1 million tonnes (eg like asteroid 12932-zephyr) to 0.1 m/s...So its probably a good thing I'm not responsible for these things!
Let’s go to the extreme and think 10 km wide ball of sand.
Normally when a single bit of sand hits the atmosphere it dissipates energy in every direction. So you a tiny fast moving glowing dot radiating energy in every direction. However you can’t dissipate energy when you’re right next to another particle at the same temperature. Thus energy from each bit of sad can basically only go in 2 directions down or up and you’re not transferring energy through the entire thing before a crust of plasma followed by ~10km wide ball of sand hits the surface.
Hell it could be a ball of water that size and the same basic effect kicks in.
Spread a 10km wide ball of material into a 1,000 km wide diffuse cloud and you are basically slapping the earth with 1,000 km wide disk with an average width of ~17 cm (maximum width ~1m) going 10’s of thousands of km/h. Again things don’t go well, you may be shifting how many minutes various people survive but it’s not actually addressing the issue.
