Deflecting an Asteroid Will Be Harder Than Scientists Thought (upi.com)

schwit1 shares a report from UPI: According to new asteroid collision models designed by scientists at Johns Hopkins University, deflecting a large rock headed for Earth will be harder than previously thought. Using the most up-to-date findings on rock fracturing, researchers developed computer models to more accurately simulate asteroid collisions. For the newest study, scientists decided to divide the model into two phases. Phase one modeled the immediate fracturing that happens in the wake of a collision -- the processes that play in a matter of seconds. The second phase simulated the gravitational re-accumulation process that happens over the course of several hours or days.

The first phase of the updated model showed a large asteroid is not destroyed by a much smaller asteroid. Instead, millions of cracks form throughout, the core fractures and a crater is left behind. During phase two, the fractured core exerts a strong gravitational pull on the smaller pieces of debris and shrapnel broken during the impact. Because the asteroid did not crack completely during phase one, the space rock retained significant strength. If scientists are going to develop an asteroid deflection strategy that can actually work, they need to know how much force it really takes to destroy or deflect one. The latest study -- published in the newest issue of the journal Icarus -- showed it's more force than was originally thought.

Comments

Re:Isn't the goal to change its course?

[Antique Geekmeister]

There have been many, very useful analyses of the trade-offs. I've seen many in fiction and science speculative scientific analyses: I remember reading J. E. Enever's analysis in a 1966 Analog magazine article. Given how little was known about the composition of asteroids that had never struck the Earth to be analyzed, and that the article predated the discovery of the dinosaur killer asteroid, it was quite good. Asteroids are high velocity projectiles, and whether they are solid rock, reasonably metallic, or icy makes enormous difference in the results of breaking them up.

Orbital mechanics and basic geography physical chemistry haven't changed much since that period. Guidance systems have improved tremendously, and humanity has learned a great deal about sending small probes to other worlds. But changing the orbital path, or shattering, something as large as a dinosaur killer asteroid is still an incredible engineering problem.

Re:Deflection

[Immerman]

Vaporizing is completely different than shattering. For starters, the remaining asteroid remains intact, while the vaporized rock leaves at high speed as jet engine exhaust. That works great.

Don't kid yourself that the size of the fireball has anything to do with the size of the crater it would produce though. The fireball is just superheated gas expanding through cool air, long after the blast has done its damage - it takes very little energy to produce compared to trying to vaporize or displace rock. Also, to get an appreciable crater you'd need to bury the nuke deep underground so that it blasts material upwards instead of down - similarly to how most of the energy of a meteor impact is delivered well below the surface as rock is vaporized out of its path.

And burying a nuke greatly increases the odds of shattering the asteroid rather than deflecting it. And that's almost certainly a bad thing. You've just turned a predictable rifle slug impact area that could be easily evacuated, into a shotgun blast.that will pepper the Earth with nuclear-size impact blasts. Even if half the material misses the Earth entirely, the total damage would be much greater - the size of an impact crater scales with the cube root of the impact energy (in this case, mass, since all else remains roughly constant). Break an asteroid into 8 equal pieces, and now you get 8 impact craters, each still half the diameter that the original would have been. Break it into 64 pieces, and each crater would still be 1/4 the size of the original. Even if half of them missed Earth, you'd still end up doing far more total damage.

About the only reason you'd want to risk doing that is if it was a *really* large asteroid that was going to hit the ocean, generating massive tsunamis and vaporizing a huge mass water that would devastate weather patterns for potentially years to come, doing far worse secondary damage.

And if the asteroid was that big, then even a Tsar Bomba buried in it's core might not be up to shattering it.

Plus there's the slight problem that unlike rockets capable of delivering it, we don't have any Tsar Bombas just lying around in storage (so far as I know), and building one is going to take time. time we wion't necessarily have, and even if we do, every second we wait to launch brings the asteroid closer and reduces the amount of benefit an explosion of a given size can achieve.