
If We Blow Up an Asteroid, It Might Put Itself Back Together - mykowebhn
https://www.nytimes.com/2019/03/08/science/asteroids-nuclear-weapons.html
======
lisper
The best way to prevent an asteroid from hitting the earth is not to blow it
up but to deflect it using a solar powered gravity tractor.

[https://en.wikipedia.org/wiki/Gravity_tractor](https://en.wikipedia.org/wiki/Gravity_tractor)

[https://b612foundation.org](https://b612foundation.org)

~~~
sandworm101
Or a solar mirror, from afar, to divert it using light. Gravity tractors arent
easy. They need fuel and there are exhaust issues that limit performance
(exhaust has to miss the rock). A bunch of big mirrors can impart
energy/motion without having to stay in a paticular position.

~~~
lisper
Do you have a reference? Has someone actually done an analysis? I've never
heard of this idea before, and offhand it seems impractical. I think you'd
have all the same problems that you have with a tractor, plus a few extras.

You're right that gravity tractors aren't easy. Nothing is easy in space.

------
_ph_
As a simple approximation, debris of an explosion would need to reach the
escape velocity of that asteroids gravity field to permanentely be separated
from the asteroid. To "blow up" an asteroid, one would need a sufficiently
strong explosion to reach the escape velocity for at least a large part of the
debris. The recombination of the asteroid would take quite a lot of time,
considering the weak gravity. So if it is blown up at the right moment,
recombination does not have enough time. Just reducing the density of the
asteroid or rather its cloud of debris beyond a certain point might be
sufficient to prevent a large disaster on earth. It then doesn't matter if the
asteroid would recombine after crossing the earths path.

~~~
sagartewari01
The idea of earth ghosting through a giant rock certainly does sound pretty
cool.

------
topmonk
A very naive question, but could we rotate an asteroid apart? Suppose we
continuously hit it with a laser at an angle, so the resulting heat would
cause a bunch of small explosions and impart angular momentum, until it
rotated so quickly that it simply tore itself apart.

~~~
thereisnospork
Probably not - but it is easy enough to deflect an asteroid's trajectory to
avoid earth. Over astronomical distances simply heating a portion of the
asteroid can provide enough thrust to sufficiently avoid a collision.

~~~
A2017U1
I believe you need enough advance warning and it's actually quite _simple_ as
far as these things go.

Always surprised how little science there is in this stuff, both detection and
diversion it is a real existential threat to humanity given enough time and
yet militaries around the world are out there tilting at windmills spending
all their cash on outdated bloated acquisition projects to kill each other
better in the most peaceful time on Earth.

~~~
sagartewari01
The reason is probably same as the reason toddlers aren't afraid of guns.

------
blaisio
I actually took a class on this stuff in college. Basically, the forces
involved are so tremendous that there's probably nothing we can do to prevent
an asteroid impact. Also, odds are we wouldn't even detect it until maybe a
few days before.

Maybe if we had 20 year's notice, we might be able to do something. But even
then, probably not.

------
nraynaud
Wouldn’t transforming the asteroid from a solid rock to a ball of sand already
be an improvement? 1) it looses density 2) it loses cohesion

~~~
_ph_
It depends. The kinetic energy of the impact wouldn't be changed. The nature
of the impact would be changed though. A pile of sand would probably transfer
its kinetic energy into the atmosphere instead of impacting the ground. This
could be good. But then, setting the atmosphere on fire might not be that
great of an idea.

~~~
darkpuma
If the sand cloud has expanded enough before impact, then a large portion of
it may miss earth entirely and therefore reduce the kinetic energy earth's
atmosphere has to absorb.

~~~
_ph_
As the post I was answering to just talked about converting the asterioid to
sand, I assumed, that all of it would hit the atmosphere. But indeed, if in
this way part of the asteroid misses the earth entirely, it would be a win. I
was also a bit simplifiying/exaggerating. When talking about heating up the
atmosphere, the consequences entirely depend on how high the thermal impact is
going to be. If spread far enough, there could be a "global warming" which is
below the limit for an instant disaster. (And when caused by a single event,
would decay quickly)

~~~
darkpuma
Something else to potentially consider is the spread in the 'z axis', which
would spread out the heating across time, not just space. Although I think
that only helps if there is enough time for Earth to radiate a lot of that
heat.

------
yaacov
> Using computer models, scientists simulated a 4,000-foot asteroid smashing
> into a 15.5-mile asteroid at 11,200 miles per hour.

The biggest known potentially hazardous asteroid is only 7 km in diameter.
([https://en.m.wikipedia.org/wiki/(53319)_1999_JM8](https://en.m.wikipedia.org/wiki/\(53319\)_1999_JM8)).

> The study has limitations. Both asteroids are modeled as simple, nonrotating
> chunks of rock, whereas real asteroids are far more variable. In addition,
> the larger asteroid, despite featuring a starting collection of cracks, did
> not have a history of multiple impacts as true asteroids would.

Sounds like this model was designed to generate sensationalized headlines like
this one.

~~~
simion314
Models are not reality, you exclude some details from the model, can you
expand on your criticism and explain why the missing details would have
different impact on the result?

~~~
goodcodeguy
Based on this I am guessing they didn’t simulate the gravitational effect of
any surrounding bodies. If the asteroid core is the only object giving off a
gravitational force of course all of the fragments would reform around it.
This simulation just feels very incomplete and provides no real actionable
results.

~~~
gus_massa
My guess is that without rotation ... Why the model doesn't have rotation?????
It doesn't sound too complicated to simulate.

My guess is that without rotation, the tidal forces of the other bodies that
are far away are small enough to be ignored. In a perfectly even gravitational
field, all the parts of the comment has the same acceleration from the other
bodies and it can be canceled. (Like the "zero gravity" effect in the ISS.) So
only the forces between the fragments of the asteroid are relevant.

Anyway, the Shoemaker–Levy 9 comet suffered some disruption due to
gravitational tidal forces because it passed too close to Jupiter, and the
fragments formed a line instead of a ball.
[https://en.wikipedia.org/wiki/Comet_Shoemaker–Levy_9](https://en.wikipedia.org/wiki/Comet_Shoemaker–Levy_9)

------
lxmorj
Seems like two explosions would be much better. One to break up the rock, then
one to disperse the cloud as widely as possible. If you don't have the payload
to impart escape velocity onto the debris field with the second bomb, offset
both explosions such that the combined delta-v changes the path enough to
reduce or eliminate the likelihood of impact. We probably don't want
irradiated sand burning up in the atmosphere at scale...

~~~
gshubert17
Land a mass-driver on the asteroid. Escape velocity is small, perhaps a few
meters per second. Scoop up bits of rock, throw them away. Throwing them in a
consistent direction changes the orbit of the asteroid very slightly. With
enough lead time, throwing enough mass away may reduce the size of the
asteroid sufficiently or cause it to miss the earth.

~~~
lxmorj
Makes sense. I think this is a great way to slam Ceres into Mars and cut this
whole terraforming thing to the chase.

------
m4r35n357
Wow, who would have guessed it, Newton was right!

------
justizin
sounds like devops work.

