Asteroid 99942 Apophis impacting the Earth in 2029

[Glenstr]

The simple answer is no. Some would miss, the majority would not.

I guess that would depend on a lot of factors, the size & number of fragments in the rubble pile, or the number & size of fragments created from blowing up a solid object being a couple.

If I drop a 10' rock of a 1000' cliff it's going to hit one 10' diameter spot. If I set off a large charge in that same rock before it's 1/2 way down then few, if any fragments are going to hit that same 10' area it would have hit if it was intact - and consider that the exploded fragments trajectories are dealing with Earth's gravity.

If I drop a big bag of gravel off with a charge going off in its center the effect will be the same, only trajectory changes in the already loose fragments are going to be much greater than the first example. In fact, few would even hit within a 500' circle around the original point of impact.

Now do this to a pile of rubble a few million km's from us in the vacuum of space, where the altered trajectories won't be affected by Earth's gravity..

 

[Ophiolite]

You need to compare the velocity of the bolide, which is relatively very large, to the relatively small velocity change imparted by the explosion. In your example the explosion is orders of magnitude greater than what we could practically deliver to an incoming asteroid. I'm sure there is published research out there on this - time permitting I'll track something down and post a link.

 

[D H]

The shock wave generated by a nuclear detonation is responsible for most of its destructive force. On earth, superheated air provides the medium to convey blast energy. In the vacuum of space, you need another medium. The mass of the nuke would provide relatively few, but, hugely energetic particles. Peppering an asteroid in this manner is not an efficient way to move it. You need to hijack some of the asteroid mass to provide a huge number of lower energy particles to convey the force: much like a lower velocity explosive on Earth is a more efficient way to dislodge a stump.

This is completely wrong. There have been a number recent posts that carry the same misunderstanding.

There is no shock wave in space. I previously explained how nuclear detonation changes the trajectory of an asteroid or comet, so quoting myself,

The way nukes work to divert an impact by an asteroid or comet is simple. Nuclear explosions generate a lot of high frequency radiation (X-rays and gamma rays) and neutrons, preferably a lot of neutrons. A thin layer of the asteroid/comet absorbs this bath of incoming neutrons and high frequency EM radiation. The radiated material then evaporates, making for the equivalent of a rocket. Neutrons are best because they penetrate deeper than does the high frequency EM radiation. Ideally, a nuclear explosion will result in a few percent of the material of the asteroids/comets material vaporizing.

To elaborate on the above, because neutrons penetrate deeper than does EM radiation, it's the neutrons generated by a nuclear explosion that are most effective at diverting the object. This means that a fusion bomb would be more effective than a fission bomb because ounce for ounce, fusion produce a lot more neutrons than does fission.

 

[Chronos]

Marshall Eubanks, a physicist educated at MIT and former member of the Technical Staff at the Jet Propulsion Laboratory, had this to say at http://www.researchgate.net/post/What_would_be_the_effect_of_a_nuclear_explosion_in_space :

"[a nuclear] bomb might ablate a 10 meter layer from the entire bomb-facing side of the asteroid and send this material off at 10 km / sec, causing a 10 meter / second impulse to the rest of the body."

The National Research Council report "Near-Earth Object Surveys and Hazard Mitigation Strategies(2010) notes at
http://www.nap.edu/openbook.php?record_id=12842&page=78

"... [Dr. David S.P. Dearborn, Lawrence Livermore Labs] simulated the effect of a nuclear standoff detonation on homogeneous 1-kilometer-diameter NEOs with densities between 1.91 and 1.31 g/cm3. In these numerical models of a standoff burst about 150 meters above the NEO’s surface, about 40 seconds after the burst the NEO’s speed change ranged from 2.2 to 2.4 cm/s. Approximately 97.5 percent of each NEO remained intact (the NEO was held together by gravity only—it had no tensile strength), while about 2.5 percent of its mass was ejected at greater than escape speed by the rebound to the shock wave that passed through the body in reaction to the ejection of heated material."

Are these references sufficient to justify the inference that momentum is conveyed by material ablated from an asteroid in a nuclear detonation?

 

[mfb]

You need to compare the velocity of the bolide, which is relatively very large, to the relatively small velocity change imparted by the explosion. In your example the explosion is orders of magnitude greater than what we could practically deliver to an incoming asteroid. I'm sure there is published research out there on this - time permitting I'll track something down and post a link.

You also have to take into account the distance to earth, which is very large in realistic scenarios, with the size of earth.

If the fragements move away at a typical velocity of 1m/s (the escape velocity of an asteroid that would be a global threat), after one year their path changed by ~30000km* - enough to miss Earth with typical velocities. A few would happen to move in the direction where they still hit earth, but most would not.
Early warning is key. If you have ten years of warning time, a velocity change if 10cm/s (for the whole object or for fragments) is sufficient.

*not including the nongravitational effects that can alter the orbit differently for smaller objects

 

[GiantSheeps]

Couldn't we use a method like the one in this video http://www.nasa.gov/content/what-is-nasa-s-asteroid-redirect-mission/ ? Basically send a probe out there, wrap it in a bag, and bring it somewhere else? (I know Apophis is no longer a threat, but for other, future asteroids)

 

[Vanadium 50]

Basically send a probe out there, wrap it in a bag, and bring it somewhere else

Why not try it on Earth first. That should be easier. Use, say, the Rock of Gibraltar. Wrap it in a bag and move it to, say, the South Pole.

 

[GiantSheeps]

Why not try it on Earth first. That should be easier. Use, say, the Rock of Gibraltar. Wrap it in a bag and move it to, say, the South Pole.

Okay I was making a joke, but if you watch the video that NASA put out you'll see what I mean, I put a link to it in my post