cool...Actually, despite the impression given by a couple of movies from years past, neither a tactical nuke, nor even a strategic H-bomb, would be able to "vaporize" a comet of this size, nor even put a serious dent in it.
Our nuclear weapons are powerful enough to do enormous damage to things on the human-sized scale, but we tend to forget how small that can be compared to many of the objects found in nature.
The largest thermonuclear weapon in our arsenal has a yield of about 50 megatons. That's 2.1 x 1017 Joules of energy. Using the best-case scenario (the comet is composed of nothing but ice -- no rock or metal -- and is no colder than the freezing point of water, and the nuke imparts all of its energy into the comet instead of radiating much of it into the surrounding space), and using the fact that it takes about 3014 Joules of energy to vaporize one gram of 32-degree(F) ice, we find that a 50-megaton nuclear weapon can vaporize no more than 2.1 x 1017 / 3014 = 7.0 x 1013 grams of the comet, which would make for a hemi-spherical crater of (2 x 7.0 x 1013)(1/3)/(4/3) * 2 = 77,887 cm in diameter, or 77887 / 2.54 / 12 = 2,555 feet across. Call it half a mile. And if there's any rock or metal material in the asteroid instead of just pure ice, the volume of the crater vaporized will be considerably smaller than that.
Compare that to the description of the size of the comet in the article: "Manhattan-sized space rock". This is rather imprecise, especially since Manhattan is extremely oblong (13 miles long by 2 miles wide), and comets tend to be pretty spherical, but let's conservatively say that this means the comet is a sphere five miles in diameter. A half-mile crater would be a minor blemish on its surface, and would come nowhere near vaporizing the whole comet -- the amount of (ice) material vaporized would only be 0.08% of the comet's total mass, or 1/1240th of it. You'd need more than another *thousand* 50-megaton strategic nukes to actually vaporize the comet -- again, if it's made of pure ice. Any rocky material would vastly increase the number of nukes required -- rock is a hell of a lot harder to vaporize than ice. And it would just laugh off a *tactical* nuke.
Remember the movie "Armageddon", where they split an asteroid "the size of Texas" in half with one nuke? Ain't gonna happen... That amount of energy, even if it *could* actually split the thing, wouldn't even be enough push the two halves apart against their own mutual gravitational attraction.
Similar calculations reveal just how freaking hard it would be to even deflect something of this size, unless you started *years* in advance of the expected impact.
Many people underestimate kinetic energy as an effective tool. If this comet were slammed with another comet of equal size going the opposite way at, say, 130,000 mph, there wouldn't be much left of either. Mostly just an ionized patch of gas, glowing at first and gradually fading out. It would probably create other problems in the solar system, especially with scientifc satellites and maybe Loral and other commsats.
cool...So what you're saying is that there isn't a Snowball's chance in Hell. Copy that.
The movies frequently do not bear any real resemblances to real life. You have made some good points. So how far out would we need to start in order to deflect a comet of the size that we are talking about?
I'd like to add that we probably do not have enough suitable nuclear weapons to use on a comet and our choice of delivery vehicles are limited.