We need to be worrying more about smaller ones than we have been:

Simulations show that the material of an incoming asteroid is compressed by the increasing resistance of Earth’s atmosphere. As it penetrates deeper, the more and more resistant atmospheric wall causes it to explode as an airburst that precipitates the downward flow of heated gas.

Because of the additional energy transported toward the surface by the fireball, what scientists had thought to be an explosion between 10 and 20 megatons was more likely only three to five megatons. The physical size of the asteroid, says Boslough, depends upon its speed and whether it is porous or nonporous, icy or waterless, and other material characteristics.

“Any strategy for defense or deflection should take into consideration this revised understanding of the mechanism of explosion,” says Boslough.

We really need to become much more spacefaring to be in a position to do anything about this, and ESAS doesn't cut it.

Considering that -- all other things being equal -- the energy of explosion will scale directly with the mass of the impactor, and that asteroid sizes follow a power law such that there are 200 times as many for each reduction in diameter by a factor of ten, then going from 15 megatons to 4 megatons means (if I'm doing this right) nearly a threefold increase in impact frequency. Not a good thing in a world of 6+ billion people and lots of nuclear warheads in launch-on-warning status.

What are the respective odds of detecting asteroids of varying sizes before they hit the Earth? While any asteroid impact would be bad, surely it would be less bad if everyone knew it wasn't a bomb explosion.

Jay: more than a factor of 4 increase, I think.

Lots of speculation on my part in this comment and I haven't watched the movies so I apologize if I've missed out on some details like where, if anywhere, in relation to the following the example of a "62 thousand ton stationary asteroid" fits in.

From Wikipedia:
"Different studies yielded varying estimates for the meteor's size,[1] including 50 meters,[2] 60 meters,[3] 90 to 190 meters,[4] and up to 1200 meters in diameter.[5]"

Since the Sandia article talks about "only a fraction as large as previously published estimates", "much smaller", "a far smaller asteroid" and so on what does that leave us with? Something as small as 5 meters in diameter when engineered to soak as much energy as possible?

I'm a bit surprised the article/information was released but now that it's out there if the Pentagon & co haven't already worked through the possibilities (or thoroughly discredited them) they might want to get busy. Even if completely discredited for now I'm guessing they've got something new to continuously check for in future advances of materials science.

One new possibility, let's call them "soak bombs", might make nukes obsolete as far as non-MAD physical destruction goes (MAD, N-bombs and EMP applications remains the domain of nukes) if the mass to yield ratio can be brought far enough down. Might seem counter-intuitive but while nukes are extremely effective in terms of pure energy most of that energy isn't directed towards the target even with ground or low-altitude bursts (and with ground bursts being far less effective than low-altitude bursts). However a soak bomb could deliver a much higher percentage of its total energy to the target which should make up for much of the difference since one can only obliterate the target so many times... In addition that makes soak bombs more precise than nukes although that goes for just about anything ^_^

Maybe soak bomb technology in the form of a sort of shaped charge (one directing as little energy as possible backwards along a tiny area centered at the trajectory) could be combined with the "Rods from God" concept in a non-destructive supporting role (small soak bomb yields not reaching the ground) clearing the way through the atmosphere for --and thus increasing the speed and yield of-- the rods.

Since a soak bomb won't result in radioactive fallout etc. maybe small low-yield versions could be used in sort of an "airspace carpet-bombing" capacity while leaving ground structures mostly or completely unaffected.

Apologies offered if this was all completely idiotic ^_^;

Anyway good Yule and/or merry Christmas everybody!