Would the equipment we use now to watch for ELE asteroids have picked up the K-T asteroid? If humans had been on the ground at the time, when would they have been able to see it with their own eyes? Hours before impact? Minutes? Seconds?
The answer is a qualified maybe. The asteroid that preceded and presumably caused the Cretaceous–Paleogene (K-Pg) extinction event was very large, on the order of 10 km in width. Since the mod-‘Nineties, starting with Spacewatch astronomers have been surveying the skies for Near Earth Objects that could pose a future hazard. Assuming a power law distribution of object sizes holds (and it appears to from observations of the asteroid belt and impact craters on the Moon) they’ve found the vast majority of objects >1 km that are likely to cross Earth orbit at some point, and discovery of new objects has trailed off as most objects are cataloged. There remains, however, the potential for very long period comets or large extrasolar bodies which we have limited or no information about and might only have a few months warning. Even if we did spot such objects there is no practical sceme for deflecting such large objects and no way to protect human civilization from the effects of such an event.
Stranger
Approximately 90% of the 1km+ asteroids have been found. This is based on a statistical argument. (that if you sample a random section of the sky and more than 90% of the asteroids you see in the part of the sky you’ve already found, then you probably have found about 90% of them)
So we’d probably see the asteroid months beforehand.
As for if humans were watching for it- during the night an object like that would be visible if you were looking in the right place. It would grow increasingly brighter over time. During the minutes before impact, that wouldn’t take very long - you’re talking an impact at 7+ kilometers per second. The actual rock is so fast all you’d see is a trail blurring to the surface.
I would hope that if we knew it was coming we’d try a parallel, herculean effort similar to the Manhattan project. Not just 1 main effort but several. We are a very rich civilization. There’s at least a chance we’d be able to nudge it off course by setting off dozens of nukes on one side.
Each one would be a nuclear shaped charge, they’d fire gas at high velocity into the side of the object, imparting a velocity change to it. The weapon itself wouldn’t actually try to “blow up” the asteroid or anything silly like that. No drilling either.
The katey asteroid was estimated to be traveling at 20 kilometers per second. As SoaT mentioned, it was somewhere around 10 kilometers in diameter. So let’s pick round number times–10 hours, 10 minutes, 10 seconds (and ignore complicating issues such as the angle it arrived from.) At 10 hours, it would be 720,000 km away and cover around 0.047 minutes of arc, or roughly 1/10th the diameter of Mars viewed from Earth. At 10 minutes, it would be 12,000 km away and cover 2.86 minutes of arc, or roughly 1/10th the diameter of the moon viewed from Earth. At 10 seconds, it would be 200 km away and cover 172 minutes of arc, or close to 6 times the diameter of the moon viewed from. The brightness depends on the reflectivity of the asteroid and the angle to the sun (are we seeing a “full asteroid”, “first quarter asteroid”, “new asteroid” etc.)
But we still could round up a bunch of old actors and send them hurtling into an almost certain death, couldn’t we? If I and my world is going to perish in a horrific interstellar holocaust, it would still give me some small comfort to know I’d ticked that off my bucket list.
That would be a very difficult weapon to design (Shaped nuclear charge) and you may be overstating the effectiveness of a nuclear explosion on a very large asteroid ( > 10 km diameter)
Even an all out effort would take longer than expected.
As it happens, I’ve worked on a study of this very issue, and proposed a concept for redirecting objects of moderate size (~1 km diameter iron-nickel bolide). In [POST=12775897]this post[/POST] I addressed the feasibility of shifting the trajectory of an incoming hazardous object. Redirecting an object of such size is at least remotely feasible, provided you can deliver several dozen devices to intercept with the object, which is more of a logistical challenge than a technical one. Redirecting a much larger object, however, becomes a substantial challenge not only because of the additional mass but because the impulse will impinge upon only by a fraction of aspect of the body and would likely be absorbed as deformation within the body (inelastic transfer or liquification) rather than uniformly delivered to the entire aspect. Moving really large masses requires some fundamentally different method of propulsion than just pushing because at those scales a “solid” body doesn’t act very solid.
Stranger
Not to mention how many asteroids are rubble piles. Turn a bullet into a shotgun blast, you aren’t really helping.
Really? Because shotgun blasts have much lower penetration. It’s the difference between being slapped and being punched - the smaller the surface area, the more energy is focused at the point of impact.
More like the difference between someone dropping a 10,000 pound rock on your head from a mile up and someone dropping 1,000 10 pound rocks on 1,000 people’s heads from a mile up. The huge rock is enough overkill that if you break it up and spread it about, there is plenty of kill left in each of the fragments to take out even more people. With the asteroid, instead of just super-duper killing one major city, you could just plain kill dozens.
If the asteroid is on an impact path, all of its kinetic energy is getting absorbed one way or another. With an object on the scale of the K-T asteroid the magnitude of the energy is such that it doesn’t make much difference whether a bit more of it is absorbed in the form of atmospheric heating vs melting the crust on impact. Either way, the entire globe is in for a really bad day.
A nuclear warhead detonated in the vacuum of space produces no fireball and no blast. It is simply an intense pulse of X and neutron radiation. A precision stand-off detonation would just vaporize a thin layer of the asteroid’s surface material – whether that was a monolithic object or a gravel pile – creating an ablative impulse and associated delta-V in the opposite direction.
Re time to implement, there are plenty of ready launch vehicles for this – they’re called ICBMs. A Titan II ICBM launched the Clementine probe to the moon, so it’s a matter of reducing the payload for increased delta-V. However the guidance system would have to be replaced, as it’s not designed for extended deep space use, and a terminal homing and fusing system would have to be devised.
I don’t know how long that would take, but the basic technology already exists in ABMs: Exoatmospheric Kill Vehicle - Wikipedia. By coincidence the last of 528 nuclear detonations within earth’s atmosphere was a Nike Hercules anti-ballistic missile interceptor in 1962, Operation Dominic Tightrope: Operation Dominic Tightrope | This Day in Aviation
See “Deflecting Asteroids by Means of Standoff Nuclear Explosions”: http://research.dynamicpatterns.com/wp-content/uploads/2011/03/Deflecting-Asteroids-by-Means-of-Standoff-Nuclear-Explosions.pdf
“Nuclear Explosion Near Surface of Asteroids and Comets - General Description of the Phenomenon”: http://csc.ac.ru/news/1997_1/ae27.pdf
C’mon, Stranger – the Mods were in the 1960’s, not the 90’s. 
Fascinating topics and perfect for this topic. 
However, the nuclear weapons described are NOT a shaped directional charge and the maximum size to be effective is closer to 1100m in diameter, not the 10 km of the K-T asteroid . Although still sufficient for this task for anything not discovered yet!! as the really big asteroids are all charted fairly well
I still love this link for showing just how many there are
Depending on the size and timing, and on the composition of the object, it might be better not to use your nuclear power in a big dramatic blast, but to instead do something more gradual. If you’ve got an icy object, you might want to burrow a reactor into it, to heat portions of the object’s material into steam, released in a jet.
Maybe so. It seems like a series of small nukes would accomplish the same thing. Either by ablating layers off the asteroid with each flash or by impinging hot gas onto the side of it to push it in the direction you want. You could use spacecraft that are Apollo lander size, loaded with dozens of nukes each, that deliver this continuous series of detonations.
I don’t understand why stranger claims that the asteroid being “springy” makes any difference. If the asteroid gives off a jet of gas or absorbs a jet of high velocity gas from the nuke, either way, the total momentum of the asteroid has been changed. Internal forces don’t matter. Doesn’t matter if the asteroid is spinning, either. It just matters where you set the nuke off.
But yeah, even pushed to the absolute limit, with all the countries of the world building rockets in parallel, with emergency commandeering and building new plants, with round the clock shifts to build optimized devices to do this, it does sound like it would take on the order of 2-3 years. (numbers based on ww2 performance)
I get that anyone within a few thousand miles of the point of impact would be toast either way. That goes without saying. It’s just that I was under the impression that another aspect of a dinosaur-killer’s impact would be the nuclear winter caused by the billions of tons of water and/or dirt blown into the atmosphere by its impact. If most of it is burned up in the atmosphere, would that still happen? Or is that basically irrelevant?
The erstwhile bullet, now shotgun blast
- Is composed of several smaller objects.
- Many of which will now be on a “miss earth trajectory”
- Others will be burnt up by our planetary protection system, i.e the atmosphere
- As for the rest, well it’s not like we are going to fire just the one, or a single salvo. It’ll be more like “ok now they are 25, pieces, 6 of which look dangerous, launch on them”.
The atmosphere is not a “planetary protection system”; it is a critical part of our biosphere that performs a variety of functions needed for life to exist, including selective filtering of sunlight, moderating the day/night temperature cycle, the transport medium for the hydrological cycle, providing wind for dispersing pollen, and of course, we and other animals use it as a readily available oxidizer for respiration. Meteors much larger than ~20 meters in width will not “burn up” in the atmosphere and will result in ground impact which can throw millions of tons of debris into the stratosphere; even those that do deconsolidate can release enormous destructive impulse through rapid atmospheric heating that could destroy structures and kill people if it occurs over a dense urban or suburban area.
It would be far better to push a hazardous object aside into an orbit that will not intersect the Earth rather than to break it into smaller and more difficult to track components which may pose an indefinite hazard. Unfortunately, as Darren Garrison, many asteroids are loose aggregations of material that will not remain intact with any lateral impulse, and so in order to deflect the entire mass some way has to be found to either secure the mass together or give a distributed push that shoves all parts equally. Just blasting away at an object in the hope that it will deconsolidate into small components not large enough to be a hazard (especially if they will still collectively impact the Earth) is not a good plan.
Stranger