The object isn’t traveling “absent influence from some other mass”; it’s under the gravitational influence of the sun. The cloud won’t "expand forever’; the impetus will simply alter the characteristics of the elliptical orbit, which will very likely reintersect Earth’s orbit, and with precession will eventually come around close to the Earth. The amount of delta-v to effect escape from the Solar system at Earth’s orbit is ~42km/s. An average acceleration of 100G would have to be applied for 43 seconds to attain that additional velocity, whereas the actual pressure wave from a nuclear detonation that occurs in atmosphere would travel by in a few seconds and apply nowhere near this acceleration at its peak.
It would be extremely unlikely to encounter a large solid extrasolar object as large masses tend to coalesce around stars, and if we did, it is very likely that we’d never see it until it was far too late, as it would be moving at extreme speeds (somewhere on the order of the >200 km/s relative speed of the Solar system with respect to the galactic hub) and coming from any possible direction. Long period objects are statistically far less likely to pose a threat than identified near Earth objects simply by virtue that there is a much lower frequency of incidence that they could even intercept the Earth, and their period is probably not strongly (or at all) coupled to the Earth.
Nowhere in this has any valid argument been made for why it is better to attempt to fragment a PHO rather than just push it whole (or at least as whole as it already is) into a stable, identified orbit that will not intersect with the Earth for the calculable future. Fragmenting such an object will not pulverize it or make it disappear, and breaking a large object into smaller chunks does little to reduce the hazard, and indeed, spreads out the footprint of damage further.
Wouldn’t you rather have that footprint spread out over centuries and in manageable chunks than all at once? And some of it burning up harmlessly in the atmosphere? And some of it never reaching Earth at all?
I’m not saying that fragmenting is the best option, but it might be one to consider.
Newton might disagree with you. Will you at least agree that absent any other nearby mass, it will? The Sun doesn’t stop actions, it only influences them.
Perhaps not (but what speed will?), but the new vector will accumulate deviation over time, and a few thousand years from impact, it will be in a totally different path and orbit.
Look, if you’re just looking for someone to say “Damn yes! At some point with a unbelievably big bomb we can blow stuff up and be safe” Then sure, I agree. In the meantime, less dramatic coursse of action are better avenues to pursue.
To elaborate on that: In space, everything travels in an orbit. If we approximate space as a vacuum and gravity as Newtonian, then a bound orbit will be a closed ellipse (Stranger already covered why unbound orbits are unlikely to be an issue). If you make a small change to an object’s velocity, then it’ll end up in a slightly different ellipse than it was before, but once in that new orbit, it’ll stay in that new orbit indefinitely. And if the old orbit came uncomfortably close to intersecting the Earth’s orbit, then the new orbit (which is only slightly different from the old one) will also come uncomfortably close.
Look, I don’t care about all the scatter vs. slug-type impact. If there is an asteroid aimed at me, I want to nuke it. Kill the bastard! What’s it going to do? Kill me deader? FIRE!!!
Yes, I read that. It makes sense and sounds like a good idea. But right now it is just an idea. Just like the gravity tug idea that has a formal paper written.
One of my buddies is an astronomer working for NASA studying asteroids, now also looking at the manned mission to an asteroid. He is intimately involved in this. He tells me we need more information, and that it is still an open question.
Musicat said:
Consider the Comet Shoemaker-Levy impact on Jupiter. It broke up into what, 11 pieces? Then had a string of impacts. Now those impacts didn’t do much to Jupiter, and the comet as a whole wouldn’t have done much to Jupiter. On the other hand any one of those pieces hitting Earth would have been a bad day. Does it really matter if you get one solid chunk or a string of slightly smaller impacts that still devestate the planet?
Consider this: when calculating the possibility of impact, we’re not talking absolutes, were talking windows of the path and probabilty of impact given size and window of path. The further out in time, the wider the window of probability is. Far enough out to do something is far enough out that we don’t know if the item will hit or just be a near miss. Maybe that window is somewhere between the Earth and Moon. Maybe that window covers both the Earth and the Moon and the space between.
You are proposing making a single object that can be tracked and possibly deflected and instead breaking it up into a cloud of objects that will still essentially pass through that same intersection window. You are turning a possible big hit into a likely somewhat smaller hit or series of hits. Plus very likely scouring Earth’s orbits of satellites. Making objects harder to track and at the same time us less certain of their paths.
The alternative is the “last minute play”, which is that we see it coming in that year. We have a few months to launch something and intersect, but no real time for deflection to do much good. Again, do we take our chances that the projected path crossing will be a near miss, or ensure a hit by blowing it to smaller pieces and hope the pieces are small enough and spread enough that we only get part of the strike? What if we can’t pulverize the asteroid, and only turn 1 planet killer into a million city killers?
Sorry, that was unduly snippy. My frustration is in no small part my own inability to explain this scenario clearly without a whiteboard to draw diagrams and work through a few sample calculations in detail.
As Chronos notes, things that are in orbit will remain in orbit unless you achieve escape velocity, which is unlikely for an object moving at around Earth’s orbital speed subject to an impulse of at most a few seconds, as the magnitude of the impulse would have to be huge to provide the needed acceleration. The sort of impulse a single explosion would provide (which is probably on the order of a few hundred m/s at a maximum) would merely adjust the eccentricity of the elliptical orbit slightly, and the object would return to the same point at nearly the same orbital period, not accounting for orbital precession and gravitational perturbation. A spread of objects with various impulses issuing from the same initial orbital condition will periodically return through a region about that same point.
To address the question, “Wouldn’t you rather have that footprint spread out over centuries and in manageable chunks than all at once?” the answer is absolutely not! I’d rather deal with one large object on a known trajectory that is more visible than hundreds or thousand of still-large-enough-to-be-catastrophically-hazardous objects that are harder to identify and moving in a spread of orbits that will periodically threaten to intercept the Earth turns one bad day into a horrible bunch of years.
By analogy to ICBMs, fragmenting a large object is like taking one large warhead and turning it into a bunch of somewhat smaller ones, which is exactly what the United States and USSR did in response to the concern about disabling counterstrike and anti-ballistic missile defense. By deploying multiple independently-targeted reentry vehicles (MIRV) you spread out the destructiveness and make it more difficult (literally, by an order of magnitude, as most MIRV systems carry ten or more RVs) to intercept.
I’ll take that. Cities can be rebuilt; a planet-killer means extinction. Faced with extinction, I’d gladly accept the alternative of the loss of every single city on Earth.
A “million city killers” might still effectively be a planet (or at least human) killer. If a large NEO was fragmented, the smaller fragments will airburst instead of reaching the ground. It’s not clear if this is preferable, the total energy release is the same.
Multiple airbursts spread out over a large area would kill a very large number of people in a short period of time. Basically, you’re talking about blasting and burning an entire hemisphere of the Earth. One large impact would kill less people immediately, but the secondary effects might be more serious and long term. For example, the Chicxulub impact caused a huge release of carbon dioxide and sulfates as bedrock was vaporised, affecting climate and causing acid rain.
Both scenarios are apocalyptic. The dust and smoke thrown up into the atmosphere would block out the sun and interrupt photosynthesis.
Fragmenting a tunguska-sized (city killer) impactor might be somewhat viable if one was detected too late to deflect it. Spreading out the impact over a larger area should lead to smaller effects at ground level.
Shoemaker-Levy wasn’t fragmented by a bomb, but broke apart due to gradually weakening internal forces. And look how much it spread apart the first chunk from the last, albeit in the same direction, and the time from fragmentation was short (I’m not sure, but was it months to years?). Huge difference from the nuke-it idea with more time.
Planet killer is a misnomer, it’s shorthand for an extinction-level impact. The point is, faced with such a large impactor breaking it into fragments may not actually help.
Any chance of using a slower means of propulsion to change the course of the offending object? Could an atomic pile produce enough heat to vaporize the material and produce thrust for deflection. I suppose this could be difficult for a spinning object, but assuming a stable orientation, is there enough energy density in anything we could practically install for this purpose? It might make sense to try this while the problem is still about diverting one object, instead of a gazillion smithereens.
Would a laser vaporizing one spot on the object, which outgasses and produces thrust, be enough to deflect such an object if detected far enough in advance? That would solve the issue of placing a rocket on the surface, and so on. But would the gas/dust cloud ejected serve to block the laser beam? Could the beam be moved to new target points (to avoid the debris cloud) or would that dilute the thrust vector too much?