I suspect I am using a word casually, where you are using it technically. I don’t mean cohesive in the way that a drop of water on a table might demonstrate cohesion, so much as the simple idea of being closely related enough to be a single unit, rather than a bunch of “rocks.”
Either the pieces reach mutual escape velocity and disperse, or they don’t and coalesce. A few fragments might end up orbiting other fragments, but that’s about the only in-between case over any significant timescale.
The explosion of Alderaan (as depicted in Star Wars IV) appears to be a complete disruption, where every particle reaches a speed fast enough to disperse the planet for ever.
Of course there are lots of intermediate cases where only a fraction of the particles reach escape velocity; some of these would look nearly as impressive as the full dispersal case. The collision that created the Moon would have looked very impressive indeed, but even there most of the material eventually recollapsed into two separate bodies, the Earth and the Moon, so the energy of this collision does not appear to have exceeded the binding energy of the two planets.
Yes, it would. What remained of the Earth isn’t going to float up out of its own gravity well just because you removed the outer layer.
The Earth is already just “a bunch of rocks”.
Not sure if I’m running afoul of Poe’s law here, but this seems like the opposite of fighting ignorance.
First off, it seems demonstrably wrong. If the surface of the planet is ~70% water, then this planet is something more than a bunch of rocks.
More to the point, if I were to go into a thread and claim the Earth’s core were just a bunch of rocks I would be mercilessly drubbed as an ignorant fool.
The question I had was meaningfully answered, so maybe this was meant as a joke. But if I were to claim that the planet Earth and the Asteroid Belt are identical, I guarantee my ignorance would be commented on.
I’m going to weasel on the OP’s word “shatter”.
When you shatter a piece of glass, it breaks into a million tiny pieces. This effect is rather dramatic when you do it with a piece of tempered glass. A crack from the edge quickly becomes two cracks, then ten, then a thousand, and suddenly the pane looks like a giant spiderweb. But it doesn’t fly apart in different directions. Gravity might make it fall to the floor, but I’ve seen cases where the glass just sits there. Safety glass does this by design.
I am imagining a series of nuclear weapons place strategically across the planet, set to go off at the same microsecond, enough to produce an “Earth shattering KA BOOM”, pulverizing the surface of the planet, producing so much heat that everything melts a few seconds later and the atmosphere is vaporized.
According to Nathan Bergey, it would only take about 2 x 10^29 Joules to melt the surface of the Earth (70,000,000,000,000 10-megaton nuclear bombs), and I think my plan would require about the same energy. Yeah I know it’s not a full-on Alderaan, but the energy required is about 3 orders of magnitude lower.
So you only need 70 trillion nukes, instead of 70 quadrillion.
On second thought, that doesn’t help much. nevermind.
Not sure if I’m running afoul of Poe’s law here, but this seems like the opposite of fighting ignorance.
First off, it seems demonstrably wrong. If the surface of the planet is ~70% water, then this planet is something more than a bunch of rocks.
More to the point, if I were to go into a thread and claim the Earth’s core were just a bunch of rocks I would be mercilessly drubbed as an ignorant fool.
The question I had was meaningfully answered, so maybe this was meant as a joke. But if I were to claim that the planet Earth and the Asteroid Belt are identical, I guarantee my ignorance would be commented on.
Firstly about the water - that’s 70% of the surface. At most six or seven miles - and on average a lot less - out of a radius of four thousand miles is water. Taking the Earth as the size of a pool ball three inches in diameter, that’s an inch and a half radius, so the water to that scale amounts to, on a rough estimate, about a thousandth of an inch over not all the surface. In other words, dip your pool ball into a sinkful of water and the surface wetness is proportionate to the depths of the ocean. (And the surface roughness is appreciably higher than the planet’s, too.)
The Asteroid Belt is a bunch of rocks that are much too spread out to bind gravitationally to each other - and, if it comes to that, the Belt is empty space to a reasonable first approximate. A bunch of rocks equal in mass to the Belt and gathered within a few Earth radii of each other would soon make an Earthlike body… “soon” on the cosmic timescale, of course.
As to your ignorance, that’s not something anyone can or should comment on in this forum. 
Not to hijack my own thread, but I would like to use these two quotes to emphasize my point.
In AtomicDog’s case (apropos user name BTW) it seems to me that an intentional disregard of what was being said is the best explanation for that post. The concept of sustaining any nuclear reaction is meaningless.
AK84 states that the planet does not have enough Uranium to create a sufficient weapon, and I ask that we consider harnessing an asteroid from which to collect same.
Even mentioning the idea of critical mass dilutes the principal matters at hand, and perpetuates ignorance by implying otherwise.
And while I appreciate Malacandra’s post (another apropos screen name, IMO) I conspicuously specified in my post that I was referring to the Earth’s SURFACE.
There is some ignorance to be found in almost any non-trivial question; why else would someone ask a question, if not to learn something unknown? But there seems to be a sort of purposeful ignorance in too many of these answers.
To me, that serves to propagate ignorance, rather than to fight it.
I think the point that Chronos was trying to make, albeit somewhat elliptically, is that the Earth is not a solid object. It is a layer of relatively thin crust pieces floating on the mantle that insulates the nickel-iron core. (And although water covers about three fourths of the surface of the Earth, the amount of mass it provides compared to the total mass of the Earth is a small fraction of a percent.) So even “blowing up” the Earth such that the crust became deconsolidated would not result in the Earth disappearing; it would just reform and the surface would cool into a new crust.
It would take an impactor roughly the size of Mars, and moving much faster than the Earth’s orbital velocity around the Sun, to literally pulverize the Earth and disperse the remnants into widely separated orbits.
Stranger
I think the problem here is that we are all trying to answer the question as we understand it, although the question isn’t precisely defined. Just how thoroughly do you want to destroy the planet? Each definition of ‘destroy’ will require a different amount of energy, and therefore a different answer in terms of number of nuclear bombs. Do you want to remove just the top kilometer of the crust? That would destroy all complex life, but some bacteria might survive.
Do you want to remove the crust and mantle, but leave the core untouched? That would be a very comprehensive destruction of the planet, but it would require considerably less energy than dispersing the core as well so that every particle escaped.
The water on the surface of the Earth is such an insignificant fraction of the whole mass that we may as well ignore it, as Malacandra implied. And I suspect that AK84 may have mentioned critical mass in this context because it would be very difficult to get an asteroid’s worth of uranium together in one place without it spontaneously exploding, although that is just a guess on my part.
Yeah. For that matter, I doubt that Alderaan was completely gravitationally disrupted, for that matter. I’d bet that after a few years most of the mass of Alderaan was a molten sphere in precisely the place that the original Alderaan would have been - it’s just a lot easier to calculate the gravitational binding energy than the amount of energy required to prevent re-coalescence in a day, a year or a century.
Eh, there’s a pretty small window of energies where the planet would be blown to smithereens so thoroughly, while still remaining gravitationally bound. It’s much simpler to just assume that the Death Star provided sufficient excess energy that what it blows up, stays blown up.
Wow, guy, I was just making note that you can’t have an asteroid made of fissile material greater than its critical mass, which in the case of plutonium is less than twenty pounds. Am I wrong?
BTW, my name is because I’m a big George Clinton fan.
Correction, less than twenty four pounds.
You could have an asteroid containing a high concentration of fissionable material, but still sufficiently dispersed that it’s subcritical.
But it doesn’t matter, because there’s not enough fissionable material in the entire Solar System to destroy the Earth.
I’ll have to think about that - I hadn’t realized the difference was so small.
By the way, I did a bit more thinking about the gravitational binding energy. If we continue to assume a constant density (which seems to produce accurate enough results for the Earth), then the equation for gravitational binding energy can be reduced to Gravitational constant times density squared times radius to the fifth power times a constant that amounts to 10.5 or so. This tells us that most the binding energy is in liberating the big pieces - giving breaking the Earth into a hundred smaller pieces and making them gravitationally unbound from each other uses almost the same amount of energy as complete gravitational disruption. This formula is also a reminder that the gravitational binding energy of everyday objects is tiny. For an ice cube, or a house, or even a mountain, the gravitational binding energy is going to be smaller than the energy due to the chemical/mechanical/frictional forces that hold it together.
Why fight gravity? Instead, join it. Destroy the planet by creating a small black hole, which would consume the planet, and then decay and spew the matter back out. I’m guessing now, but presumably it would create a new planet in the same orbit from the same mass, which some might call the same planet but it would definitely involve the destruction of the current one.
I have no idea what the timeframe would be for the black hole decay due to Hawking radiation, it might happen after the Sun goes flooey.
Is there enough Deuterium?