My husband and I were talking about the difference in the composition of comets and asteroids when he posed a very interesting question: would a giant asteriod made of cotton do the same kind of damage as one made of rock? Could a cotton ball “the size of Texas” destroy all life on Earth if it struck us?
(Yes, I know it would burn up in the atmosphere. Let’s pretend it’s made of a magically un-burnable material.)
My stance was that the damage caused by an asteroid impact is not necessarily because of what the asteriod is comprised-- it’s the speed and force of the impact. The shock wave travelling in front of the astroid alone would do a lot of damage.
I tried to study this in more detail, and found a lot of scientific formulas, such as this one:
So, from this I gather that the kinetic energy of a comet (comprised of ice rather than rock) is less, but is it enough of a difference to “save” the Earth?
A giant cotton ball will have a lot of air in it. This greatly reduces it’s density. So when you are talking about a limited size (the size of Texas), it will have a much smaller amount of mass than a rock or ice. We would all probably die anyway, but the impact would not be as cool as a Texas-sized rock or ice cube.
Also, you can’t specify it’s a magical nonburning cotton. If you want it to be a factual answer, you have to allow it to be normal cotton. Maybe magic cotton bounces off of everything and will do no damage at all…
Even some of the rock and ice burn up in the atmosphere, so cotton will have to as well.
Maybe change the question to, “What if a ridiculously large amount of cotton hit the atmosphere, such that after burning in orbit, a Texas-sized chunk was still left and still burning when it impacts the surface of the Earth?”
I don’t see why not. The real question is the mass (or, rather, the momentum) and how it disperses as it passes through the atmosphere. This is the big problem with a lot of asteroid-style disaster movies: just because you break it into two pieces doesn’t mean anything; there’s still the same amount of momentum coming in.
Basically, if you had a giant hunk of material the density of cotton and which would burn up (disperse) at all as it came through the atmosphere, it would have the same momentum as a smaller chunk of rock with the same mass. When it hit, it would cause a similarly-sized impact.
But the impact would be over a far greater area, wouldn’t that significantly diffuse the damage. Also would the atmosphere have a much greater effect on the cottonball causing much more air resistance than to a rock.
I believe the massive damage from a meteor is due to shock waves going through the earth, and also dust particles sent into the air. I susspect the cottonball would mostly burn up in the air, leading to perhapse more dust particles (of carbon soot in this case) but very little shock wave damage.
You’re assuming that the density of a huge “Texas sized” ball of cotton is going to have the same overall density and fluffiness as a regular little cotton ball. I think what you would be dealing with under the effects of the Earth’s gravity, is an object that is more akin to a massively compressed piece of felt. Also, for an object that size it is unlikely that the trip through the atmosphere is going to burn up a substantial part of it.
How much does the compressability of the cottonball matter at what I imagine must be planetary velocities? A 1kg rock moving 10m/s is going to hurt a lot more than a 1kg cotton ball moving at the same velocity, because they dissipate their kinetic energy differently. Perhaps at the hundreds-to-thousands of km/s the cottonball would be moving, it would still pack quite a wallop, but again, this Texas-sized ball is going to squish quite a bit when it hits the Earth’s surface, rather than dissipating all of it’s energy in a fraction of a second. I would imagine that would generate tons of heat, and if we must deal with an inflammable cotton-ball, I suppose it must simply vaporize, releasing much of that heat into the atomosphere, rather than gouging out quite the massive crater a rock of similar mass would excavate. But this heat dissapation could be quite lethal to all life if it could raise the temperature of the atomosphere enough to cause widespread death and combustion from exposure to super-heated air.
Drop a bale of cotton on yourself and see how fluffy it is. A Texas-size fluffy cotton ball will compress to an even higher density under earth’s gravity.
If the thing is falling toward Earth, then our gravity won’t compress it at all until it lands - impact with the atmosphere would flatten it, maybe its own gravity would compress it some too, but I don’t quite get how you think Earth’s gravity would deform it.
Yeah, the thing is in a straight-trajectory free-fall until it hits the Earth, so Earth’s gravity doesn’t apply to its shape of degree of deformation until it impacts. Considering that when the leading edge of the cottonball hits the Earth’s surface, it’s trailing edge will be about a thousand km in space, I don’t the atomosphere much matters either.
However, a Texas-sized cottonball (meaning, I assume, a sphere of cotton with a diameter the breadth of Texas) will have some gravity of its own, now that y’all mention bodies attracting bodies. I have no idea what the density of a fluffy ball of cotton is, but a sphere of that size must still have considerable mass, and so cotton on the surface of that sphere will have perhaps non-trivial weight when you consider the force needed to compress fluffy cotton. The Texas-sized sphere is going to collapse to some degree under its own weight, and thus be quite a bit more dense than the cottonballs you pick up at the drug store to scrub your zits. This density is highly relevant to the question of how the cottonball will dissipate its energy on impact. I assumed fluffyness, but perhaps that was a bad assumption. I just don’t know enough about the properties of cotton to predict how a hunk of it that size will compress under its own gravity, and hence how an object of that final density will behave.
The vast majority of space junk reaching Earth never touches the ground – the shock and destruction are caused by the energy dispersed in the atmosphere over a very short time. A giant cotton ball, burning or not, might not be able to deliver its energy that efficiently.
I should have said the Earth’s gravity will not affect the falling cottonball very much, and certainly won’t compress it. For an object that size, tidal forces will stretch it to some degree, though, given the shallowness of Earth’s gravity well, not all that much. If the cottonball were falling into a smallish black hole, you’d see some nice cotton spaghetti.
what you’re really talking about when you say “force of impact” is impulse. Impulse is a force applied over a time (impulse=F*t). however, impulse is also equal to the change in momentum of an object (in this case the object is going from moving towards the earth to a relative velocity of zero). impulse describes why we land a jump easier when we bend our legs. the bend of legs increases our time in motion, impulse is constant because the change in momentum doesn’t change with time (velocity still goes to zero). so if t increases but impulse remains the same, F must therefore decrease. so the real question is if a giant cotton asteroid takes a longer time to stop moving that a rock asteroid. logic would seem to say yes, being that the cottonball can compress and increase it’s stopping time. however, if both rock and asteroid are smashed to bits upon collision, the times could relatively comparable. i think the only logical answer is to launch a giant cottonball at a nearby useless planet and gain sound experimental data.
I used to work cotton as a teenager. A bale weighs about 500 lbs. A Texas size cotton ball would make a hell of a bale once it hits the ground and gets compressed. Sure, not as dense as rock, but we would still be hurtin’.
I remember how difficult it was to unload the cotton from the picker if the cotton had any kind of moisture in it. It was really heavy. I wonder if this magic giant cotton ball would pick up any moisture as it made it’s way through the atmosphere?