this post was submitted on 02 Dec 2024
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I'm not so sure... At those speeds, it would've taken under 10 seconds to completely clear the atmosphere. Even with intense compressional heating, I don't think it would've been in contact with the atmosphere long enough to completely vaporize — although it probably didn't look much like a manhole cover anymore by the time it escaped.
I don't think melting is the issue here. I think it literally disintegrates at those speeds. Like, this is Mass Effect mass driver level of impact with the atmosphere.
For reference, RICK ROBINSON'S FIRST LAW OF SPACE COMBAT: "An object impacting at 3 km/sec delivers kinetic energy equal to its mass in TNT."
Assuming the lid is travelling 55km/s, it's well beyond that point. The atmosphere it's travelling through is basically a solid at that speed. Even if it isn't heating due to the friction (and waiting for heat flow), it is heating due to the compressive force of being slammed into the atmosphere. It's very likely the whole thing vaporized.
But I could be wrong, and some alien SOB is going to have a bad day when the manhole cover slams into their ship in interstellar space.
Would vaporization slow the material though? Perhaps the end result wasn't a manhole escaping the solar system but a huge collection of microscopic metal fragments scattershot that direction. Which really makes the Mass Effect quote even more relevant to a huge amount of aliens somewhere.
Vaporization would certainly slow the material. It's transitioning kinetic energy into thermal.
Also, the vaporized iron would disperse outward rather than stay coherent.
It would spread outward a bit, but the entire kinetic energy and momentum in the system would remain the same. But, the more it broke apart, the more surface area it would have. The more surface area, the more surface exposed to heating. The more heating, the more it would break apart. I'm guessing that it was a silicon, iron and oxygen plasma without individual grains by the time it hit the upper atmosphere.
The atmosphere is just about 10 kg/m^2 in sectional density; the manhole cover was very likely higher than that, wouldn't that mean the cover's mass should have come out at the other side, intact or not?
It was being propelled by a nuclear blast. The speed was calculated from 1 frame of a high speed camera. It most definitely vaporized.