Timeline for Could a planet ever end up with a doughnut hole in it?
Current License: CC BY-SA 3.0
10 events
| when toggle format | what | by | license | comment | |
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| Jan 18, 2013 at 7:42 | comment | added | randunel | And... the planet would be knocked off orbit, of course :D | |
| Jan 18, 2013 at 7:41 | comment | added | randunel | Indeed, but we are not talking about Earth. Assuming a fast-spinning planet which does not have a spheric shape due to its axial velocity. Also, in ideal conditions, the planet would consist of lightweight materials, it would be moving in a direction opposite to the incoming body. The "projectile" would then be a heavyweight bullet-shaped axial-spinning body. Assuming the ideal conditions, I think it is possible, although the doughnut will not last for too long and the debris may end up being more then what's left :) | |
| Jan 17, 2013 at 15:34 | comment | added | Zo the Relativist | @randunel: the Earth is actually spinning quite slowly, compared to gravitational forces. If it were spinning quickly, you'd weight significantly more in Oslo than you do in Rio de Janiero. | |
| Jan 17, 2013 at 15:19 | answer | added | Will Cross | timeline score: 2 | |
| Jan 17, 2013 at 14:34 | comment | added | randunel | I understand that the forces would be huge, but what if the resulting doughnut-shaped planed would then be spinning fast enough to keep the doughnut hole empty for a while? | |
| Jan 17, 2013 at 12:03 | comment | added | mmc | @JohnRennie I think the projectile would have to be hyperdense to bore through the planet. Very roughly speaking, it's mass should be greater than the one of the column of rock that is being displaced. For small impactors with size $D$ boring through the Earth's diameter, their density needs to be about $5\mathrm{\frac{g}{cm^3}}\frac{12000 \mathrm{km}}{D}$. | |
| Jan 17, 2013 at 11:15 | comment | added | John Rennie | This is a good question. As Luboš says, any hole would be quickly filled in, but the question is whether any projectile could bore a hole or whether it would just blow the planet apart. I suspect that even a small size projectile would just blow the planet apart rather than bore a hole through it, but I don't know of a proof of this. | |
| Jan 17, 2013 at 9:27 | comment | added | Luboš Motl | Incidentally, the speed or energy carried by the bullet that would be enough to puncture the Earth would be so insane that it's impossible not just in practice but one could perhaps say that even in principle. Things that are too fast also burn in the atmosphere because of the friction, or they melt and burn while going through the Earth. At any rate, these fast enough bullets would melt the Earth's rock so the resulting liquid would quickly fill the room behind the bullet and there would be no air/vacuum-filled hole left. | |
| Jan 17, 2013 at 9:24 | comment | added | Luboš Motl | You may create a hole through a planet but the resulting object won't be sufficiently stable. The pressures near the hole will be huge and will drive the material to rupture and rearrange itself so that the hole is filled. That's particularly clear for the Earth whose (outer) core is liquid. Obviously, a hole in a liquid won't stay for too long. Quite generally, planets and celestial bodies want to reduce the gravitational potential energy and they do so by converging towards the perfect spherical/ellipsoidal shape. Every earthquake brings the Earth closer to a perfect sphere, too. | |
| Jan 17, 2013 at 9:02 | history | asked | Aaron Anodide | CC BY-SA 3.0 |