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Re: beginner question - from EU Perspective
Posted: Wed Feb 22, 2023 3:10 pm
by jacmac
This discussion about gravity and mass and pumice etc is way beyond my abilities.
However, I do have a question about PRESSURE deep in the earth (or any other solid body).
In a body of water or fluid, depth would be directly related to pressure. That makes sense.
But I don't understand assumptions of pressure deep under rocky bodies.
Any one passing under a BRIDGE of stone or rock would feel no pressure from the above structure.
So, deep in the earth how can depth be related to pressure when the lateral forces
in the structure above are not known ?
This has always bothered me.
Any comments ?
Re: beginner question - from EU Perspective
Posted: Wed Feb 22, 2023 4:52 pm
by Aardwolf
jacmac wrote: ↑Wed Feb 22, 2023 3:10 pm
This discussion about gravity and mass and pumice etc is way beyond my abilities.
However, I do have a question about PRESSURE deep in the earth (or any other solid body).
In a body of water or fluid, depth would be directly related to pressure. That makes sense.
But I don't understand assumptions of pressure deep under rocky bodies.
Any one passing under a BRIDGE of stone or rock would feel no pressure from the above structure.
So, deep in the earth how can depth be related to pressure when the lateral forces
in the structure above are not known ?
This has always bothered me.
Any comments ?
The bridge is protecting you from the pressure above you. You're still surrounded by atmospheric pressure. As for deep in the Earth, if you found a strong enough rock bubble you would be ok (like a submarine in the ocean), however, after about 1% down through the crust, it all likely turns liquid magma.
Re: beginner question - from EU Perspective
Posted: Wed Feb 22, 2023 4:54 pm
by Aardwolf
Here's Epimethus with an apparent density of 0.64 g/cm;
https://solarsystem.nasa.gov/moons/satu ... /in-depth/
NASA wrote:They are both thought to be composed of largely of water ice, but their density of less than 0.7 is much less than that of water. Thus, they are probably "rubble piles"—each a collection of numerous pieces held together loosely by gravity.
Really? Is that what this is? The internal loose material should at least be compacted to ice at 0.9 g/cm. Snow has virtually zero compression strength.
Re: beginner question - from EU Perspective
Posted: Thu Feb 23, 2023 9:53 pm
by Arcmode
0.7 is the same density as cardboard. I would love to take a sample from the surface.
Re: beginner question - from EU Perspective
Posted: Mon Feb 27, 2023 4:35 pm
by Aardwolf
Arcmode wrote: ↑Thu Feb 23, 2023 9:53 pm
0.7 is the same density as cardboard. I would love to take a sample from the surface.
No need to wait or even speculate. It will be exactly what we already collect from everywhere else. Dense rocks.
Hayabusa-2 collected some samples from "snowball" Ryugu at 1.2 density. And guess what it brought back, rocks;
https://www.bbc.co.uk/news/science-environment-55315502
BBC wrote:chunks of rock...
Be careful what your lying eyes tell you BBC, didn't you know Ryugu is supposed to be made out of water.