# How Does Mining Affect the Gravity of a Hollowed-Out Planet?

• Khatti
In summary, Hollowing out an earth-sized planet would reduce its gravity. It would be difficult to do perfectly, and there would be some major consequences for the surface.
Khatti
I'm working on a planet that is earth-sized, but has been essentially a dead stone for millions of years: no volcanic activity, the core has completely cooled down, the atmosphere has long since drifted off. In turn it has been mined for so long that a sixth of its mass has been dug up and shipped off. Much of that mass has actually come from the core. Does anyone have any thoughts how hollowing out an earth-sized planet would effect its gravity?

Thanks to Gauss's law...

Assuming these tunnels are more or less evenly dispersed throughout the planet, and assuming that the planet is more or less uniformly dense, then the force due to gravity is proportional to the radial distance from the core.

If the core is hollowed out, but the the rest of the planet is more or less still radially symmetric, then throughout the hollow core, the net gravitational force will be zero, and you'll be able to float throughout the hollowed core (assuming the mass of air in the core is negligible).

Khatti said:
I'm working on a planet that is earth-sized, but has been essentially a dead stone for millions of years: no volcanic activity, the core has completely cooled down, the atmosphere has long since drifted off. In turn it has been mined for so long that a sixth of its mass has been dug up and shipped off. Much of that mass has actually come from the core. Does anyone have any thoughts how hollowing out an earth-sized planet would effect its gravity?
simple, since a sixth of the mass has been removed, and from the core, the gravity at the surface will be reduced by a sixth.

It is highly unlikely that the cored planet would remain structurally intact, unless the coring is perfectly distributed as @jfizzix notes. But more likely, slight mass unbalances would cause it to collapse in parts, with obvious devastation to the surface as thousands of kms of depth subside. This is going to take some time, and will likely be in parts, not all at once. It will eventually be pretty much spherical, with some massive craters that remain because there is no continental shift to recycle the mantle and no air to erode the surface features.

It's gravity would decrease, obviously, but because the radius would as well, it might not be as straightforward as being exactly one sixth less as @greswd notes, but that's probably close enough.

Khatti
Tghu Verd said:
It is highly unlikely that the cored planet would remain structurally intact, unless the coring is perfectly distributed as @jfizzix notes. But more likely, slight mass unbalances would cause it to collapse in parts, with obvious devastation to the surface as thousands of kms of depth subside. This is going to take some time, and will likely be in parts, not all at once. It will eventually be pretty much spherical, with some massive craters that remain because there is no continental shift to recycle the mantle and no air to erode the surface features.

It's gravity would decrease, obviously, but because the radius would as well, it might not be as straightforward as being exactly one sixth less as @greswd notes, but that's probably close enough.
yeah, it would actually shrink a lot, and the size would depend on the density profile, which itself is dependent on the internal pressure, which is dependent on the internal gravitational field, and which is dependent on the density profile!

it'll also depend on the strength of the planet's composition. Realistically a swiss-cheese planet would be super unlikely to be possible.

## 1. What is "Gravity in a Swiss Cheese ball"?

"Gravity in a Swiss Cheese ball" refers to the concept of gravity in a hypothetical scenario where the universe is shaped like a Swiss cheese ball, with holes or voids in the structure.

## 2. How does gravity work in a Swiss Cheese ball?

In a Swiss cheese ball universe, gravity would still function as it does in our current understanding of physics. Objects with mass would still exert a gravitational force on other objects, and larger objects would have a stronger gravitational pull.

## 3. Would gravity be affected by the holes in a Swiss Cheese ball universe?

Yes, the holes in a Swiss cheese ball universe would affect the distribution of matter and therefore the gravitational pull in different regions. The holes or voids may have weaker gravitational forces compared to areas with more matter.

## 4. How would the presence of multiple holes in a Swiss Cheese ball universe affect gravity?

The presence of multiple holes in a Swiss cheese ball universe would create a more complex gravitational field. The gravitational pull would vary in different regions depending on the distribution of matter and the size and number of the holes.

## 5. Is there any scientific evidence or theories about a Swiss Cheese ball universe?

Currently, there is no scientific evidence or theories to support the existence of a Swiss cheese ball universe. It is a hypothetical concept used to explore different ideas and possibilities in physics and cosmology.

• Sci-Fi Writing and World Building
Replies
0
Views
925
• Sci-Fi Writing and World Building
Replies
0
Views
370
• Sci-Fi Writing and World Building
Replies
21
Views
1K
• Sci-Fi Writing and World Building
Replies
87
Views
5K
• Introductory Physics Homework Help
Replies
4
Views
595
• Sci-Fi Writing and World Building
Replies
9
Views
2K
• Classical Physics
Replies
9
Views
953
• Sci-Fi Writing and World Building
Replies
6
Views
995
• Sci-Fi Writing and World Building
Replies
15
Views
2K
• Sci-Fi Writing and World Building
Replies
7
Views
2K