Just saw Man of Steel for the first time (spoilers)

[danzibr]

One thing in particular caught my interest, and I wonder if any science-y people can shed light on the subject.

Near the end, when the baddies try to make Earth like Krypton, they do some funny business which is supposed to increase the Earth's gravity and mess with its atmosphere. Now my questions are

1) how would you strengthen a planet's gravity? Add mass without changing the volume, I assume. But uhh, how would that work?
2) what affects would strengthening the gravity have? Shrink our atmosphere? Crush animal and plant life which didn't evolve with stronger gravity?
3) related to 1, is it reasonable to have an Earth-size planet with stronger gravity (or similarly, a smaller planet with similar gravity)? Like, I assume the core would have to consist of denser metals, or maybe the core would have to be bigger, or something.

Thanks!

[Mando Knight]

It's been a while since I've seen the movie, but they're using their ship's Phantom drive as part of the operation, IIRC. Along with the gravitic pulses to compress the rock, it's probably injecting matter from the Phantom Zone back into reality, increasing the mass of the planet.

[Peelee]

One thing in particular caught my interest, and I wonder if any science-y people can shed light on the subject.
Keep in mind, I am not a smart man.

1) how would you strengthen a planet's gravity? Add mass without changing the volume, I assume. But uhh, how would that work?
Absolutely, you just add more mass. To add mass without changing volume, you take the mass and put it really, really close together.

2) what affects would strengthening the gravity have? Shrink our atmosphere? Crush animal and plant life which didn't evolve with stronger gravity
Probably. I don't quite see why they need to change the gravity, since if it's weaker, their structures should be more stable, and it's not like gravity will meaningfully affect flying people, but hey, let's change it why not. Pretty sure you're right; it's similar to that episode of Futurama with the treasonous Neutrals.

3) related to 1, is it reasonable to have an Earth-size planet with stronger gravity (or similarly, a smaller planet with similar gravity)? Like, I assume the core would have to consist of denser metals, or maybe the core would have to be bigger, or something.
I don't see why not. Mars is only 15% smaller than Earth, but only 38% the surface gravity compared to Earth, so if it moves one way, it can surely move the other as well.

Thanks!
No problem!

[gomipile]

The Earth's average density is about 5.5g/cc. The density of pure iron at standard temperature and pressure is 8g/cc. I think it would be reasonably possible for a planet with a much higher iron content and same radius as Earth to have a density of, say 7g/cc. Such a planet would have a surface gravity of about 1.28g. You could go higher by making a planet whose core and mantle were mostly lead or some other heavy metal, I suppose. I want to say that iron is more realistic, but this is a Superman story, so, meh.

[factotum]

You could increase a planet's surface gravity without adding any mass if you somehow compressed it down to make it smaller. Same amount of mass but at closer range (due to being smaller) would result in higher gravity. How you'd actually do that is anyone's guess, but it's at least as believable as adding huge amounts of mass to a planet--sourced from where, and added how?

[Peelee]

How you'd actually do that is anyone's guess

You just add a whole bunch of protons and neutrons. Stick 'em all together in the biggest ball you can. Simple, really.

[factotum]

You just add a whole bunch of protons and neutrons. Stick 'em all together in the biggest ball you can. Simple, really.

I'm glad that you completely ignored the most critical part of that sentence, which was the "sourced from where, and added how?" part--got an answer to that bit?

[Knaight]

The thing in question explicitly has a gravitic drive, and as such apparently can directly manipulate gravity (does this have any scientific basis, no, is it in a superhero movie anyways, yes). Just directly manipulating gravity seems like the easiest option here, particularly given all the side effects that would happen and don't happen if you compress earth significantly. All that crust has to go somewhere.

Also, gomipile: I looked up some density figures, and the outer core is 9.9 to 12.2 g/cc, with the inner core at 12.6 to 13.0 g/cc. Standard temperature pressure behavior is a pretty good assumption for solids at most conditions, but the sort of extremes at the earth's core is not most conditions. Whether the inner core is even solid per se is disputed, with the other possibility being a super dense plasma. Apparently being at about 6000 K (which isn't really that extreme) and 3.6 million atm (which is) is enough to dramatically diverge from STP behavior.

[Peelee]

I'm glad that you completely ignored the most critical part of that sentence, which was the "sourced from where, and added how?" part--got an answer to that bit?

Look, I solved half of it for you, I can't be expected to have all the answers.

Besides, I hear the universe is full of protons.

[Mando Knight]

I'm glad that you completely ignored the most critical part of that sentence, which was the "sourced from where, and added how?" part--got an answer to that bit?

The World Engine was linked up to their craft, which is equipped with a FTL drive that works by shunting them through the Phantom Zone. From that, it's easy to make the jump that they can source some matter from that extradimensional realm using their ship's equipment.

[Tvtyrant]

It just makes a particle and that particles anti-particle at the same time, and sends them in opposite directions. One ends up making the Earth bigger, the other one gets sucked into the Phantom Zone for all eternity.

Magic up the vacuum force and anything is possible!

[Wardog]

Densities of various rocks and minerals: (http://geology.about.com/cs/rock_types/a/aarockspecgrav.htm)

Minerals and metals:
Quartz 2.65 g/cm3
Feldspar 2.55-2.76
Calcite 2.71
Olivine 3.27-4.27
Pyrite 5.02
Magnetite 5.18
Hematite 5.26
Copper 8.9
Gold 19.32
Iridium 22.42

Rocks:
Sandstone 2.2 - 2.8
Limestone 2.3 - 2.7
Granite 2.6 - 2.7
Basalt 2.8 - 3.0

Density of the layers of the Earth: (http://hyperphysics.phy-astr.gsu.edu/hbase/geophys/earthstruct.html)
Crust: 2.2 - 2.9
Mantle: 3.4 - 5.6
Core: 9.9 - 13.2

Having more metals, ores, and rocks and minerals containing them would make the planet denser, and hence have a higher gravity.

(Though I don't know enough about planetary formation to say whether having more metals in the material the planet formed from would result in a denser crust with more usable ores, or if they would all sink to the core).

[factotum]

(Though I don't know enough about planetary formation to say whether having more metals in the material the planet formed from would result in a denser crust with more usable ores, or if they would all sink to the core).

There's a process called planetary differentiation which means the denser stuff will tend to sink to the core while the planet is entirely molten--this is why the Earth's core is mostly iron, while the crust is mostly silicates. Some small pieces of the heavier stuff will get carried along with large masses of lighter material, which is why you can still find iron and uranium in the crust--if the differentiation process was perfect there just wouldn't be any heavy metals up here.

[danzibr]

Gold 19.32
Iridium 22.42

[...] Core: 9.9 - 13.2
This makes it look like the core has a lot of gold and iridium. I always heard it was primarily nickel and iron. Is there something going on here with like extreme pressure making it denser than normal?

[hamishspence]

I don't see why not. Mars is only 15% smaller than Earth, but only 38% the surface gravity compared to Earth, so if it moves one way, it can surely move the other as well.



Mars is barely more than half Earth's diameter:

https://en.wikipedia.org/wiki/Mars

but it is true that, because it's less dense than Earth, its surface gravity is lower than that an Earth-density Mars-sized object would have.

[Peelee]

Mars is barely more than half Earth's diameter:

https://en.wikipedia.org/wiki/Mars

but it is true that, because it's less dense than Earth, its surface gravity is lower than that an Earth-density Mars-sized object would have.

This'll teach me to not write down what source I used or document the math so I can see where I messed up. Also, it's quite handy that wikipedia documents the planetary measurements in relation to Earth as well. Wish I knew that before I just did a quick and dirty googling.