Designing a planet denser than earth

[mr friendly guy]

Just a question for those more astronomy inclined. If I wanted to design a planet for a sci fi setting roughly earth size, but with more mass, hence I can explain away the stronger inhabitants.

Presumably the planet will have a higher percentage of denser materials, but doing the pre crisis Superman route of a core of uranium seems silly.

So how would you go about doing this?

[Sea Skimmer]

I've thought about the same thing more then once. We get metal from stars making it, and as I understand it the longer the universe lasts the more metal is present vs. lighter elements as stars form from the debris of older stars that went nova. So a planet that forms later then earth, or forms in an area with a higher ratio of older stars and supernova debris could plausibly have a higher metal content from the get go. When it comes down to the details I don’t think you need anything exotic, just a larger iron core would increase density considerably.

The trick is, if the planet is denser and has more gravity when it forms, it should want to keep pulling in more debris from a wider band of space as it orbits its star then earth did as it clears its orbit, and thus will easily grow to be larger then earth sized, all else being equal, which might remove its higher average density. So you need the situation to have evolved in such a way that you had a higher proportion of metal, and yet not sufficient total material present to create an over sized planet compared to earth. You might get that from random chance in system formation, the universe has an awful lot of choices of star and system, or maybe from large asteroids or other heavenly bodies mopping up gas and dust that otherwise would have joined the metal planet. Having a very large moon might help suck up the material, or at least logically that makes sense to me. That extra material might also just still be present in the form of asteroids ect... and eventually end up as part of the planet as asteroids impact over time but that could involve a billion years ect kind of timeframe…. enough that it does not matter for storytelling purposes. The earth is still growing afterall, I think, or at least I thought I read that net gain of mass from meteorites raining down is higher then the rate of loss of gas mass as hydrogen and helium float off the planet.

[Darth Tedious]

I'm no astronomer, but having a quick glance at an old chemistry book...

You wouldn't need a uranium core if you wanted that level of ridiculous gravity- gold and tungsten are both slightly denser than uranium (masses of 19.3g/cm3 and 19.4g/cm3 respectively, 19.07g/cm3 for uranium).

As Sea Skimmer said, just having a denser core of iron would make a difference.

You could also have high percentage of cobalt, copper, and nickel in your planet. They all mass slightly more than iron.

[mr friendly guy]

Would this higher content of iron be accessible for say pre industrial societies up to societies with technology equivalent to current day mining companies? Or will the iron be buried too deep to mine?

[Darth Tedious]

Last I heard, we weren't mining the Earth's mantle with current technology, let alone the core.
What your peoples can mine will depend on how high the metal content is in the crust.

But yeah. Hell, if there's way higher iron content in the crust, there's no reason an iron age society wouldn't have access to awesome amounts of it.

It doesn't have to be buried very deep, either. Look at mining in iron-rich areas like the Pilbara. Modern mining technology would kick arse on Mars.

Blegh, I'm rambling a bit. Hope some of it helps.

[Darth Tedious]

Thought: How high would you want the gravity to be? Playing around with the Planetary Parameter Calculator, looks like you can get a realistic planet with 1.5G, not too much bigger than Earth (though it would be almost twice Earth's mass). If you set a goal density for your planet, you could play around with chemical compostion to acheive it.

[mr friendly guy]

I want the human settlers on the planet to be several times stronger than the average human on earth. Basically these humans have lost most of their advanced technology and are experimenting with magic. My universe is one of those where "magic" and technology co exist, eg like Shadowrun, Might and Magic etc.

I want to be able to justify fight scenes where people are thrown back several metres with a blow, ie like Captain America (movie) level of strength. A lot of combat sequences in television series have scenes where "average" humans are thrown back to hit a wall hard and pick themselves up to fight again, say Charmed (snigger). I at least want an explanation for why the average humans are so strong. I figured 10 x the average human as an upper limit should more than cover it, although I haven't really run the calculations. I suppose it becomes more complicated because gravity is also higher, so presumably the humans would need to be stronger than Earth bound humans in a higher magnitude than the gravity is stronger than Earth's, unless the fight scene occurs on a different planet with 1 G.

[Batman]

Isn't achieving superstrength via higher gravity sort of self-defeating? Yes, the people who grew up on a planet with, say (arbitrarily assuming a strength increase by a factor of 10 would require a surface gravity of 10g) a surface gravity of 10g are bound to be massively stronger than modern day humans, but not only are they bound to be massively denser too, but them having to work inside that 10 g gravity well sort of cancels out their strength advantage on top of that, doesn't it?

Not that it ever really made sense for Clark either but back when they tried to explain his superstrength with Krypton's higher gravity he had been transplanted to Earth. Given the loss of technology I assume your setup happens onplanet.

[Zor]

One of the things from the Honorverse was that Grayson was made of denser stuff than earth (but had comprable gravity), a fact that made colonizing the place really dificult because much of that stuff was highly toxic.

Zor

[Lord of the Abyss]

Just a question for those more astronomy inclined. If I wanted to design a planet for a sci fi setting roughly earth size, but with more mass, hence I can explain away the stronger inhabitants.

Presumably the planet will have a higher percentage of denser materials, but doing the pre crisis Superman route of a core of uranium seems silly.

So how would you go about doing this?

How about this. During late planetary formation, the proto-planet has a close encounter with an object of similar size; a glancing impact nearly powerful enough to destroy it that blasts off the majority of its lighter elements. It manages to retain/re-accumulate enough lighter elements to form an outer crust that can support life, but is essentially a ball of iron with a thin surface coating of lighter material. In Earth terms, it's crust and core with little or no mantle.

[Cesario]

I want the human settlers on the planet to be several times stronger than the average human on earth. Basically these humans have lost most of their advanced technology and are experimenting with magic. My universe is one of those where "magic" and technology co exist, eg like Shadowrun, Might and Magic etc.

I want to be able to justify fight scenes where people are thrown back several metres with a blow, ie like Captain America (movie) level of strength. A lot of combat sequences in television series have scenes where "average" humans are thrown back to hit a wall hard and pick themselves up to fight again, say Charmed (snigger). I at least want an explanation for why the average humans are so strong. I figured 10 x the average human as an upper limit should more than cover it, although I haven't really run the calculations. I suppose it becomes more complicated because gravity is also higher, so presumably the humans would need to be stronger than Earth bound humans in a higher magnitude than the gravity is stronger than Earth's, unless the fight scene occurs on a different planet with 1 G.

You could just posit some straight genetic engineering for improved strength and durability before the onset of the technological dark age, and leave them on a planet with earth-normal gravity.

[CaptainChewbacca]

If the surface gravity gets much past 1.6 earth gravities, I believe it will be strong enough to hold on to helium and hydrogen, which seriously messes up your atmospheric chemistry.

[Dwelf]

Are you planning to set the story on this world or is it just the home planet and they have used their magic to get to a lower gravity planet. If the planet is the setting then the increased gravity is going to make it very hard to throw people several metres. You may want to look at taking the gravity in the other direction. If you lower the gravity slightly and increase the strength slightly you would probably have the effect you are looking for.

[mr friendly guy]

To answer the questions in no specific order

1. I do plan to use this planet as a setting. Basically the humans have settled on the planet and are adapted for it. I want stronger humans not just for fight scenes in that planet, but eventually in case they meet humans from other parts of the Old Human Federation type government who still have things like FTL technology etc.

If necessary I will just say psionics blah or magic blah to explain away the discrepancy in the extra strength among the humans and non humans.

2. I did think about using the genetic engineering idea, but figured it would be better to say that they were genetically modified to live on the higher gravity world, but they gave the humans extra strength to be on the safe side. This way I can still justify the fight scenes among "ordinary" inhabitants.

If the humans were modified to be strong but settled on a world with similar gravity to Earth, I have to explain in the backstory why they needed to be modified in the first place.

3. If 1.6 G is the upper limit before I have to throw in "magic" to have similar atmospheric conditions, I think I will just leave it at around 1.5 G and roughly Earth's size, maybe a little bigger.

4. If all it takes is just higher amounts of denser material with an explanation, I could use say Sea Skimmer's explanation and say that the planet is "rich" because it has high amounts of gold,iron etc. Of course gold might be harder to justify as a medium of exchange if its not as rare, but I figured since they are descended from humans which use to have star ships, they use a fiat currency as well.

[Darth Tedious]

When I played with the Planet calculator, I had 1.5G with a diameter of 14250km.
Planetary mass was 1.119E+25kg.

Average density wasn't much below that of iron though.

[Darth Wong]

Everyone always assumes that higher gravity would make people super-strong. They forget that higher gravity would also mean a denser atmosphere. A creature accustomed to higher gravity would probably flop about like a dying fish if he was put into our low-gravity environment with its low-pressure atmosphere, the same way we are rendered weak and delirious at high altitudes.

[Simon_Jester]

It occurs to me that in one of the the oldest SF stories I know of that justifies greater physical strength with "heavy-worlder," the high-gravity Valerians perform nearly all their great feats of strength while wearing armored space suits, and tend to bitch about how thin the air normal people breathe is.

A pity that part's been forgotten in the years since Galactic Patrol, I guess.


Also, life on the high gravity planet wouldn't look like wire-fu with people getting thrown huge distances through the air, because they fall to the ground so much faster. If a man's strong enough to throw another man sideways at 2 m/s, from about two meters off the ground, then in one gravity they'll travel about 1.2 meters sideways before hitting the ground after falling for about 0.6 seconds.

Make the same man four times as strong because he lives in a gravity four times greater, and he now throws a man sideways at 8 m/s... but he's still throwing from two meters off the ground, and at four gravities the guy will fall to the ground within about 0.3s. The distance is only 2.4 meters, and you hit the ground a lot harder.

[andrewgpaul]

Do you really need a larger, denser, whatever planet to explain stronger inhabitants? How much stronger are you talking? Apes such as chimpanzees are significantly stronger, weight for weight, than humans, as I understand it, and they evolved right here. Unless it's somehow relevant to the plot why/ these creatures are stronger than humans, does it really need explained?

[Simon_Jester]

On the other hand, the nonhuman apes also evolved to do things like swing through trees a s a routine way of getting around. That takes a level of athleticism that you just don't see in humans. And the nonhuman apes aren't tool users, so being ridiculously strong is their main defense against predators. Humans evolved to live on plains, throw rocks at things, and do a lot of long distance running instead.

So if you have a planet where the natives are descended from something like a plains ape, but are built like gorillas for strength, there's probably a reason.

[Darth Wong]

Do you really need a larger, denser, whatever planet to explain stronger inhabitants? How much stronger are you talking? Apes such as chimpanzees are significantly stronger, weight for weight, than humans, as I understand it, and they evolved right here. Unless it's somehow relevant to the plot why/ these creatures are stronger than humans, does it really need explained?

That's a good point; we humans are weak because our evolutionary background emphasized fuel efficiency, for lack of a better term. There's no reason to assume that must be equally true for every other humanoid creature in the universe.

[Connor MacLeod]

I've always thought that people trying to inhabit a heavy-gee world would need extensive modification (genetic, cybernetic, magical, or whatever.) to survive. I mean it's more than just putting more muscle onto the body. The skeleton would have to be able to withstand the extra strength your hypotehtical heavy-gravity guy would have, as well as sustain the extra weight in that enviroment. Moreover, you'd need to be physically tougher to survive the greater abuse on said body, and you would need more energy to fuel that body. And if the energy intake is increased, how does the body deal with the excess heat? And so on.

[Darth Wong]

I've always thought that people trying to inhabit a heavy-gee world would need extensive modification (genetic, cybernetic, magical, or whatever.) to survive. I mean it's more than just putting more muscle onto the body. The skeleton would have to be able to withstand the extra strength your hypotehtical heavy-gravity guy would have, as well as sustain the extra weight in that enviroment. Moreover, you'd need to be physically tougher to survive the greater abuse on said body, and you would need more energy to fuel that body. And if the energy intake is increased, how does the body deal with the excess heat? And so on.

The evolutionary development of bipeds would be discouraged in such an environment.

[mr friendly guy]

Do you really need a larger, denser, whatever planet to explain stronger inhabitants? How much stronger are you talking? Apes such as chimpanzees are significantly stronger, weight for weight, than humans, as I understand it, and they evolved right here. Unless it's somehow relevant to the plot why/ these creatures are stronger than humans, does it really need explained?

I was hoping to justify wire fu like scenes, or Jedi / Sith type battles. Obviously the combatants are trained etc, they aren't skillful pugilists purely because of a heavier world. As I said, lots of shows have allegedly normal humans punched and thrown around into walls and get up to fight again. In real life one punch is enough to kill a person, such that the government of my state of Western Australia has legislated against these "one punch" deaths.

So my initial thought was that stronger inhabitants which includes humans modified to live in that world, with also the indigenous inhabitants would justify such scenes. But Simon Jester's post has left me a lot to think about. It may be I have to simply say that the indigenous life form are the equivalent of super strong chimps and humans are modified to be strong and tough for some other reason.

[mr friendly guy]

Ok lets think about another aspect. I can come up with some other explanation to justify wire fu scenes even if I just go magic blah blah or psionics blah blah. I can even accept Earth equivalent gravity. In fact even with 1 G there is no one someone will glide that way as say a character virtually flying would do. So I most probably need another explanation anyway.

But say if I wanted the world to have high amounts of say gold or iron, and hence by default would make the planet denser but around equivalent Earth size. How many G's can I make it to still get away with wire fu scenes. Obviously when a character jumps, I have to use magic or psionics or whatever to justify how they can move up against a 1G or higher so easily. However using Simon Jester's example, when another character knocks one down from a height, I don't want them falling too fast from a thematic aspect, because it just ain't wire fu if they fall to the ground in a ridiculously short time.

So using displacement = initial velocity (zero as they just start falling) x time +(acceleration x time squared / 2).

If I say the character starts falling from a height of 3 metres, with acceleration of 0.9 metres / second squared, ie 1 G I worked out it takes around 2.58 seconds to hit the ground. At 1 metres / second squared roughly 1.1 Gs it takes around 2.45 seconds. At 1.2 Gs at 1.08 metres/ second squared it takes 2.35 seconds. That extra half a quarter of a second won't make much difference thematically. Have I done my maths right? Its been ages since I had to do such physics calculations.

[Batman]

Just because they were designed for a high g world/one where significantly higher than normal human strength was deemed desirable doesn't mean they actually wound up there. While it's pretty cliche their colony ship having an accident/human error/malfunction etc. en route and having to crashland is pretty cliche it would go a ways to why the lost so much if not all of their tech base.
Plus there's always the Manpower slave transport riot approach-they were designed for heavy labour/pitfighting/whatever, managed to hijack the ship but crashed it due to having no real clue how it worked.