Hisses at Mission of Gravity being called Hard Sci-fi - more seriously, tho - You might want to check some of the discussion around that novel. It is fascinating.

Also, that novel opens up an incredible discussion about what even is hard sci-fi - is it a form of making fiction, or is it scientifical correctness?

Certainly a lot of work needs to be done by the "reasonably" in my description :-p Personally I judge the hardness of the work more on the author's intention to attempt scientific rigour, than on their actual success at it. Yes he got the polar gravity wrong by a factor of three, but at least he made some attempt to calculate it. I'm certainly not going to throw stones at his spherical integral glasshouse :-p

There are other issues with Mission of Gravity, but don't get me wrong - it is a fascinating read for sure.

This is probably not the place for this but what in the name of Jesus is this planet made of ? I dont think you can get 700G on a self gravitating body with normal nuclear forces. Like you get enormous acceleration on say white dwarf´s but those are held up by Electron degeneracy pressure. Does the planet have like a fragment of a Neutron Star as its core ? Otherwise i dont think you can get this

@ErikHall I think the idea is that it's the rocky core of a super-Jupiter gas giant whose gas got ablated off by the force of its star's solar winds but kept spinning at the same rate. Without the continual downwards force of all that gas the centripetal force at its equator could bulge it outwards.

@KEY_ABRADE pretty sure that dosnt work. The cores of Gas Giants are made, we think, out of well Iron, Copper and such but also a lot of Metallic Hydrogen. Which cannot exist without a massive atmosphere pounding down.

@ErikHall The metallic hydrogen stops being metallic if all the mass above it gets ablated away by the planet's host star, and then I would imagine it get blasted away itself. Think of the rocky core as a "sponge" whose gaps are filled with metallic hydrogen; once there's not enough pressure the metallic hydrogen turns into normal-phase hydrogen and the "sponge's" gaps collapse under gravity, turning it into a ball of rock.

@KEY_ABRADE i just did some math. Even if we assume the core was basically made of pure Tungsten, no element is strong enough to resist such a strong pull of gravity. At 700 Gs it only takes a vertical column of Tungsten a few kilometers tall to overcome the compressive strength. So any other material too would just start to implode. At some point Electron Degeneracy pressure would prevent the further collapse. But afaict no element could support such a dense object.

@JBH I don't agree that this question is about a 3rd party world. The first paragraph just says where the OP got their idea of "humans in high gravity" from. In my eyes the question itself is sufficently disconnected from the "Mission of gravity". I agree on b) and c) though

a) I'm actually trying to balance a trading game taking place on multiple worlds, and wanted to encourage trade between planets with different gravities; I read MoG as research, not the other way around! Re b) it's ironic that I included my thoughts on isotope separation precisely to avoid falling to demonstrate "should include research... What ideas have you considered" from c); it feels to me that those two rules are somewhat incompatible. b) and c) are fair criticisms, however, my apologies.

@JBH I have to side with datacube here. The question illustrates the situation, but does not request a book specific reason. Leaving the book out would still have a valid question. That is impossible with questions like "how would Thor's hammer in comic xyz work?", which should rightfully be VTC.

@datacube It's not our job to look through what the OP says and find a way to answer any question. It's the OP's job to understand the policies of where they are. At 8K rep, the OP has enough experience to either know better or know how to find out. This stack helps people build imaginary worlds of their own creation. I can't find such a world anywhere in the OP's question.

@Stephen "I'm actually trying to balance a trading game…" Why didn't you explain that and how the issues of the 3rd party/commercial world related to your game? Why didn't you explain the relevant conditions of your game that would affect the circumstances of the 3rd party/commercial world? As frustrating as it may seem, asking how the ideas of someone else's world can be generalized is a form of plagiarism. Fair use comes into play when those ideas are modified to meet the needs of your use. As written at the time I made my comment, I could find no conditions warranting modification.

@JBH I wouldn't consider "hey I read this book and I find the idea of a high gravity planet fascinating. I want to build a world with such a planet. But the reason of the book is bad so I need a better reason for humans to settle there." as plagiarism. I would call it inspiration. I doubt OP wants to rewrite the same book and just add a better reason to be there. If that would be plagiarims, then every story but the first to use the idea of hyperspace as FTL would be. As would be all stories about a "jungle planet" or a "city planet". (cont)

@JBH (cont) Giving all the story involved would be just unneccessary bloat to the question and probably cause it to be VTC "story based".

@Stephen I think the point JBH has with your given answer is, that you do not explain why your answer is not the actual answer for you and go with that idea. And for c) you would need to give a few additional constraints on the expected answer. Most especially it would help to talk about available technology in your universe since otherwise the "science based" constraint can't be fullfilled. Also I'd advice you to add a paragraph that you handwave the existence of said planet... If that would go against the "no edit that invalidates answers" policy... yeah the policies...

@datacube That's not what the OP said. That's what you're assuming (considering only the qeustion and none of the comments).

I for one welcome the anecdote. We get plenty of dry, uninspired questions around here. And when you aren't parsing the text like a bureaucrat, it's clear we're not being asked about a 3rd party.

do you mean 70G at 700G the planet should undergo nuclear fusion on a large scale. and I am fairly sure it has to spinning at relativistic speeds to get that kind of surface gravity range. Have you tried asking about the existence of such a planet, because the answer might be for making antimatter.