Forum: scifi.stackexchange.com
Tags: <hard-sci-fi><gravity>
Title: In science fiction, which planet with lifeforms has the largest gravitational force?
Question: I've just started reading  Foundation  and Gaal Dornick has landed on Trantor for the first time and notices that:   The air seemed thicker here, the gravity a bit greater, than on hishome planet of Synnax...   This prompted me to wonder,  what is the highest gravity planet mentioned in science fiction that has lifeforms?  Edit 1: I am specifically asking about planets with solid surfaces.  Edit 2: I am referring to the gravitational force at the surface.

Answers:
sents: text: Probably Hexanerax 2 in Childhood's End by Arthur C Clarke, given that Robert L Forwards's Dragon's Egg is a neutron star not a planet.
text: Here's how it is described: The planet was absolutely flat.
text: Its enormous gravity had long ago crushed into one uniform level the mountains of its fiery youth--mountains whose mightiest peaks had never exceeded a few metres in height.
text: Yet there was life here, for the surface was covered with a myriad geometrical patterns that crawled and moved and changed their colour.
text: It was a world of two dimensions, inhabited by beings who could be no more than a fraction of a centimetre in thickness.
text: That's pretty much all we know about it -- it's a throwaway vision, not the setting for any of the novel.
text: (Hal Clement's Mesklin from Mission of Gravity is an obvious contender, but its gravity is a mere 3G at the equator where the known life is, and 665G at the poles, which is probably still less than Hexanerax 2 as described.)
answer_details: author: scifi.stackexchange.com/users/23/Mike Scott
score: 30
sents: text: I'll venture that the winner is none other than our old favourite; Krypton .
text: Without focusing on specific numbers, the surface gravity on Krypton would have to be tens of thousands of times heavier than Earth to meet the description below.
text: It was "The Black-Hole Planet."
text: Nothing ever left.
text: It was as dense as a newborn star and as dark as the pit.
text: From a more conventional planet with crusted frozen oceans, life should at the very least have reflected so much that astronomers in nearby systems might at first have mistaken it for a star.
text: It was so heavy that space itself contracted around it.
text: A dull green glow, the backwash of starlight that collected in its atmosphere, reflected downward to streak Krypton's daytime sky with red-shifted luminous clouds and light its nights with a phosphorescent pink.
text: The light radiated from every horizon.
text: The days were barely brighter than Krypton's nights.
text: It took an enormous expense of energy to launch anything from the world's surface.
text: Even a nuclear-powered vessel designed to accelerate across lightyears of space needed to tap the thermal energy of the planet's underground in order to trigger a reaction big enough just to escape Krypton's terrible attraction.
text: Even on a world whose population's profligate use of energy had actually slowed the planet's self-destruction, Jor-El realized that his use of so much power in one burst would certainly attract attention.
text: He gave himself the chance to make the only test of his prototype starcraft.
text: If we're just looking at heavyworld sci-fi in general, then you can't got far wrong with Flux by Stephen Baxter.
text: The main characters are tiny humans living inside the surface of a neutron star rather than merely living on the surface, like the wimpy lifeforms in Dragon's Egg
answer_details: author: scifi.stackexchange.com/users/20774/Valorum
score: 21
sents: text: I don't remember the name of the story; but you didn't ask that.
text: I believe that the answer might be Jupiter .
text: Isaac Asimov wrote a short story in his robots series about the "ZZ" line of robot,which was designed to travel to the surface (!) of Jupiter.
text: Three of them traveled there in a non-airtight spaceship(rather than try to build something that could withstand the atmospheric pressure).
text: They encountered creatures that were sufficiently
text: advancedthat they attacked the robots with weapons (although not effectively).
answer_details: author: scifi.stackexchange.com/users/30482/Peregrine Rook
score: 8
sents: text: By far not the one with the highest density (looking at Mike's and Richard's answers here), but Perry Rhodan issue #16, "Die Geister von Gol", was about a planet of 916g surface gravity, making it a #3 entry at the time of posting.
text: ;-)
text: Rhodan and his crew navigated the surface with tracked multi-purpose vehicles ("Shifts"), which needed their anti-gravs (usually used to let them fly) running at max output just to keep them mobile (and not crushing the crew).
text: I am not sure if you could call the beings they encountered "life forms" (and neither were the protagonists), as they seemed to be energy-beings, but they were attracted by the vehicle's shields (reacting to stimulus), and drained their power supply, growing in size in the process (feeding, growth), so let's call them "life".
text: The highest gravity planet to bear human life in the PR universe would be Oxtorne, a 4.8g world.
text: A shipwrecked crew of emigrants managed, with the help of genetic engineering, to adapt to the harsh environment of their world within four generations.
answer_details: author: scifi.stackexchange.com/users/25836/DevSolar
score: 4
sents: text: Not as much gravity as a neutron star, but Iain M Banks's The Algebraist features a race called the Dwellers who float around inside of gas giants throughout the galaxy.
text: ZanLynx mentioned in the comments the Hades Matrix from Alastair Reynolds's Revelation Space series, a neutron star that was somehow converted into an impossibly dense and powerful computer so that a long-dead race could go on living as programs within the matrix.
text: So they're not exactly life forms in high gravity, but maybe it still counts.
answer_details: author: scifi.stackexchange.com/users/22299/Robert
score: 1
sents: text: First Mesklin popped my mind from "Starlight" by Hal Clement.
text: It is a true planet (not a neutron star like Hexanerax2) and it has a solid surface (unlike the aforementioned gas giants), but it has a size of a smaller gas planet and a shape
text: so distorted that the strenght of the gravity on its equator is slightly different than on its poles.
answer_details: author: scifi.stackexchange.com/users/33716/mg30rg
score: 0
sents: text: Stephen Baxters Flux tells a story about a "human" civilization living on a neutron star.
text: Not really humans, but made by humans to be able to live on the neutron star.
answer_details: author: scifi.stackexchange.com/users/111721/Dennis
score: 0

Summary of the answers:
Hexanerax 2, Krypton, the planet in Flux by Stephen Baxter, and Oxtorne are all suggested answers to this question.
The possibilities are as follows: Hexanerax 2, Mesklin, Krypton, the Black-Hole Planet, Jupiter and Oxtorne. The planet in Flux by Stephen Baxter is also a contender.