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 his home 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.

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    There have been some stories with zeppelin-style lifeforms that float around in the atmospheres of gas giants, would you count those or are you asking only about planets with solid surfaces? – Hypnosifl Oct 7 '14 at 17:59
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    Plenty of examples here; tvtropes.org/pmwiki/pmwiki.php/Main/Heavyworlder – Valorum Oct 7 '14 at 18:21
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    To whoever keeps closing this as "too broad" - the community consensus so far on Meta is that it is NOT too broad. Please respect that. – DVK-on-Ahch-To Oct 8 '14 at 1:26
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    For clarification, does it HAVE to be a planet? The highest gravity environment in fiction which has lifeforms that I know of happens to be the surface of a star. – slebetman Oct 8 '14 at 4:39
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    @DVK Less people agree that it shouldn't be closed than it takes to close the question, so I think it would be fairer/more correct to say that there's discussion about whether or not the question should be closed, not that community consensus is that it shouldn't be. – Anthony Grist Oct 8 '14 at 12:20
up vote 27 down vote accepted

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. Here's how it is described:

The planet was absolutely flat. 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. Yet there was life here, for the surface was covered with a myriad geometrical patterns that crawled and moved and changed their colour. It was a world of two dimensions, inhabited by beings who could be no more than a fraction of a centimetre in thickness.

That's pretty much all we know about it -- it's a throwaway vision, not the setting for any of the novel.

(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.)

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    I was considering Dragons Egg, but yes it was a neutron star. However, if the OP was interested in lifeforms evolving in extremely high gravity it's definitely a recommended read. IMO it's one of the best books I've read. – queeg Oct 7 '14 at 14:28
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    I'm going to ignore that physics would never allow for a massive, yet completely flat celestial body. But, if the celestial body is completely flat, could it really be considered a planet? – Ellesedil Oct 7 '14 at 20:08
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    I don't think it's intended to be two-dimensional, which would make no sense, but rather an exact sphere that's locally flat. – Mike Scott Oct 7 '14 at 20:10
  • @MikeScott It would also have to be small and consistently dense to achieve flatness, rather than large. Im not convinced true flatness would occur though. – Gusdor Oct 8 '14 at 14:50
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    Why would it have to be small? The larger it is, the larger the radius, and the smaller the curvature. – Michael Campbell Oct 8 '14 at 21:18

I'll venture that the winner is none other than our old favourite; Krypton. 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.

Bronze-age Superman writer Elliott S Maggin (formerly Senior Writer for DC comics) described Krypton as a "failed star" and a "black-hole planet" whose mass was so great that conventional rockets wouldn't even allow you to leave the surface:

Jelassian had a habit of assigning nicknames like "The Big Rettubzzash," but pirates in general had an avuncular nickname for Krypton. It was "The Black-Hole Planet." Nothing ever left. It was as dense as a newborn star and as dark as the pit. 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. It was so heavy that space itself contracted around it. 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. The light radiated from every horizon. The days were barely brighter than Krypton's nights.

It took an enormous expense of energy to launch anything from the world's surface. 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. 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. He gave himself the chance to make the only test of his prototype starcraft.

If we're just looking at heavyworld sci-fi in general, then you can't got far wrong with Flux by Stephen Baxter. 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

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    The gravitational force inside the star would be less than on the surface, wouldn't it? – user14111 Oct 7 '14 at 20:13
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    @user14111 - Only assuming a perfect spherical object at rest. If it was spinning, the gravity a few milimeters below the surface would be slightly higher – Valorum Oct 7 '14 at 20:18
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    @user14111 don't forget the pressure – shadowtalker Oct 7 '14 at 21:52
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    The neutron star in Flux definitely was spinning. The vortexes formed in the neutron superfluid were a major plot point. – Ross Presser Oct 8 '14 at 4:53

I don't remember the name of the story; but you didn't ask that.

I believe that the answer might be Jupiter.  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.  Three of them traveled there in a non-airtight spaceship (rather than try to build something that could withstand the atmospheric pressure).  They encountered creatures that were sufficiently advanced that they attacked the robots with weapons (although not effectively).

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    On a related note, the hydrogues inhabit gas giants and the faeros inhabits stars in The Saga of Seven Suns. – Null Oct 7 '14 at 20:48
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    The title is "Victory Unintentional". There is a Wikipedia page for that story. – user14111 Oct 7 '14 at 21:13
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    Jupiter is also inhabited in Arthur C. Clarke's 2010: Odyssey Two, although it's pre-sapient life. – Ghillie Dhu Oct 8 '14 at 1:58
  • And by sapient life in Timothy Zhan's Manta's Gift – Sean Vieira Oct 8 '14 at 17:03
  • The question has been edited to exclude Jupiter. Planets with solid surfaces only. – Mike Scott Oct 9 '14 at 4:50

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. ;-)

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).

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".

The highest gravity planet to bear human life in the PR universe would be Oxtorne, a 4.8g world. A shipwrecked crew of emigrants managed, with the help of genetic engineering, to adapt to the harsh environment of their world within four generations.

  • +1 I remembered this age old issue but would for the life of me not have been able to remeber its name. :) – fgysin Oct 9 '14 at 7:33
  • I admit I cheated and looked it up on Perrypedia. Since I was pretty sure this was during the search for ES, I looked up the title list, and when my eyes fell on the title, I knew I had found just the one. ;-) That's also where I found the exact gravitation, I just remembered it was 900-ish. – DevSolar Oct 9 '14 at 7:37

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.

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. So they're not exactly life forms in high gravity, but maybe it still counts.

  • And not sure if it counts but I believe in one of Banks' novels there's a mention of a culture that "transcended" by moving their minds into a super-dense neutronium-type computer planet. Maybe the reference is in Matter? Or maybe Surface Detail. – Zan Lynx Oct 7 '14 at 22:43
  • @ZanLynx I don't remember that from the Culture novels but it sounds a lot like the Hades Matrix from Alastair Reynolds's Revelation Space series. – Robert Oct 8 '14 at 2:56
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    You know, I believe you are correct. Reynolds it is. – Zan Lynx Oct 8 '14 at 16:52

First Mesklin popped my mind from "Starlight" by Hal Clement. 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 so distorted that the strenght of the gravity on its equator is slightly different than on its poles.

  • Actually even Earth has gravity gradients on its surface, but that's probably not what you mean. ;-) – DevSolar Oct 8 '14 at 14:12
  • I think in the novel it was 2.5 times larger gravity on the poles. – mg30rg Oct 8 '14 at 14:21
  • 2.5 != "slightly different" ... – Torben Gundtofte-Bruun Oct 8 '14 at 20:09
  • A few misconceptions here. First, Hexanerax 2 is a planet and not a neutron star -- perhaps you're confused by my answer giving Hexanerax 2 also mentioning (to dismiss it as not a planet) the neutron star called Dragon's Egg. Second, Mesklin's variable gravity is not caused by its shape -- rather both its distorted shape and its variable gravity are caused by its extremely high rotation. Third, the gravity at Mesklin's poles is over two hundred times as strong as at the equator (660G versus 3G), not "slightly different". – Mike Scott Oct 9 '14 at 4:48
  • @MikeScott - You might be right. I have read "Statlight" when I was a kid. – mg30rg Oct 9 '14 at 7:43

recent: A Soldier's Duty by Jean Johnson. Protagonist, Ia, is from planet Sanctuary. It is a heavy world (defined as >1.5g) with a gravity of 3.28g.

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    3.28g is only a fraction of what was posted in previous answers. The question isn't looking for "what are all the heavy worlds". It's looking for the heaviest, so posting an answer that is lighter than existing answers is rather counter productive. – Beofett Oct 9 '14 at 12:48

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