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What planetary parameters such as plate tectonics and volcanism etc would best encourage the most uneven planetary surface on an earth like planet?

I want a world to be covered in very uneven terrain, the more precipitous the better over 90% of its surface whilst still providing a good place for humans to live or at least without it becoming uninhabitable for humans. How might this realistically come about? The world must be approximately earth-like, but planetary parameters can be changed within these bounds if it helps.

The planet may have seas but these should be broken up and dispersed and covered with mountainous islands.

The best answer will have the most uneven terrain over the greatest proportion of the planet.

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  • $\begingroup$ define level of habitability, humans vs extremophiles $\endgroup$
    – anon
    Oct 9, 2017 at 16:15
  • $\begingroup$ Must be habitable by humans. I will edit the question to make this clear. $\endgroup$
    – Slarty
    Oct 9, 2017 at 16:25
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    $\begingroup$ When you say, "habitable by humans", do you mean, they can walk around in ordinary clothes, breathe the air, grow crops? $\endgroup$
    – bgvaughan
    Oct 9, 2017 at 17:17
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    $\begingroup$ @bgvaughan yes. $\endgroup$
    – Slarty
    Oct 9, 2017 at 17:28

5 Answers 5

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Continental plates are the way to go... On Earth we have a bunch of small plates, and 7 big ones. As they spin and bump against each other, mountains are pushed up as the edge of one plate slides under another. The mightiest mountains we know -- the Himalayas -- are caused by India smashing into Asia.

So...

You need smaller continental plates, so that collision-born mountains will be more prevalent and you don't get all those tedious steppes and praries that you find in large continental interiors.

Per this interesting article (https://www.huffingtonpost.com/2014/04/07/earth-tectonic-plates-new-model_n_5104087.html) plates were caused by low-pressure areas underneath big plates, which caused ruptures. We need more of that. Perhaps kick up the core temp and magma flux a little bit, enough to create more fracture points, and voila! More plates.

The extra action will cause more volcanoes etc, but you're the boss of this planet and you can mitigate the problem. Perhaps sulfur-eating organisms remove extra minerals from the atmosphere. Perhaps people/animals just sigh and deal with it.

Now I can't guarantee no large continental areas, but we can cheat. Push the big ones up to the poles where they'll be useless. And then the rest of the planet can be small craggy continents and archipelagos.

Enjoy!

Update: This world will have more earthquakes on average than our world. I expect the local people to be a little fatalistic about this, in a "Man proposes, God disposes" sort of way. They'll probably steal a page from the Incas, who were extraordinarily good at making earthquake-resistant structures. See here: https://www.ancient.eu/Inca_Architecture/ . Thanks to Michael K for drawing my attention to this!

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    $\begingroup$ I like that this answer sounds like a cooking recipe =P $\endgroup$
    – Chiri Vulpes
    Oct 9, 2017 at 18:15
  • $\begingroup$ One aspect of our plate movement is that caused by the gravitational pull from the moon. A planet with many tectonic plates and one or more large moons might experience more plate movement than our own. However, if such a planet also had seas, then the tides would be larger, which would more rapidly erode coastlines making them more flat (and eventually sandy). Maybe then, no moons, but a far more unstable core would help move plates, eject lava etc. $\endgroup$
    – Ralph Bolton
    Oct 9, 2017 at 21:02
  • $\begingroup$ @RalphBolton I think you're right that a hotter core (maybe more radioactives!) would be safer in terms of getting the jaggiest planet. That said, two moons for a planet is inherently awesome, so OP might consider that at the expense of a little sand around the margins of his craggy continents. $\endgroup$
    – akaioi
    Oct 10, 2017 at 2:28
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    $\begingroup$ If you could somehow make the barysphere (the basalt crust) have less shear strength and be more "crumbly" than here on Earth, the tectonic plates would be smaller. Earthquakes would be more common, but the worst ones would not be as severe as ours. - This would require a different chemical composition of the crust but you don't have to explain, or even know, the details of that chemistry. $\endgroup$
    – A. I. Breveleri
    Oct 10, 2017 at 4:13
  • $\begingroup$ @A.I.Breveleri this is a great idea. If you look here: (jsg.utexas.edu/tyzhu/files/Some-Useful-Numbers.pdf) you'll find shear strength of granite is slightly less than that of basalt (14-50 vs 20-60 MPa). That might help. If you want way more info on this, here's a detailed report on testing rocks to failure: dtic.mil/dtic/tr/fulltext/u2/684358.pdf $\endgroup$
    – akaioi
    Oct 10, 2017 at 4:28
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Habitability is a very variable equation

so first to answer your question, probably a volcanically active planet like IO whose core is constantly squashed by the other moons and Jupiter. That would keep the crust from solidifying too much.

After that we need to create conditions where water is liquid and the atmosphere is breathable (for human habitability).

Then the question becomes what to do with that heat and volcanic atmosphere.

Like IO, put it far out in the solar system so the surface can cool faster. So the equation becomes a balance of supplementing solar heat for volcanic such that the average temperature supports liquid water.

And the atmosphere

Being a volcanic world the atmosphere wouldn't be good for photosynthetic organisms. However, plenty of terrestrial organisms are capable of making energy from volcanic environments. All humans need to survive is Air, food, and water. This is the crazy part. What if we would genetically engineer an algae capable of producing oxygen from volcanic energy. What if we could then reengineer our crops to produce edible foods from volcanic energy.

The final variable for human habitability is having a crust stable enough to produce long-term structures. This is largely an engineering problem however they would have to identify plates and build settlements towards the center as the edges would be too chaotic. These edge areas would probably be ideal for agricultural areas though as they would have more farmable energy.

This wouldn't be a lovely place for humans(as we know them) with the ash requiring masks but we could irk out an existence. With some self genetic engineering we could be adapted to thrive though.

This answer does rely a bit on the magic of genetic engineering but realistically, that's the answer to any real terraforming attempt.

Note: the engineered algae isn't too farfetched, algae was among the first organisms to survive the harsh early volcanic Earth so much so that it eventually changed the atmosphere. The only challenge here is making an algae capable of making oxygen from volcanic energy instead of sunlight. This would also be a great way to extract the harmful gases from the atmosphere as food sources for your air makers. Like our own ecosystem its likely you would need a spectrum of organisms to cleanse different toxins.

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  • $\begingroup$ "producing oxygen from volcanic energy" is easy. Hard part is: what chemical oxygen comes from? If it's from rock, it will also constantly sink into rock, making oxygen ritch atmosphere hard to obtain. $\endgroup$
    – Mołot
    Oct 9, 2017 at 17:16
  • $\begingroup$ The atmosphere would still have plenty of CO2 that can be converted to 02, $\endgroup$
    – anon
    Oct 9, 2017 at 17:57
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You may want low gravity so that your planet will have higher mountains and steeper ridges.

To avoid excessive erosion you may want also a thinner atmosphere.

Keep things "interesting" periodically going through a large meteor shower beautifying your world with brand new craters.

Thinner atmosphere would minimize "meteoric winter" effects.

You can even have a "no axial tilt" planet with a "cold season" right after the meteor shower.

Of course planet must be relatively young, otherwise it would already have weeded out the meteor swarm, unless there's a constant supply.

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A highly active hot planet with a very high proportion of light elements and their associated minerals. Basically the world is covered in a thick layer of what on earth is continental rock but coming up through this thick crust you have hot-spot volcanoes everywhere. No oceans per se but deep cold lakes between volcanic ridges and richly soiled steep mountainsides that can be terraced and farmed between the eruptions and landslides.

On the nasty side of life the air will be a little acidic and a little toxic due to excessive sulfur and associated compounds and you'll never know ahead of testing it whether that lovely clear lake is H2O or H2SO4. It rains acid on occasion and there's not much in the way of flat land that you don't make for yourself either, but it's livable.

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  • $\begingroup$ Why would a thick layer of continental rock be necessary? $\endgroup$
    – Slarty
    Oct 9, 2017 at 18:36
  • $\begingroup$ @Slarty Prevents plate tectonics that would otherwise concentrate upwellings into chains and belts that would decrease average uneven-ness by have flat ocean basins and wide continental blocs. Instead of mountains at the edge of flat areas you get a pincushion of volcanoes all over the surface in an even (on average) but irregular (in detail) distribution. $\endgroup$
    – Ash
    Oct 10, 2017 at 10:25
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Lower the viscosity of the mantle - that will do it one fell swoop. As @akaioi has elegantly answered, you need lots more continental plates, and you want them moving around a lot. It may cause quite a bit of vulcanism - but hey that's cool, right? You've got loads of extremophilic flora and fauna..

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  • $\begingroup$ Why does a lower viscosity for the mantle help? $\endgroup$
    – Slarty
    Oct 9, 2017 at 18:46
  • $\begingroup$ Lower viscosity means higher mean fluid velocity (that is, the stuff can move faster overall). That leads to more and more rapid drift of the plates floating on top. $\endgroup$
    – Nij
    Oct 9, 2017 at 21:48

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