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Could a superearth be hospitable (survivable?) for humans?

  1. Sep 23, 2012 #1
    Yes, I know, a civilization able to send a colony space ship on distance of many light years wouldn't probably be very sensitive to a harsh climate...

    Assumptions:
    - well within habitable zone;
    - there is some local life that was able to generate atmospheric oxygen;
    - you can pick a whichever place good place on its surface;
    - no cheating, no GMO humans; ;)
    - if any lucky but possible additional natural processes were needed please assume them but list them.

    With ex. 8 earth masses it should roughly (ignoring matters of density) it should have roughly twice earth gravity. Crushing, but not directly lethal for unprotected human.

    Do it have to be a water world? Would it have to have ultra dense atmosphere? (Could some lucky strike of a planet size object strip it of its volatiles, thus preventing appearance of water world with ultra dense atmosphere)

    How would look its plate tectonic? Would it be relatively flat because of gravity, or with such mass it would be so geologically active that mountainous landscape would anyway appear?
     
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  3. Sep 23, 2012 #2

    mfb

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    Do not expect that this life will produce anything edible. At the same time, do not expect that our immune system knows how to deal with any life there, so maybe humans just get eaten (cell by cell) by something similar to bacteria.

    Maybe, depends on the situation (especially the type of the star).

    Publish it, if you find a good answer ;).

    Gravity, atmospheric density, winds, rain (or similar), type of rock... all relevant for surface structures.
     
  4. Sep 23, 2012 #3

    Drakkith

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    What is a GMO human? Genetically modified? If so, why not? I personally expect this to be a requirement if we are going to colonize planets that already have life adapted to them.


    That's pretty high. Just breathing while lying down would probably take effort. At least at first. Perhaps the people would adapt and build up muscle to counteract it. Keep in mind that this is much worse than someone simply weighing twice as much here on Earth due to obesity. Imagine your head weighing twice as much as it does. It would probably give you severe neck issues. On Earth gravity is still 1g, so even if you are fat you can mitigate some of that extra weight by letting it rest on the ground or your chair or whatever. The only time you really support all of it is when you are standing.

    You know, I've never really thought much about immunity vs local organisms. I suppose its possible, if not probable, for either ourselves to be completely immune to practically everything on the planets, or extremely vulnerable to said organisms?
     
  5. Sep 23, 2012 #4
    Don't forget protein chirality. There's a 50-50 chance that nothing growing or living there can be digested or metabolized at all.
     
  6. Sep 24, 2012 #5

    mfb

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    If different types of chiral molecules are independent of each other, it might look different. However, we do not even know if other life uses proteins similar to ours at all.

    We have so many different types of bacteria on earth, digesting so many different things. I would expect to see some types which can digest human cells. Well, that is quite speculative with just one example of life on a planet.
     
  7. Sep 24, 2012 #6
    Oh, come on, local organic material can be converted before consumption to simple, easy to digest compounds like ethanol :biggrin:

    From practical reasons one can bring his own species, so chirality would hamper habitability seriously.

    Why not? Because it changes the question from "how could such planet look like?" to "what can we achieve with GMO?" Thus the proper subject would cease being "General astronomy" and the topic in such a case shall be moved to "Biology" or "Medical Sciences". Yes, realistically, the main reason why a civilization that goes on inrastellar travel is not GMO, is that's already dominated by AI that treat all carbon life forms as outdated model. ;)
     
  8. Sep 24, 2012 #7
    I wouldn't make this assumption. Having organisms living for years and years on such a vessel might make them more sensitive to a harsh climate than before they embarked on the journey, and maybe even sensitive to small variations in climate. To live in a regulated environment for years on end, where large, planet-like temperature fluctuations are rare could inevitably mitigate the colonists ability to adapt.
     
  9. Sep 24, 2012 #8
    It's a bit more than chirality. All multi-celluar life on the earth using a particular amino acid code, and it's likely that any life on another planet would use a different code. It might be possible to break things down, but it's not clear how fermentation would work or whether it would work at all.

    One other thing is that there are likely to be some interesting interactions between any bacteria you bring and any local organisms.

    It would be a subfield of astro-biology. Also one thing that becomes pretty quickly obvious is that it's easier to solve the problems of interstellar travel through biology rather than engineering. It's probably a lot easier to design a human body that can live for 600 years than it is to accelerate a starship to 0.9c.

    Then you get into some interesting politics. In the 1960's it was pretty obvious that humanity would colonize the stars because it was there. Right now, we are having problems even getting into low earth orbit.

    There's an interesting paradox. A lot of the motivation for getting off the planet was because we had two superpowers in a life and death struggle. Without this sort of struggle, no one is interested in getting off the planet. With that struggle, you end up risking total war that destroys the planet. So to get into space, you need just enough conflict to force people off the planet, but not so much that it destroys the planet.
     
  10. Sep 24, 2012 #9
    I'm still interested. The world is even less safe than it was in the Cold War and an extinction-level impact could always be right around the corner.
     
  11. Sep 24, 2012 #10

    Drakkith

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    How is the world LESS safe now? Without two superpowers primed to annihilate each other and most of the world it sure seems a whole lot safer to me.
     
  12. Sep 25, 2012 #11

    Ryan_m_b

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    Some initial thoughts:

    1) Twice Earth gravity is quite dangerous. It's analogous to walking around with a twin on your back. Any fall is going to have the potential for serious injury or death and I can't imagine the strain on the colonists joints and cardiovascular system. On top of that we have no idea what the long term health effects (especially during development) are for living out of Earth gravity. Astronauts spend a few months in freefall and have to fight of a plethora of problems, going from conception to adulthood is likely to be even more complicated.

    2) A planet that massive is likely to have a much thicker atmosphere which in turn would heat up the surface no?

    3) The chances of the local ecology being compatable are slim to nil. Bear in mind that we can't safely eat the majority (or close to I would argue) of organisms found on our own planet. We evolved to live in a very specific ecological niché, just because we've spread around the planet doesn't mean we can jump of it easily. Leaving aside matters of chirality it might not even opperate on the same fundamental biochemistry. On top of that even if the local ecology is close enough to be compatible with us then within minutes of stepping out the airlock a superantigen would probably kill everyone. If not that then some form of infection we have no immunity from.

    I'm sorry but space is not the New New World. You can't get there on the cheap with a brace of pioneers and hack out a society in the new fertile land.
     
  13. Sep 25, 2012 #12

    Chronos

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    It is unclear how biochemical processes might evolve under massive gravity. My guess is it would be different from earth. In fact, I doubt biochemical processes would evolve similar results to those on earth under identicaly initial conditions.
     
  14. Sep 25, 2012 #13

    mfb

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    Just thinking... if that is possible (and as you can see from post 2 and 5, I think it is), it might be a serious threat for humans on earth: someone could design such a thing.
    If it is completely different from life on earth, it might work the other way round, too - organisms on earth might digest it, and the species on earth (=the possible number of thing-digesting species) would outnumber the designed things by far.
     
  15. Sep 25, 2012 #14

    Ryan_m_b

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    True though there are enough deadly attributes in terrestrial organisms that very successful bioterrorism could simply stem from combing them (for example inserting NDM-1 into a plethora of deadly and contagious but currently treatable pathogens)
     
  16. Sep 29, 2012 #15
    Harmful - yes, immediately lethal - not. Actually there are people with my height and twice my mass who are alive and able to walk.

    Merely more effective greenhouse effect is not a problem, just the planet would have receive less energy from its star for everything to level out.

    I'm more afraid of high atmospheric pressure which, pending on composition means: oxygen poisoning/ carbon dioxide poisoning /nitrogen anaesthesia.

    I agree that the chance of edible local organism are low. On the other hand bringing your own plants and animals sounds as rather simple solution. Yes, presumably some of them might become invasive specie and cause local disaster. Concerning allergy (or oppositely lack of sufficient reaction of our immune system) - hard to say. I'm not specially afraid of contracting tobacco mosaic virus ;)

    So -rephrasing my question - is some kind of stripping of atmosphere and hydrosphere a realistic scenario for some superearths? (I think about collisions) Should the landscape be flattened by gravity or not so much? (I'm curious because it might be possible that the most friendly place could be mountain ranges)
     
  17. Sep 29, 2012 #16

    Ryan_m_b

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    I only have time for a quick post from my phone but regarding mass it isn't analogous to bigger people, your body adapts to your size as it changes but in this case the mass of everything is different. I question the ability to adapt to that. Also falling 1 metre is as dangerous as falling 2 on earth as everything will accelerate faster.

    Regarding bringing terrestrial organisms the complexity of biospheres is utterly non trivial. Throwing down some life in a world it is not adapting to is not going to give you a pop up biosphere.
     
  18. Sep 30, 2012 #17
    The gravity problem would be a non issue for the body to handle. The traveling space craft would just have to be put into a spin to simulate the gravity on the 'new' planet for the last 6 months of travel time to bulk up Arnie style! The crew would have to consume a calcium rich food source to increase bone density also.


    Damo
     
  19. Sep 30, 2012 #18

    Ryan_m_b

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    Living in 2g is not equivalent to carrying twice as much weight in 1g. If this thread is going to crassly ignore any biological considerations in favour of bold assertions then it will be locked.

    Let's start discussing the science properly people.
     
  20. Sep 30, 2012 #19
    But who asked for full bioshpere? Assuming that Earth plants are adapted well enough to survive and have no natural enemies - they look like potentially invasive specie. What would humans really need is few monocultures able to produce edible crops, nothing more.

    So far your crucial scientific argument here is that you have moderator privileges. You unquestionably have that, but that's argumentum ad baculum, which is only partially convincing, at best.

    I agree that trying to treat is 2g as carrying twice as much is indeed oversimplification, and if possible should be replaced with more nuanced approach. So your more nuanced idea is? (I can't think anything much better now but if you want to place some more useful input I'd grateful. So far you had an interesting point with objects falling quicker because of higher gravity)

    Concerning adaptation of joints, bones and muscles - do you consider that in that area "carrying double weight" would be so bad approximation? I mean for blood system that indeed might be trickier.

    The best that I could find was about mice that were able to reproduce at 2gs.
    http://www.time.com/time/magazine/article/0,9171,897495,00.html

    I'm also curious at how high gravity you'd put threshold for human adaptation limit.
     
    Last edited: Sep 30, 2012
  21. Sep 30, 2012 #20
    EDIT:
    I found something better:
    Source:
    http://jap.physiology.org/content/95/3/1266.full
     
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