Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Maximum Habitable G?

  1. Apr 25, 2007 #1
    Maximum Habitable G??

    Hi, read on the net about the detection of a 5 * Earth Mass planet today orbiting around Gliese 581, and this got me thinking about the titled question which I have been unable to answer for myself.

    What is the maximum 'g' (gravitational acceleration) that a human being can live at?

    I was thinking in the context of settling other worlds, by 'live' I think some reduction in quality of life at higher g would be acceptable ie. reduced lifespan, reduced walking distance etc. but the 'guinea pigs' would have to be able to live and colonise said planet. Oh also no fancy high-tech aid's to raise the figure, maybe with the possible exception of walking stick's, zimmerframes, and maybe the use of wheelchairs.

    Thanks!
     
  2. jcsd
  3. Apr 25, 2007 #2

    jim mcnamara

    User Avatar
    Science Advisor
    Gold Member

    Our entire physiology is adapted to our current gravitational acceleration on Earth.

    Lower G values cause things like bone demineralization. Higher G values put tremendous strain on the circulatory system, for example. The cardiac stress of living at 5G's would be really deleterious for an adult. --My opinion based on what I've read about human centrifuge experiments.

    Air density/pressure would also be another long term problem. Absorption of other gases into blood starts to occur at higher ambient air pressures. I guess we could assume 5 atmospheres, which is about like scuba diving at depths a lot greater than 66 feet (3 atmospheres) - the point where nitrogen narcosis starts to occur.

    Plus, assuming there are animal-like beings there, we would be paper-tissue-like beings compared with them. If they wanted to shred us, it's be no problem.
     
  4. Apr 27, 2007 #3

    Mk

    User Avatar

    Who says that? Why?
     
  5. Apr 27, 2007 #4

    jim mcnamara

    User Avatar
    Science Advisor
    Gold Member

    Mkl - have you ever been in high G? It's a lot harder to move effectively.
     
  6. Apr 27, 2007 #5
    Hi,
    thanks for the reply's,

    If the air toxicity is the first limiting factor without respiratory aids, does this mean 3g (equivalent to quoted 3 atmospheres?) is the most acceleration a person can live at?

    Otherwise does anybody know then at what surface acceleration nitrogen narcosis becomes a problem - I suppose for this question there are lots and lots of variables (ie. ratio of nitrogen in atmosphere) but if it makes it any easier, just assuming this planet were Earth with a stronger gravity and the same Earth atmosphere.

    Also by the way, though Gliese 581c is aprox 5 Earth mass its surface acceleration is apparently 2.2g according to a few post's I have seen on the net, 1 referenced here:
    http://www.astronomy.com/ASY/CS/forums/340277/ShowPost.aspx

    I am sure any developed unfriendly native fauna would have a physical advantage over us but perhaps potential colonists could avoid them, or use high yield weapons to deter them if neccesary.
     
  7. May 7, 2007 #6

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Gravitational acceleration has NO RELEVANCE to atmospheric pressure. On the moon there is 1/6 G but absolutely no air (not 1/6 atmospheric pressure).
     
  8. May 7, 2007 #7
    Well I was really interested in a number for maximum habitable g, 3 seemed reasonable at the time,

    Are you sure g doesnt affect surface pressure?, The moon has no atmosphere to begin with so it's a little unfair to suggest it wouldn't have 1/6 atm at the surface as there isn't any air to begin with, anyways.

    Assuming air is hard particles, then pressure is the force these particles exert on a suface right? If we assume the 'surface' is the surface of world X and pressure is then the force exerted on this surface (is this ok so far?)

    Say world x has 1 surface g, but we increase it's density (and only its density no other change at all, no more or less air, no different air composition etc) so that it now has 2 surface g.

    With the changed acceleration component on our particles towards the surface, doesnt that result in a greater density of particles/particle velocity (+interactions) towards the surface, and therefore (as the surface isn't going anywhere, assume its perfectly static and hard) greater 'pressure' on the surface??

    Hope that was a pretty logical question, am i right or way off track? :) and still want a value for maximim habitable g (assume Earth but greater density alone) :D
     
  9. May 7, 2007 #8

    chemisttree

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    Air pressure is the weight of the air column above the sensor. If there is more air there is more weight. Gravity alone says nothing about the amount of atmosphere of any given planet but acceleration due to gravity does determine how much weight (pressure) there will be for a given amount of atmosphere. A larger planet with a much thinner atmosphere than our own could have a pressure equal to that of earth's. An earth-sized planet with much more atmosphere than we have would have a higher pressure.
    Gravity alone cannot provide any information about pressure.

    The moon example was provided only to illustrate that there is missing information....
     
  10. May 23, 2007 #9
    Higher g values would put a stress on ones cardiovascular system, but that system can increase in strength. I doubt anyone knows what that limit is.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Maximum Habitable G?
  1. Sensitivity to G (Replies: 2)

Loading...