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

Gravitation on planets!

  1. Aug 6, 2010 #1
    I was wondering if the gravitation is too much on earth.
    What if on some other planets is less. How that affect life ?
  2. jcsd
  3. Aug 6, 2010 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    How could we possibly answer that question? We are just now finding planets outside of our solar system and have no evidence of life other than us. We have no real observations to base an answer on. You are asking a question that is more within the realm of science fiction then science fact. Since the only lifeforms we know about are those that exist on earth and have no evidence to base theories on any discussion on this must be speculative.

    As for low gravity, we have plenty of life in our oceans, is not that a low gravity environment? Feel free to use your imagination, just don't post your speculations here.
  4. Aug 6, 2010 #3
    Usually thinking about it, instead of making derisive, irrelevant, and close-minded comments.
    Clearly, because these boards, not to mention science as a whole are no place for "speculations," or "theories," we're only concerned with observational "facts." Just kidding! Oddly enough, most science is (or starts as) speculation and varyingly-wild guesses, you know, little things like heliocentricity, the standard dogma of molecular biology, genetics, relativity, cosmology... they're kinda cool.
    Now, to the actual question:
    There are lots of important things to consider with regards to lower-surface gravity planets, in the end statistics will dominate--you could hypothetically have any sort of life on any sort of planet--but we can speculate about certain trends. Here are a few thoughts I've cooked up in a few minutes:

    1) It would probably be harder for life to evolve on smaller (lower gravity) planets, due to weaker magnetic fields (which protect the surface from radiation), less-dense atmospheres (required for containing oxygen, water, methane, etc), and more chaotic thermal ranges (due to the above effects, in addition to less geothermal activity).

    2) If there was life, it could be bigger without requiring too much strength/energy. Biophysical analysis of skeletal mechanics shows that dinosaurs were really reaching the size-limit of what biologically-synthesized structures could support. Unless life on other planets found materials significantly stronger than bone (which is already really strong), they couldn't be much bigger with the same gravity; its logical to guess that with less gravity, they COULD be bigger.

    3) Due to less radiation protection, geothermal energy, and atmospheric confinement--sub-terrestrial (underground) life might work out a lot better.

    Just a few ideas. I hope I've encouraged some creative scientific thinking, and reinforced that we should always be asking questions, and thinking about new ideas however exotic they are!
  5. Aug 6, 2010 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    As mentioned in my first post life on earth initially evolved in the oceans, a low gravity environment.
  6. Aug 6, 2010 #5
    1) this isn't a place for wild speculations, life MIGHT have evolved in the oceans; but way to post many lines on why one shouldn't speculate about the question in the first place, followed by a single poorly thought out line trying to speculate about the answer--that makes a lot of sense.

    2) there is little reason to think that life in liquid water oceans on a large planet would be similar to that of small planets that--most planetary formation simulations show--can't have large liquid-water oceans.

    3) Buoyancy is quite different from low gravity, especially in terms of mechanics (and especially since buoyancy is proportional to the weight of water).
  7. Aug 6, 2010 #6


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You need to post some of the links you PM'd to me.

    Life starting in the oceans is speculation?? Thought that was pretty well accepted science.
  8. Aug 6, 2010 #7
    A fairly thorough (yet somewhat informal) discussion of prospectus of life elsewhere in the solarsystem (note saturn's moons especially) http://arxiv.org/abs/0908.0762

    The effects of higher-gravity (i.e. super-earths):
    Lisa Kaltenegger, James Kasting. Astrobiology. April 2008, 8(2): 394-396. doi:10.1089/ast.2008.1246

    Concerning geophysical requirements (haven't read this one, looks like a good review however):

    Origin of Life:

    I agree with oceanic origin of life, but that idea has only become popular fairly recently. Earlier it was believed to be in small ponds of surface water or hotsprings-type environments (this is largely due to the simplicity of pond-scum organisms, and the lack of knowledge of extremophiles at the time). *An irrelevant, but interesting aside: some ancient greeks thought fossils (e.g. of whales) were from abiogenesis spontaneously occurring underground, and just being unfortunately misplaced*
    Exogenesis is gaining a large following, althought it largely avoids the question, see for instance:
    The astrobiological case for our cosmic ancestry
    Chandra Wickramasinghe
    International Journal of Astrobiology , Volume 9 , Issue 02 , Apr 2010 , pp 119-129
    doi: 10.1017/S1473550409990413

    I've yet to see a good review article on panspermia, but they think abiogenesis will occur just about anywhere (relatively at least).
  9. Aug 6, 2010 #8


    User Avatar
    Science Advisor
    Gold Member
    2017 Award

    Last edited by a moderator: Apr 25, 2017
  10. Aug 7, 2010 #9


    User Avatar
    Science Advisor
    Gold Member

    Undersea environments combined with volcanic activity are prime breeding grounds for abiogenesis. The chemicals are all there in abundance and there is sufficient energy to foster constant molecular activity. Self replicating molecules will inevitably arise under such conditions given enough time, IMO, and these environments tend to persist over vast periods of time.
    Last edited: Aug 7, 2010
  11. Aug 8, 2010 #10
    The portion concerning the carbon-silica cycle was pretty convincing. I'm mostly with Integral here, in that it's almost an impossible question to answer... good article though.
    Last edited by a moderator: Apr 25, 2017
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook