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Consequences of denser atmosphere on Earth-like planet

  1. Feb 26, 2015 #1
    I made a brain storming, but hope that someone would be able to point out what I may have missed out. Assumptions - atmospheric pressure is 3 atm, but molar concentration of oxygen is comparable to earth. The rest is mostly nitrogen.
    (there are a few more assumptions like tidal lock, a bit lower gravity or a bit higher CO2 concentrations, but rather skip them for now)


    1) changes in the air transport, that were mostly discussed in the following topic:

    2) Vehicles would really have to be aerodynamic and better slow because of heavy drag (unless there is some good reason to burn fuel more generously). Do I get correctly that a car designed for Earth would for the same speed use 3 times more fuel, while the same fuel efficiency would get while driving [Earth speed]/[sqroot(3)]?

    3) Water boils in something like 126C degrees.

    4) Maximum range of guns - divide by 3 (?), effective presumably not as much reduced because that part of effective gun range is defined by aiming problems, which would not be affected.

    5) More native, airborne creatures. Earth chicken would turn in to a formidable flier. ;) (any design including insect like, flying fish like)

    6) Milder climate than otherwise because of heat retention and better distribution.

    7) Winds with greater force (so boost for any sail ships). But shouldn't the speed actually go down?

    (Any other ideas? Suggestions?)
  2. jcsd
  3. Feb 26, 2015 #2


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    The higher concentration of "inert" gas (N2) is going to reduce flame/combustion temperatures significantly; no forest fires at all, no yule logs, "discovery" of fire by indigenous species is going involve pine pitch/tar and hot volcanic rocks, or something similar with higher energy fuels than wood or other cellulose.
  4. Feb 27, 2015 #3
    Shouldn't it just matter the partial pressure of O2?

  5. Feb 27, 2015 #4


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    Same heats of combustion, two extra atmospheres of nitrogen along for the ride that contribute to the heat capacity of the combustion products, cutting the temperature rise to ~ 1/3 of what it is here on earth. i.e., man (or whatever dominant species arises on the planet) will never independently discover fire, develop a metallurgy beyond beating artifacts from native copper and gold, or fire brick or ceramic artifacts.
  6. Feb 28, 2015 #5
    Good point. Thanks!
  7. Mar 2, 2015 #6
    So by the same mechanism, also loosing more heat in cold climate for breathing, right?
  8. Mar 2, 2015 #7


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    Hadn't even thought of that, but, yes --- extra load on sinuses and cardio-vascular system pre-heating/heating air in cold climates, and a lot of extra heat input in Death Valley, if that extreme of heat is available. Good catch.
  9. Mar 13, 2015 #8
    I have one more idea: different hail/ice pellets:
    -the denser atmosphere should actually be able to keep longer those balls of ice in air, thus making them bigger
    -denser air means lower terminal velocity, so the damage would not be so awful

    EDIT: lower terminal velocity of for example human like being, but I don't see many likely scenarios where it might matter, except maybe using smaller parachute.
    Last edited: Mar 13, 2015
  10. Jul 15, 2015 #9
    Two more consequences:

    1) Slower evaporation
    2) Guns would transfer less energy to bullets - the gasses produced by gunpowder explosion would reach the ambient pressure quicker.

    (In both cases I have no idea how to calculate that)
  11. Jul 15, 2015 #10


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    Evaporation rates? Mean free paths will be shorter, so, yes. However, I suspect you're thinking more about boiling points being at higher temperatures?
    Not noticeably. Chamber pressures in firearms range from ~1000 to ~10,000 atmospheres. There will be a reduction in effective ranges of projectiles due to the denser medium.
    Look for "ballistic coefficient, trajectory, sectional density." Should get you started.
  12. Jul 15, 2015 #11
    This part I figured out a while ago (first post, point 3 ;) ). However, I later started to wonder whether it would affect evaporation rate under lower temperatures.

    Thanks, I'd google that later after I have some sleep.
  13. Jul 15, 2015 #12


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    o:)o:)o:) Maybe I'd do better with a nap myself.
  14. Jul 16, 2015 #13
    After a nap:

    From drag formula:

    So any Earth bullets would only have 1/3 of range. To combat that... Damn, a square root, so would have to have 9 times more energy... Running with anti-tank rifles is not practical ;)

    So realistically - more powder, heavier bullet and accepting much shorter range?
  15. Jul 16, 2015 #14
    Sound would travel much further.

    Astronomical sciences would suffer, the dense atmosphere would obscure the stars more.

    You mentioned insects, be careful, even if Earth's atmosphere was three times denser, insects would not get any bigger. They absorb O2 through their skin so because volume increases faster than surface area, an insect's size is a factor of concentration of oxygen, not atmospheric pressure. Large flying creatures will need lungs.

    One of the first technologies humans discovered was pneumatics, if our atmosphere had been thicker, we probably would have relied on it heavily in the early days of civilization.
    Last edited: Jul 16, 2015
  16. Jul 16, 2015 #15


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    Or, longer bullets for higher (cross-) sectional density, faster spins for stability of the longer bullets, and still have to accept shorter effective range due to larger drift of projectiles in cross-wind conditions. "Exterior ballistics, tractability of spin-stabilized projectiles."
  17. Jul 16, 2015 #16

    Only a little. The real hit would in this particular case come from tidal lock :D

    good point, but I meant that under such conditions it requires less effort to become an airborne creature.

    May you explain how would it help?

    So in other words:
    Ok... that would be excessive... :D
    More realistically something in line of:

    For practical purposes it seems there would be a tendency to use guns which would have in case of close combat impressive piercing capability, but limited stopping power. It would also reduce advantages of bullet proof vest in any close combat.
  18. Sep 2, 2015 #17
    Bike paths wouldn't be built with high slopes or narrow turns :D
    Recumbent bicycles are much more aerodynamic. On our planet they finally turned out to be unpopular. They've got their drawbacks concerning lower manevurability and lack of possibility to ride uphill standing. Presumably on such planet their shape would be more practicall and infrastructure would be designed to match their needs.
  19. Sep 4, 2015 #18
    I wondered about the floating skateboard from Back to Future 2, would it be easier to make it with denser atmosphere?
  20. Sep 15, 2015 #19
    I just thought about this while watching a storm last night. Coastal life will likely be a little more robust than on earth. The denser atmosphere will make more violent storms and much larger storm surges. Storms are low pressure areas, which produce a noticeable bulge in the ocean. It's mostly only noticeable on Earth during a hurricane, but if the atmosphere was denser, coastal storms would be far more devastating. I remember the last hurricane we had here in New Jersey, the storm surge hit at the same time as high tide and caused a lot more damage than it would have otherwise.
  21. Sep 15, 2015 #20
    More robust? So for example coastal species of trees that are lower / more flexible and don't break so easily?

    Impact on any civilization:
    -more risky sea travel, higher importance of robust ships / good weather report?
    -impact on settlement? Would it mean that coastal areas would be actually repelling settlements, in contrast to areas at least a few hundred kilometres inland? Or just following Bible would be enough (building house on a rock + city on a hill :D )?
  22. Sep 15, 2015 #21


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    Dust and fog will stay suspended longer and reach larger particle sizes, so visibility will be lower.
    Bigger contrast between blue noon sky and red sunset.
    Somewhat easier to survive a long fall due to lower terminal velocity.
    Airships can be significantly smaller. Could biological airships ever evolve?
  23. Sep 16, 2015 #22
    Yeah, coastal species would probably have very strong trunks and deep root systems. The root systems would have to be able to hold onto soil, the immense storm surges would cause erosion. An Earth hurricane can wipe a beach away completely.

    I don't think it'd affect settlements that much, humans have always settled flood zones, it actually helped our civilization. The Egyptians taught themselves geometry because every year their settlements would flood and the path of the nile would change slightly. I think people will still settle those areas, but they will either build much sturdier buildings, or less study buildings designed to last only one season.
  24. Sep 18, 2015 #23
    I do not have any idea how it should operate, thus don't know whether higher pressure would help it.

    Thanks for the fog / dust thing.
    I discussed (ok... quarrelled about airships) on different topic on this forum. I have low hopes about biological ones. However, I thought about other different creature... flying fish... which under such conditions was able to evolve in to an avian creature... and later make hops between lakes... to finally evolve in some remote lakes a specie of flightless flying fish...

    Settled flood zones, not because of suicidal tendencies but as alluvial valleys are so good soils. ;)

    May be useful for my story. (mentioning that they learnt about hurricane in the hard way, as some back story...) But I wonder whether it is not a bit US specific risk. I mean:
    - happens only in some hot climate, I do not have them in my country.
    - American preference for cardboa.... hmm... wooden houses.
    - Gov policy of encouragement of construction in danger zones (through capping insurance premiums).

    (but of course heavy storm would be more devastating than on Earth, if hit buildings of the same quality. That would be useful)
  25. Sep 18, 2015 #24


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    Call it what it is.
    Don't need tropical climate for heavy storms (northeasters), and it won't take large bodies of water (long wind fetch) to pile up monstrous waves.
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