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I've been told that having a thicker atmosphere would make it easier to fly, particularly of heavier-than-air designs, so I'm interested in giving my planet such conditions. I'm mainly interested things like temperature, weather, seasons, the distribution of land versus water - basically, how the planet itself would be affected simply by having a thicker atmosphere. I'd still like for this planet to be Earth-like, capable of housing multiple intelligent humanoid species.

I'm admittedly not very knowledgeable about the subject, but I'd presume a few things - feel free to correct me if I'm wrong:

  • Wind: Winds would be more forceful... I think? This one I'm less sure of!
  • The planet would be hotter on average, since less gas would escape the atmosphere
  • Objects could be treated as lighter than they are - people jumping higher, objects thrown farther, heavier things more capable of flight

Are these assumptions wrong? And what other possibilities/realities are likely from such a scenario?

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  • $\begingroup$ Your second bullet. Gas escaping the atmosphere and heat loss are two different things. Did you mean "heat escaping the atmosphere"? $\endgroup$ – Adrian Colomitchi Mar 10 at 22:27
  • $\begingroup$ I both did and didn't mean that! In my ignorance, I (wrongfully?) assumed gas equals heat (and thus less gas escaping equals more heat on the surface) for the purposes of the greenhouse effect. I should've said radiation, I think? Like I said, not very knowledgeable... $\endgroup$ – Vigilant Mar 10 at 22:34
  • $\begingroup$ Radiation, yes. Mainly IR matters most for cooling. $\endgroup$ – Adrian Colomitchi Mar 10 at 22:36
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    $\begingroup$ Objects could be treated as lighter than they are - people jumping higher No. Physics won't make you effectively lighter in your atmosphere. Objects won't travel further either - in general atmospheric drag will hit harder in a denser atmosphere which is likely at ground level with a thicker atmosphere (i.e. a higher ceiling). $\endgroup$ – StephenG Mar 11 at 0:25
  • $\begingroup$ @StephenG, are you sure about that? Astronauts use a special "atmosphere" (one which is much, much denser) for weightlessness training. While it's not exactly the same as actual microgravity, claiming it has no "effective lightening" effect doesn't seem right. (Granted, the effect in breathable atmosphere may be negligible, and of course the point about drag is spot-on.) $\endgroup$ – Matthew Mar 11 at 15:19
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I will assume you mean more massive atmosphere where you means more thicker.

A hot atmosphere will be more thicker than a cold one, both with same mass. The cold one, although, will be denser.

Winds will be more powerful, yes. But in ground layers its will be slower. For instance, Mars winds reach 60km/h and its like a smooth breeze. Venus winds in surface are max 1m/s (3,6 km/h), while reach astonishing 140m/s (504 km/h) at 70 km altitude.

You are correct about temperature too: atmosphere molecules will trap heat anyway, some less, some more, and the denser is your atmosphere, the more heat will be trapped. Winds will spread the heat evenly.

As @StephenG commented, no, what will make you and anything else feel lighter is the gravitational acceleration.

A denser atmosphere will erode faster the geological features. A planet with low or none of things like montains, canyons or other hard formations. Impact craters or tectonic activity will scar the surface for short times.

A high rate of oxygen will allow insect-like and any other epidermal breathing live growing bigger. Otherwise, it will also be favorable to start fires.

Land/water rate is not related with atmosphere, but a denser atmosphere probably come with more volatile compounds. Being Earth-like in other parameters, this world will be rich in organic things, beside water, and still more favorable to life than Earth really is.

Climate, after all, with strong winds and no major features acting as barriers, uniform and hot temperatures, will extend tropical zone some kilometers far from equator and pull the temperate zone inside the polar zones.

Maybe in the fiction the planet looks more like Dagobah

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