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You go to sleep one day, and wake up on a different planet. Let's say the atmosphere of this planet has about the same composition as on Earth. Actually, this planet has pretty much all of the same physical properties as Earth. However, this planet has $4.5\ M_\oplus$ (Earth mass), and $1.8\ R_\oplus$ (equatorial radius of Earth), and as such, the acceleration due to gravity has increased to $1.4\ g$.

Obviously, the local flora and fauna has evolved to survive in these conditions. My question is two-part:

  1. How does this change in gravity generally affect the atmospheric pressure at the surface of this planet? I say generally, because I understand that there are probably other complicated factors to consider when figuring out atmospheric pressure, but I've had a hard time finding a general equation to figure out just how a change in gravity would change atmospheric pressure. Is it just a 1:1 increase?
  2. How would you feel waking up on this planet? That is, what effects would the increase in gravity/atmospheric pressure be on your body, and without any mechanisms or devices to help you adapt, how long would it take (or would you be able) to adjust to these new conditions?

(There are likely other physical properties of this planet that are different due to the increase in mass/radius, however, at this point I'm only interested in the effects of acceleration due to gravity and atmospheric pressure. But if you can think of other properties of this planet that would present an immediate physiological challenge in this scenario, feel free to comment!)

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Air pressure would be 1.4 times more, or less than half as much, depending on which other characteristics match for Earth. The increased gravity wouldn't be an issue.

The air

Air pressure is just the mass of the air above you. Hold out your hand, look at a square inch on your palm. Now imagine a square column rising from your palm straight up into space. There are about 14.7 pounds of air contained in that column. On a planet with 1.4g that air would weigh 1.4 times heavier, so the air pressure would be 1.4 times more.

However, if you've actually just transplanted the exact same amount of air from Earth, things will be quite different. The surface area of this new planet is much larger, so the same air wouldn't quite stack up the same way, literally. It would be far more spread out. The increased gravity doesn't offset the difference and you'd end up with about 6.35 psi, less than half that of Earth, so you wouldn't be waking up at all.

Finding a mix between the two would give you identical air pressure. Though the composition would likely realistically be different. It would hold onto more low mass gasses and would have collected more in the first place.

The gravity

This article says:

According to NASA’s Ames Research Center’s expert on humans in space, a person has survived 2x Earth’s gravity for 24 straight hours without ill effects. They go on to claim that it is theoretically possible for a human to adapt to a gravity environment that is between 2x and 3x that of the Earth. However, they say that at 4 times Earth’s gravity (4G) or above, human physiology cannot maintain sufficient blood-flow to the brain.

If true, then the 1.4g wouldn't be very deleterious to a human waking up there. They will get tired a little more quickly, but will likely adapt eventually. I've not experienced it, but I imagine this would feel like carrying around evenly distributed weights on your body. Weights adding up to 40% your body mass. Just being a highly adaptable human would be all the tools required.

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  • $\begingroup$ An accurate calculation of air pressure for transplanting the earth's on the first answer +1. It would be nice to explore the expected resulting air pressure and mix for being a superearth. However, since 78% of atmo is nitrogen and this is considered mostly volcanic outgassing, the total nitrogen would likely also be proportional to surface area. The total oxygen, again would likely be proportional to total area for similar reasons. With these adjustments, expected pressure would be 1.4 times earth pressure. $\endgroup$
    – Gary Walker
    Commented May 1, 2015 at 20:41
  • $\begingroup$ Higher gravity would also decrease atmosphere loss to space, so a slightly high overall pressure. Helium and hydrogen are the only significant loss and free hydrogen tends to become water anyway, so mostly a bit more helium. $\endgroup$
    – Gary Walker
    Commented May 1, 2015 at 20:45
  • $\begingroup$ @GaryWalker Yep, I said "It would hold onto more low mass gasses and would have collected more in the first place." $\endgroup$
    – Samuel
    Commented May 1, 2015 at 20:47
  • $\begingroup$ Yes, you did -- I just added a little to the expected result. Still plenty of room for variability, much less effects that were not considered. $\endgroup$
    – Gary Walker
    Commented May 1, 2015 at 21:05
  • $\begingroup$ Most healthy people can train for a marathon in under a year. I imagine adaptation for most healthy people to 1.4g will occur similarly quickly. You may not feel comfortable but you could live your normal life. $\endgroup$
    – Jim2B
    Commented May 1, 2015 at 21:08
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I am neither a physician nor a physicist, but I have some guesses.

  • Walking around unencumbered would have about the same feeling as if you distributed 40% of your base mass around on your body as additional mass (i.e. if you weigh 100 kilos on Earth, and you pick up a 40 kilo wet blanket and make a poncho out of it). You'll tire easily unless you're in amazing cardiovascular shape. However...

  • Atmospheric pressure will be increased significantly (not sure how much, presume linearly, which is wrong), and you'd have 40% more oxygen by volume with each intake of breath, so your endurance hit would be offset some, though I can't say by how much.

  • Walking uphill would be very difficult.

  • Walking downhill would be easier.

  • Regular (daily, often) physical activity for 6 months or a year (presuming the same year length) should put the body into a condition where it's "used to" the increased gravity.

I his Mars Trilogy, Kim Stanley Robinson described one of the main characters, born on Mars, going to Earth. He tried to prepare along the way by exercising, etc. But the impact of the thick air, bright sun, and the excessive gravity was beyond what he was prepared for. It was a well-reasoned description, at least from this reader's perspective. You should try to find that passage and review it. It's been years since I read it, so can't give you more, but it's there.

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