B Goldilocks zones of other parameters

[Suppaman]

I understand the goldilocks zone but would like to know if there are similar limits with respect to supporting life as we know it for a planets gravitational force (min/max) and atmosphere pressure (min/max.) I understand gravity can affect pressure but so can the amount of atmosphere and do not know what limits that.

 

[mfb]

We don't know much about this, apart from the limits that feed back to the presence of water:
- The gravitational force cannot be too low, otherwise water (and the atmosphere) escapes to space. The limit depends on various things, but Mars is at the lower end of what can keep an atmosphere.
- The gravitational force can be high: Beetles from Earth can survive more than 1000 g for 2 minutes (study), they shouldn't have a problem under 10 g for a lifetime - and they are not even adapted to it. A large gravitational force typically leads to gas giants, however, and then you don't get liquid water any more.
- Low gas pressure: There are speculations that Jupiter's moons could have life under an ice crust. The moons don't have any relevant atmosphere.
- High gas pressure: See gas giants.

 

[Suppaman]

You mention extremes of gravity and gas pressure but I was thinking in a more friendly range. up to 4-6 G or an atmospheric pressure of 4 to 6 times more or at a level of 15k feet equivalent. Changes different enough to make life interesting, not impossible.

 

[mfb]

Well, we have many animals that can survive 4-6 g easily, and we have animals living at 4-6 times the atmospheric pressure in lakes and oceans. We also have bacteria living quite high up in the atmosphere. That part is no problem.

 

[Suppaman]

Living in water not the same. Do we have people living in such atmosphere conditions? It would be possible to simulate. I am sure real world things may have issues. And what is the likelihood of such planets? Developments in technology might have taken many different paths. The strength of materials and strength of the bones in a living being. If we ever go to the stars we might find many places that are a little bit different. xD

 

[jim mcnamara]

Scuba diving uses pressurized air*. Humans live in the Andes at 10000 feet elevation, due to changes in physiology - very high hematocrit, for example. Humans who come from lower elevations may adapt hematocrit but generally not to levels found in indigenous populations.

We do not have examples of life at higher G, so there is no good answer to that. High G force from acceleration during sharp turns in fighter jets causes unconsciousness, so we have an idea of limits of what people can endure on short time scales. There are also studies done on pilots as test subjects in centrifuges.

Here is a start: https://www.ncbi.nlm.nih.gov/pubmed/11542364

*can lead to the "bends" when decompressing from deep dives.

 

[Suppaman]

Yes, all this involves putting current people under such conditions. I am addressing what results we might have if we had 4 Billion years of evolution under such conditions. High G is not new, just read the SF story Mission of Gravity. But I am thinking of what limits we might encounter if we evolved into it. What science would limit life's possibilities? And exclusive of gravity, how much more air could you have without higher gravity? Is there some science that predicts the amount of air based on gravity?

 

[mfb]

We don't have natural places with several times the sea level pressure as gas pressure, but as humans can survive this for longer times, it is clear that life can handle these conditions easily. High pressure corresponds to high density - it would probably make flight more prevalent.

And exclusive of gravity, how much more air could you have without higher gravity?

There is no real upper limit, apart from gases becoming supercritical at some point. See Venus with its very high pressure. The atmosphere above you doesn't influence the gravitational acceleration anyway. A very thick atmosphere can heat the planet a lot.

 

[rootone]

The only life we know does require water in liquid form as solute for carbon and other elements.

 

[Suppaman]

As I often find when I ask a question I am actually trying to learn enough to ask a better question. So, to recap: The Goldilocks Zone refers to the habitable zone around a star where the temperature is just right - not too hot and not too cold - for liquid water to exist on a planet. I understand this concept. However, there seem to be two other parameters that are significant. The surface gravity and the atmospheric pressure at the surface. Both of these may be very significant should an Earth colony ship find a candidate planet but not so significant if one considers life evolving over billions of years. Given that such planets use the same building blocks, whatever is available from the periodic table, the significant constraints may be how extremes in these two parameters may be limited by chemistry and strength of materials.
This brings to mind some interesting situations. (1) What are the Goldilocks limits for human habitation (all else being most acceptable) for atmosphere surface pressure and gravity? Limits that colonists would use when deciding to move on or stay. (2) What are the interesting attributes for civilizations that evolved under much wider ranges of for atmosphere surface pressure and gravity? How might these have changed how a civilization might achieve technology advances we consider necessary to get off the planet? In all of our SF stories we never seem to encounter aliens who are comfortable with 10 G and 50 Bar atmosphere. I know it is speculation but what percentage of the Goldilocks planets are actually too far outside acceptable limits in these parameters for humans to be interested?

 

[mfb]

(1) What are the Goldilocks limits for human habitation (all else being most acceptable) for atmosphere surface pressure and gravity?

There are no long-term experiments outside the range Earth provides naturally.
In terms of atmospheric pressure, we know living at ~60% to 100% sea-level pressure with 21% oxygen and 78% nitrogen is fine. Lower pressure with higher oxygen content seems to be fine for a while as well, higher pressure with lower oxygen content is fine at least for weeks. The important point doesn’t seem to be the overall pressure, but the partial pressures. Oxygen cannot be too low or too high, nitrogen cannot be too high, and gases like CO2 or other toxic components have quite strict upper limits.
To reduce g-forces for more than a few minutes you have to go to space. We had astronauts living in space for more than a year, but we have no idea if reproduction and growing up works under these conditions, and if not, how much gravity is needed for that.
To increase g-forces for more than a few minutes you need a centrifuge. I’m not aware of long-term experiments (more than a day) in centrifuges, and I’m quite sure no one tested human reproduction and children growing up there.

(2) What are the interesting attributes for civilizations that evolved under much wider ranges of for atmosphere surface pressure and gravity? How might these have changed how a civilization might achieve technology advances we consider necessary to get off the planet?

There are science fiction stories exploring this. Dragon's egg has life on a neutron star, Mesklin is a fictional planet with high g where multiple stories happen.

 

[Suppaman]

And "Iceworld" has much higher temperatures. It is our scientists that probably should be thinking about more parameters for the Goldilocks criteria. I am not looking for paths to stories, I do my own, but uncovering thoughts on points that appear to have been missed. To arrive at that perfect planet only to find it is not too hot or too cold but too heavy (4 G) and, well, how would 10-20 Bar look to the local inhabitants? I do appreciate the replies I have been receiving, they do make me think. I think I am more interested in what might have evolved in such conditions.

 

[BenAS]

And "Iceworld" has much higher temperatures. It is our scientists that probably should be thinking about more parameters for the Goldilocks criteria. I am not looking for paths to stories, I do my own, but uncovering thoughts on points that appear to have been missed. To arrive at that perfect planet only to find it is not too hot or too cold but too heavy (4 G) and, well, how would 10-20 Bar look to the local inhabitants? I do appreciate the replies I have been receiving, they do make me think. I think I am more interested in what might have evolved in such conditions.

The pressure at the bottom of the oceans on Earth gets as high as ~1000 bars. A lot of life evolves/lives there.

 

[Suppaman]

Yes, but they don't try to light a fire or use vacuum tubes xD