Could a superearth be hospitable (survivable?) for humans?

Ryan_m_b

Living in 2g is not equivalent to carrying twice as much weight in 1g. If this thread is going to crassly ignore any biological considerations in favour of bold assertions then it will be locked.

Let's start discussing the science properly people.

Czcibor

But who asked for full bioshpere? Assuming that Earth plants are adapted well enough to survive and have no natural enemies - they look like potentially invasive specie. What would humans really need is few monocultures able to produce edible crops, nothing more.

So far your crucial scientific argument here is that you have moderator privileges. You unquestionably have that, but that's argumentum ad baculum, which is only partially convincing, at best.

I agree that trying to treat is 2g as carrying twice as much is indeed oversimplification, and if possible should be replaced with more nuanced approach. So your more nuanced idea is? (I can't think anything much better now but if you want to place some more useful input I'd grateful. So far you had an interesting point with objects falling quicker because of higher gravity)

Concerning adaptation of joints, bones and muscles - do you consider that in that area "carrying double weight" would be so bad approximation? I mean for blood system that indeed might be trickier.

The best that I could find was about mice that were able to reproduce at 2gs.
http://www.time.com/time/magazine/ar...897495,00.html

I'm also curious at how high gravity you'd put threshold for human adaptation limit.

Czcibor

EDIT:
I found something better:
Source:
http://jap.physiology.org/content/95/3/1266.full

Ryan_m_b

Excellent! Isn't it better when we have something tangible to look at and discuss? I'm travelling this weekend and participating by phone is arduous but will read through the links when available.

P.s; I'm less happy about accusations that I've been abusing moderator status. At no point did I insist I was correct and tried to back that up with my position.

mfb

One problem at 2g: Blood pressure. A regular lower pressure in a horizontal position is about ~10kPa, or ~1m of water at 1g. At 2g, this is just ~50cm, and might give serious issues with blood pressure in your head when you are standing. You would probably need a permanent hypertension just to stay conscious.

Tests with mice do not see this effect, as mice are too small.

Damo ET

I didn't suggest that carrying twice as much weight represented 2G.
Artificial gravity created by a spinning space craft would simulate all the aspects of the extra gravity, from humans to the plant life which would also need to adapt to the extra gravity.
One of the main issues would be the size of the craft to be able to replicate consistent 'gravity' from head to toe, as the smaller the craft, the bigger the difference.
http://en.wikipedia.org/wiki/Artificial_gravity
But, if this was a reality, the guys building and sending the space craft off would know this already and it would also be a non issue.
Average bone density and a higher muscle mass would need to be increased to deal with the additional weight, this could be achieved via a specific diet in the last months of travel.
I am not sure which biological considerations have been missed?


Damo

mfb

I don't think that is important. If you sit or lie, you even get a completely different direction of gravity for some body parts.
I would be more concerned about coriolis force.

See two posts above.

Ryan_m_b

Still travelling but quick point for consideration: the mass of bone and muscle will itself be different. The attempt by the body to adapt may be hampered by the difference in mass for the new bone/muscle to what the body is "expecting". My biggest concern (other than development) is that of the joints, a body builder could weigh up to a quarter of a tonne in a 2g environment. That's a lot of strain on ankles, knees etc.

chill_factor

i think it would be almost unsurvivable except by a few sorts of athletes, astronauts and other highly conditioned and trained people.

your veins would struggle to return blood to your heart. that's a big problem.

http://en.wikipedia.org/wiki/Venous_return

if you fell down from what's a minor step, it would be very serious.

also, your spinal cord does not appreciably increase in strength regardless of how much exercise you get or how much you eat. but the spinal cord is the only thing supporting your head.

finally, adaptability is not symmetric. humans can survive body temperature - 50 degrees for hours. you'll get toasted at body temperature + 50 degrees, within minutes. adapting to 0 g is much much much easier than adapting to 2 g.

this is just the gravity aspect.

mfb

Saunas are not deadly within minutes (usually), but the asymmetry is there, of course.

There are centrifuges where it would be possible to test the influence of 2g for more than several minutes (=typical timescale of a rocket launch), but I don't know of long-term tests there.

Damo ET

Well, 'we' would probably have to go down the path of an exoskeleton (partial at least) when moving around on the planet itself, to counter all of the effects of the extra gravity. Seems like it would be better overall option.
But what about the plants? Has anyone experimented growing things in a higher gravity state?


Damo

Drakkith

An exoskeleton, while nice to have if you have to move things around, doesn't help the internal stresses the body would face.

SW VandeCarr

I don't know your requirements for a habitable super-earth, but if you're willing to accept the smaller gas giants beyond Jupiter, they all have near earth gravity and not too far below the gas "surface" there's liquid water and earth like temperatures (at least for Saturn). One could conceivably have floating colonies there.

In the extreme, the planet could be "wrapped" creating a huge surface area heated from below, with 1 g gravity and an atmosphere created from venting a selected proportion of gases from the interior. Since we are in the area of semi-plausible sci-fi, the wrapping could be accomplished by microorganisms adapted to a particular atmospheric level, using CO2 and methane as a carbon source and whose product forms dense floating webs that eventually interconnect.

http://www.esa.int/esaMI/Cassini-Huy...Q6HHZTD_0.html

ImaLooser

If you can't digest it, it can't digest you.

Basic rule of space exploration.

mfb

Please provide a source (or at least a good reason) for that claim.

Here are counterexamples to take into account:
We can digest plants, but how can plants digest us?
Viruses can digest us, but how can we digest viruses?