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

[Czcibor]

Yes, I know, a civilization able to send a colony spaceship on distance of many light years wouldn't probably be very sensitive to a harsh climate...

Assumptions:
- well within habitable zone;
- there is some local life that was able to generate atmospheric oxygen;
- you can pick a whichever place good place on its surface;
- no cheating, no GMO humans; ;)
- if any lucky but possible additional natural processes were needed please assume them but list them.

With ex. 8 Earth masses it should roughly (ignoring matters of density) it should have roughly twice Earth gravity. Crushing, but not directly lethal for unprotected human.

Do it have to be a water world? Would it have to have ultra dense atmosphere? (Could some lucky strike of a planet size object strip it of its volatiles, thus preventing appearance of water world with ultra dense atmosphere)

How would look its plate tectonic? Would it be relatively flat because of gravity, or with such mass it would be so geologically active that mountainous landscape would anyway appear?

 

[mfb]

- there is some local life that was able to generate atmospheric oxygen;

Do not expect that this life will produce anything edible. At the same time, do not expect that our immune system knows how to deal with any life there, so maybe humans just get eaten (cell by cell) by something similar to bacteria.

Would it have to have ultra dense atmosphere?

Maybe, depends on the situation (especially the type of the star).

How would look its plate tectonic?

Publish it, if you find a good answer ;).

Gravity, atmospheric density, winds, rain (or similar), type of rock... all relevant for surface structures.

 

[Drakkith]

- no cheating, no GMO humans; ;)

What is a GMO human? Genetically modified? If so, why not? I personally expect this to be a requirement if we are going to colonize planets that already have life adapted to them.

With ex. 8 Earth masses it should roughly (ignoring matters of density) it should have roughly twice Earth gravity. Crushing, but not directly lethal for unprotected human.

That's pretty high. Just breathing while lying down would probably take effort. At least at first. Perhaps the people would adapt and build up muscle to counteract it. Keep in mind that this is much worse than someone simply weighing twice as much here on Earth due to obesity. Imagine your head weighing twice as much as it does. It would probably give you severe neck issues. On Earth gravity is still 1g, so even if you are fat you can mitigate some of that extra weight by letting it rest on the ground or your chair or whatever. The only time you really support all of it is when you are standing.

Do not expect that this life will produce anything edible. At the same time, do not expect that our immune system knows how to deal with any life there, so maybe humans just get eaten (cell by cell) by something similar to bacteria.

You know, I've never really thought much about immunity vs local organisms. I suppose its possible, if not probable, for either ourselves to be completely immune to practically everything on the planets, or extremely vulnerable to said organisms?

 

[Antiphon]

Don't forget protein chirality. There's a 50-50 chance that nothing growing or living there can be digested or metabolized at all.

 

[mfb]

Don't forget protein chirality. There's a 50-50 chance that nothing growing or living there can be digested or metabolized at all.

If different types of chiral molecules are independent of each other, it might look different. However, we do not even know if other life uses proteins similar to ours at all.

I suppose its possible, if not probable, for either ourselves to be completely immune to practically everything on the planets, or extremely vulnerable to said organisms?

We have so many different types of bacteria on earth, digesting so many different things. I would expect to see some types which can digest human cells. Well, that is quite speculative with just one example of life on a planet.

 

[Czcibor]

Don't forget protein chirality. There's a 50-50 chance that nothing growing or living there can be digested or metabolized at all.

Oh, come on, local organic material can be converted before consumption to simple, easy to digest compounds like ethanol

From practical reasons one can bring his own species, so chirality would hamper habitability seriously.

What is a GMO human? Genetically modified? If so, why not? I personally expect this to be a requirement if we are going to colonize planets that already have life adapted to them.

Why not? Because it changes the question from "how could such planet look like?" to "what can we achieve with GMO?" Thus the proper subject would cease being "General astronomy" and the topic in such a case shall be moved to "Biology" or "Medical Sciences". Yes, realistically, the main reason why a civilization that goes on inrastellar travel is not GMO, is that's already dominated by AI that treat all carbon life forms as outdated model. ;)

 

[sikrut]

Yes, I know, a civilization able to send a colony spaceship on distance of many light years wouldn't probably be very sensitive to a harsh climate...

I wouldn't make this assumption. Having organisms living for years and years on such a vessel might make them more sensitive to a harsh climate than before they embarked on the journey, and maybe even sensitive to small variations in climate. To live in a regulated environment for years on end, where large, planet-like temperature fluctuations are rare could inevitably mitigate the colonists ability to adapt.

 

[twofish-quant]

It's a bit more than chirality. All multi-celluar life on the Earth using a particular amino acid code, and it's likely that any life on another planet would use a different code. It might be possible to break things down, but it's not clear how fermentation would work or whether it would work at all.

One other thing is that there are likely to be some interesting interactions between any bacteria you bring and any local organisms.

Why not? Because it changes the question from "how could such planet look like?" to "what can we achieve with GMO?" Thus the proper subject would cease being "General astronomy" and the topic in such a case shall be moved to "Biology" or "Medical Sciences".

It would be a subfield of astro-biology. Also one thing that becomes pretty quickly obvious is that it's easier to solve the problems of interstellar travel through biology rather than engineering. It's probably a lot easier to design a human body that can live for 600 years than it is to accelerate a starship to 0.9c.

Yes, realistically, the main reason why a civilization that goes on inrastellar travel is not GMO, is that's already dominated by AI that treat all carbon life forms as outdated model. ;)

Then you get into some interesting politics. In the 1960's it was pretty obvious that humanity would colonize the stars because it was there. Right now, we are having problems even getting into low Earth orbit.

There's an interesting paradox. A lot of the motivation for getting off the planet was because we had two superpowers in a life and death struggle. Without this sort of struggle, no one is interested in getting off the planet. With that struggle, you end up risking total war that destroys the planet. So to get into space, you need just enough conflict to force people off the planet, but not so much that it destroys the planet.

 

[Antiphon]

I'm still interested. The world is even less safe than it was in the Cold War and an extinction-level impact could always be right around the corner.

 

[Drakkith]

I'm still interested. The world is even less safe than it was in the Cold War and an extinction-level impact could always be right around the corner.

How is the world LESS safe now? Without two superpowers primed to annihilate each other and most of the world it sure seems a whole lot safer to me.

 

[Ryan_m_b]

Some initial thoughts:

1) Twice Earth gravity is quite dangerous. It's analogous to walking around with a twin on your back. Any fall is going to have the potential for serious injury or death and I can't imagine the strain on the colonists joints and cardiovascular system. On top of that we have no idea what the long term health effects (especially during development) are for living out of Earth gravity. Astronauts spend a few months in freefall and have to fight of a plethora of problems, going from conception to adulthood is likely to be even more complicated.

2) A planet that massive is likely to have a much thicker atmosphere which in turn would heat up the surface no?

3) The chances of the local ecology being compatable are slim to nil. Bear in mind that we can't safely eat the majority (or close to I would argue) of organisms found on our own planet. We evolved to live in a very specific ecological niché, just because we've spread around the planet doesn't mean we can jump of it easily. Leaving aside matters of chirality it might not even opperate on the same fundamental biochemistry. On top of that even if the local ecology is close enough to be compatible with us then within minutes of stepping out the airlock a superantigen would probably kill everyone. If not that then some form of infection we have no immunity from.

I'm sorry but space is not the New New World. You can't get there on the cheap with a brace of pioneers and hack out a society in the new fertile land.

 

[Chronos]

It is unclear how biochemical processes might evolve under massive gravity. My guess is it would be different from earth. In fact, I doubt biochemical processes would evolve similar results to those on Earth under identicaly initial conditions.

 

[mfb]

On top of that even if the local ecology is close enough to be compatible with us then within minutes of stepping out the airlock a superantigen would probably kill everyone. If not that then some form of infection we have no immunity from.

Just thinking... if that is possible (and as you can see from post 2 and 5, I think it is), it might be a serious threat for humans on earth: someone could design such a thing.
If it is completely different from life on earth, it might work the other way round, too - organisms on Earth might digest it, and the species on Earth (=the possible number of thing-digesting species) would outnumber the designed things by far.

 

[Ryan_m_b]

Just thinking... if that is possible (and as you can see from post 2 and 5, I think it is), it might be a serious threat for humans on earth: someone could design such a thing.
If it is completely different from life on earth, it might work the other way round, too - organisms on Earth might digest it, and the species on Earth (=the possible number of thing-digesting species) would outnumber the designed things by far.

True though there are enough deadly attributes in terrestrial organisms that very successful bioterrorism could simply stem from combing them (for example inserting NDM-1 into a plethora of deadly and contagious but currently treatable pathogens)

 

[Czcibor]

Some initial thoughts:

1) Twice Earth gravity is quite dangerous. It's analogous to walking around with a twin on your back. Any fall is going to have the potential for serious injury or death and I can't imagine the strain on the colonists joints and cardiovascular system. On top of that we have no idea what the long term health effects (especially during development) are for living out of Earth gravity. Astronauts spend a few months in freefall and have to fight of a plethora of problems, going from conception to adulthood is likely to be even more complicated.

Harmful - yes, immediately lethal - not. Actually there are people with my height and twice my mass who are alive and able to walk.

2) A planet that massive is likely to have a much thicker atmosphere which in turn would heat up the surface no?

Merely more effective greenhouse effect is not a problem, just the planet would have receive less energy from its star for everything to level out.

I'm more afraid of high atmospheric pressure which, pending on composition means: oxygen poisoning/ carbon dioxide poisoning /nitrogen anaesthesia.

3) The chances of the local ecology being compatable are slim to nil. Bear in mind that we can't safely eat the majority (or close to I would argue) of organisms found on our own planet. We evolved to live in a very specific ecological niché, just because we've spread around the planet doesn't mean we can jump of it easily. Leaving aside matters of chirality it might not even opperate on the same fundamental biochemistry. On top of that even if the local ecology is close enough to be compatible with us then within minutes of stepping out the airlock a superantigen would probably kill everyone. If not that then some form of infection we have no immunity from.

I agree that the chance of edible local organism are low. On the other hand bringing your own plants and animals sounds as rather simple solution. Yes, presumably some of them might become invasive specie and cause local disaster. Concerning allergy (or oppositely lack of sufficient reaction of our immune system) - hard to say. I'm not specially afraid of contracting tobacco mosaic virus ;)

So -rephrasing my question - is some kind of stripping of atmosphere and hydrosphere a realistic scenario for some superEarth's? (I think about collisions) Should the landscape be flattened by gravity or not so much? (I'm curious because it might be possible that the most friendly place could be mountain ranges)

 

[Ryan_m_b]

I only have time for a quick post from my phone but regarding mass it isn't analogous to bigger people, your body adapts to your size as it changes but in this case the mass of everything is different. I question the ability to adapt to that. Also falling 1 metre is as dangerous as falling 2 on Earth as everything will accelerate faster.

Regarding bringing terrestrial organisms the complexity of biospheres is utterly non trivial. Throwing down some life in a world it is not adapting to is not going to give you a pop up biosphere.

 

[Damo ET]

The gravity problem would be a non issue for the body to handle. The traveling spacecraft would just have to be put into a spin to simulate the gravity on the 'new' planet for the last 6 months of travel time to bulk up Arnie style! The crew would have to consume a calcium rich food source to increase bone density also.


Damo

 

[Ryan_m_b]

The gravity problem would be a non issue for the body to handle. The traveling spacecraft would just have to be put into a spin to simulate the gravity on the 'new' planet for the last 6 months of travel time to bulk up Arnie style! The crew would have to consume a calcium rich food source to increase bone density also.


Damo

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]

Regarding bringing terrestrial organisms the complexity of biospheres is utterly non trivial. Throwing down some life in a world it is not adapting to is not going to give you a pop up biosphere.

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.

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.

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/article/0,9171,897495,00.html

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

 

[Czcibor]

EDIT:
I found something better:

The experimental animals were in good general health throughout this study, as determined by the daily examinations by animal care technicians. Food consumption showed a transient decrease on centrifugation onset, which returned to normal in ∼4 days. Our laboratory has previously reported for this study (39) that there were no statistical differences in food intake among groups on days 11-14 (food intake, g/body mass2/3). This is consistent with a previous study (34) that indicated that average food consumption showed no significant variation when rats were exposed to 1.75 G for up to 40 days. Another indication that our animals were in good health was that urinary corticosterone excretion (days 11-14, ng/mg urinary creatinine) was similar among groups (39).

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 traveling 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]

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.

I didn't suggest that carrying twice as much weight represented 2G.
Artificial gravity created by a spinning spacecraft 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 spacecraft 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]

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.

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.

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?

See two posts above.

 

[Ryan_m_b]

Still traveling 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]

you'll get toasted at body temperature + 50 degrees, within minutes.

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]

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

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.

www.esa.int/esaMI/Cassini-Huygens/SEMPQ6HHZTD_0.html

 

[ImaLooser]

You know, I've never really thought much about immunity vs local organisms. I suppose its possible, if not probable, for either ourselves to be completely immune to practically everything on the planets, or extremely vulnerable to said organisms?

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

Basic rule of space exploration.

 

[mfb]

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

Basic rule of space exploration.

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?