'Super-Earths' in the billions

[Deckerd]

A new estimate by astronomers says 40% of red dwarfs in the galaxy have 'super-Earths' orbiting them.

Link-o-rama

Setting aside the distances involved, which are pretty much insurmountable for the forseeable future, what benefit would something with 10 times the Earth's gravity have for humans?

 

[Maurice]

I don't think it's about human benefit at all, but they're just looking for places where life somewhat as we know it might exist.

 

[Kemaiku]

It would be almost certainly lethal or damaging for organic matter from this planet to exist in such an environment for any length of time. Compressed atmospheres might increase the chances of large amounts of easily accessible surface hydrocarbons though.

Large industrial processes that require huge amounts of compression/pressure would need very little outside help with such a gravity well in effect, and we would have alloys to withstand the outside pressure too.

If we even need anything like that by the time we have workable industrial scale faster-than-light travel.

 

[Asbo Zaprudder]

Ten times the mass doesn't mean ten times the gravitational attraction because the radius of such a body would likely also be greater than that of the Earth. Radius scales as the cube root of mass assuming the same density. Gravitational acceleration at the surface is proportional to mass over radius squared, or the cube root of mass if the density is the same as Earth's. I'd estimate between 2 and 3 times the acceleration due to gravity at the surface. It would be a struggle to move about without mechanical assistance but one's physiology might be able to adapt over time.

 

[Christopher]

Ten times the mass doesn't mean ten times the gravitational attraction because the radius of such a body would likely also be greater than that of the Earth. Radius scales as the cube root of mass assuming the same density. Gravitational acceleration at the surface is proportional to mass over radius squared, or the cube root of mass if the density is the same as Earth's. I'd estimate between 2 and 3 times the acceleration due to gravity at the surface.

That's a good estimate, although you need to keep in mind that a body of the same composition but greater mass would have a greater density, because it would be more compressed by its own gravity. I did some calculations on this a while back. Assuming Earthlike composition (i.e. an iron core making up about a third of its mass), a planet with ten times Earth's mass would have a surface gravity of just about exactly 3 g. If its composition were pure silicate, with no dense iron core, its surface gravity would be just over 2.5 g. And if it had a composition like Mercury, with an iron core making up 70% of its mass, its surface gravity would be 3.8 g.

 

[Asbo Zaprudder]

Not too far out then - thanks, Christopher. I did toy with the idea of varying the composition, but I decided that working out the correct phases/temperatures/densities would need some time on a supercomputer.

 

[Christopher]

^The thing is, I can't even remember how I did the calculations for my spreadsheet page. I think I found a paper about super-earths that had tables of mass and radius, and I copied those figures into the spreadseet and computed the gravity and density from those. Or maybe I found a graph of mass vs. radius and estimated the radius figures from that, in which case my calculations would be a little rough. But they're good enough as ballpark estimates for my science-fiction worldbuilding.

 

[Asbo Zaprudder]

That would be my approach as well. It's a complex subject. There's some debate as to whether the Earth is at some sort of sweet spot for favouring the development of plate tectonics, or whether it's at the lower limit of the range with super-earths having more vigorous tectonic activity. I suspect that the abundance of liquid water on the surface plays some part but it looks like a nifty research area for someone (other than me).

 

[Kemaiku]

Gravitational acceleration at the surface is proportional to mass over radius squared, or the cube root of mass if the density is the same as Earth's. I'd estimate between 2 and 3 times the acceleration due to gravity at the surface.

That's a lot more liveable, if with a good deal of difficulty. Would the use of pressure suits similar to those used in the airforce for high-g producing speeds be of much use in that environment?

If so then it would be a hostile terrain still but with personnel working the machinary on the surface, industrialisation is still workable. A planet that large might undergo similar compression during it's formation to cause Uranium and other heavy metals to form, possible larger ones into the transuranic series.

 

[Crazy Eddie]

A new estimate by astronomers says 40% of red dwarfs in the galaxy have 'super-Earths' orbiting them.

Link-o-rama

Setting aside the distances involved, which are pretty much insurmountable for the forseeable future, what benefit would something with 10 times the Earth's gravity have for humans?

Assuming you could acclimate to that much gravity, it would be the ultimate training world. You could raise an army of super soldiers just by moving your training facilities to those high gravity worlds; within a year, you'll have troops with extremely high bone and muscle density, superior endurance and agility in any normal environment. They would gain immense physical strength just by virtue of the extreme minute-by-minute loading on their bones and muscles, even if they weren't physically training.

 

[Kemaiku]

Wouldn't they then be unable to move properly on Earth, overcompensating and moving with too much force until they learned to restrain their movement? getting worn down too fast from all that muscle mass, having too eat their weight in protein to even sustain it?

 

[Christopher]

That's a lot more liveable, if with a good deal of difficulty. Would the use of pressure suits similar to those used in the airforce for high-g producing speeds be of much use in that environment?

I doubt it, since they're sitting down in their planes and don't actually need to exert their muscles to move against that kind of gravity. What you'd need is something like the strength-enhancing armatures that have been developed for the military in recent years.

A planet that large might undergo similar compression during it's formation to cause Uranium and other heavy metals to form, possible larger ones into the transuranic series.

Physics doesn't work that way. New elements are only created by nuclear fusion in the cores of stars, and elements heavier than iron are only synthesized in supernovae. Those supernovae spew out their material into space in the form of gas and dust containing those elements, and that gas and dust can then form into new stars and planetary systems.

So you're basically getting the cause and effect backward: a protoplanetary disk that's more enriched with heavy elements from supernovae will produce bigger, denser planets. The older the galaxy gets, the more heavy elements get produced by supernovae, and the higher the concentration of heavy elements you'll get in younger planetary systems.

 

[Asbo Zaprudder]

A few other mechanisms have been proposed for r-process nucleosynthesis of heavy elements, such as quark-novae, collapsars, and neutron star collisions.

http://www.sjaa.net/eph/0706/f.html

It has been proposed that some deuterium-deuterium fusion might take place in Jovian-sized planets. Not sure on the state of play on this suggestion.

http://iopscience.iop.org/0004-637X/501/1/367/fulltext/36734.text.html

 

[Christopher]

^In any case, you're not going to get nucleosynthesis in the core of a superterrestrial planet, and certainly not transuranic nucleosynthesis.

 

[Deckerd]

You're just fighting to see who can get the most syllables into one word.

 

[Crazy Eddie]

Wouldn't they then be unable to move properly on Earth, overcompensating and moving with too much force until they learned to restrain their movement? getting worn down too fast from all that muscle mass, having too eat their weight in protein to even sustain it?

Right.

Like I said, super-soldiers.

 

[Asbo Zaprudder]

^In any case, you're not going to get nucleosynthesis in the core of a superterrestrial planet, and certainly not transuranic nucleosynthesis.

The idea was a new one on me, and I'm sceptical, but I wouldn't completely dismiss it out of hand. The nearest thing to a natural nuclear fission reactor was at Oklo in the Gabon. It makes me wonder if a natural fast breeder reactor could also occur in nature. ETA2 - Such a rector would need to use a fluid such as liquid sodium as a coolant, because water is good at slowing down (moderating) the fast neutrons, which are more efficient at converting U238 to Pu239 and less efficient at inducing fission than thermal neutrons. Doesn't seem likely to happen, but then natural fission reactors were a surprise as well.

You're just fighting to see who can get the most syllables into one word.

We need more words like "discombobulated".

ETA: Link to interesting speculation that natural fission reactors might have influenced the development of life on Earth, and that such a reactor might also have existed on Mars. Probably requires taking with a pinch of NaCl if not a whole bucket.

 

[Christopher]

^In any case, you're not going to get nucleosynthesis in the core of a superterrestrial planet, and certainly not transuranic nucleosynthesis.

The idea was a new one on me, and I'm sceptical, but I wouldn't completely dismiss it out of hand. The nearest thing to a natural nuclear fission reactor was at Oklo in the Gabon. It makes me wonder if a natural fast breeder reactor could also occur in nature. ETA2 - Such a rector would need to use a fluid such as liquid sodium as a coolant, because water is good at slowing down (moderating) the fast neutrons, which are more efficient at converting U238 to Pu239 and less efficient at inducing fission than thermal neutrons. Doesn't seem likely to happen, but then natural fission reactors were a surprise as well.

But that's fission and neutron capture, not fusion. It's pre-existing heavy elements being converted into isotopes of similar mass. It's not the same thing as nucleosynthesis through fusion, not even remotely. Fusion of elements heavier than iron is endothermic -- you have to put more energy into it than you get out of it. So it can't be self-sustaining like a fission reaction. It takes a great deal of energy to fuse heavy elements, especially transuranics which don't occur in nature as far as we've ever discovered. Such things could only be created in supernovae. You can't get transuranic nucleosynthesis in the core of a superterrestrial planet any more than I could crush coal into diamonds with my bare hands.

 

[Kemaiku]

Physics doesn't work that way. New elements are only created by nuclear fusion in the cores of stars, and elements heavier than iron are only synthesized in supernovae.

Fair enough, I got the mechanism wrong, but aren't larger stars than our own more common? I thought in order to have stars like red and yellow giants with proportionally larger planets like the super-Jovians and super-Earths, it would require the system to form from the remnants (super/hypernovae clouds) of larger first-generation stars, the heavier ones that would have had the ability to fuse elements to the Uranium part of the table?

Well even if no deposits of heavier elements exist such a planet would have a lot of materials like iron and silicon compounds, hydrocarbons and so on. Actually, elements only so far as titanium and lead on the periodic table in those quantities would be worth it alone.

 

[CorporalCaptain]

especially transuranics which don't occur in nature as far as we've ever discovered

This isn't completely true, though it almost is.

From http://en.wikipedia.org/wiki/Plutonium:

Plutonium is the heaviest primordial element by virtue of its most stable isotope, plutonium-244, whose half-life of about 80 million years is just long enough for the element to be found in trace quantities in nature.[3]
(...)
3. ^ Hoffman, D. C.; Lawrence, F. O.; Mewherter, J. L.; Rourke, F. M. (1971). "Detection of Plutonium-244 in Nature". Nature 234 (5325): 132–134. Bibcode 1971Natur.234..132H. doi:10.1038/234132a0.

Still, the discovery of natural plutonium was quite a coup.

See also http://en.wikipedia.org/wiki/Primordial_element and http://en.wikipedia.org/wiki/Nucleosynthesis.

Almost all transuranic isotopes don't have long enough half-lives to last from any primordial event that might have created them to be detected.