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Hydrogen dominated terrestrial worlds


Moontanman

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This paper suggests some very interesting possibilities about life on other planets. Dense hydrogen atmospheres might support life on super Earth type planets!

 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284464/

 

 

 

Abstract

The diversity of extrasolar planets discovered in the last decade shows that we should not be constrained to look for life in environments similar to early or present-day Earth. Super-Earth exoplanets are being discovered with increasing frequency, and some will be able to retain a stable, hydrogen-dominated atmosphere. We explore the possibilities for photosynthesis on a rocky planet with a thin H2-dominated atmosphere. If a rocky, H2-dominated planet harbors life, then that life is likely to convert atmospheric carbon into methane. Outgassing may also build an atmosphere in which methane is the principal carbon species. We describe the possible chemical routes for photosynthesis starting from methane and show that less energy and lower energy photons could drive CH4-based photosynthesis as compared with CO2-based photosynthesis. We find that a by-product biosignature gas is likely to be H2, which is not distinct from the hydrogen already present in the environment. Ammonia is a potential biosignature gas of hydrogenic photosynthesis that is unlikely to be generated abiologically. We suggest that the evolution of methane-based photosynthesis is at least as likely as the evolution of anoxygenic photosynthesis on Earth and may support the evolution of complex life.

 

 

Does this suggest that fire could take place?

 

 

 

Secondly, oxidative metabolism yields so much energy because of the food it has to oxidize. Carbohydrates and fats are the storage materials that plants and animals chose to use exactly because they are the most efficient ways of storing energy in an oxidizing environment. However, they are not the only storage option. Predatory plankton preying on phytoplankton gain substantial energy from the metabolism of dimethylsulfonium proprionate (DMSP), releasing dimethyl sulfide (DMS) in large amounts [103,104]. DMSP is accumulated for reasons other than energetics (no one has convincingly argued what those reasons are [104,105,106]). Its energy of hydrolysis would be the same in oxidizing or reducing environments. In a reducing environment, highly oxidized compounds could be stored as energy storage materials, having the highest energy density when reduced with hydrogen, or other compounds with roles comparable to DMSP could be accumulated and be used as high-energy food. The absence of oxygen does not therefore preclude the possibility that other biomass components could be metabolized to yield lots of energy per gram.

 

Would this indicate that hydrogen breathing life forms on super earths dominated by hydrogen might be more common than oxygen dominated terrestrial planets? If so what could this indicate for exo life and our search for such life?

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Hey guys, we have discussed worlds with hydrogen breathing life forms and the main stumbling block has been how do you develop technology with out fire!

 

Now it looks like fire might be possible after all, this may very well suggest that we oxygen breathers may be a minority so this is just one more way we are not special!

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This is awesome. I don't suppose we have any plants here on earth that can survive on a planet with a hydrogen dominated Atmosphere.

 

 

That is an interesting question and could be a good experiment... I'm betting that some cyanobacteria could do it, not so sure about higher plants..

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That is an interesting question and could be a good experiment... I'm betting that some cyanobacteria could do it, not so sure about higher plants..

 

Drop some cyanobacteria on a hydrogen planet, and see how it evolves. We could probably make lab conditions close to that of the planet's and see what happens here on earth
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Drop some cyanobacteria on a hydrogen planet, and see how it evolves. We could probably make lab conditions close to that of the planet's and see what happens here on earth

 

 

There are bacteria that photosynthesize and live in anoxic conditions, can you imagine how bad oxygen would smell to creatures that evolved to breath hydrogen?

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There are bacteria that photosynthesize and live in anoxic conditions, can you imagine how bad oxygen would smell to creatures that evolved to breath hydrogen?

 

Can bacteria smell? I think once we find hydrogen breathing things that can smell, we hit organisms. But yeah, oxygen we bemcoming out of a skunks behind.
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Gee whiz guys is this paper really that uninteresting? I am have been obsessing over it for days an what it would mean for the prospects of extraterrestrial life not to mention the wild stories that could be written about such a weird place! Thank you for your replies
Raider5678

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There's a sequel?

 

Also, do you know the percentage of planets that would have these conditions? It may have been in the paper but to be honest it lost me in some areas.

 

 

I watched the talk by a NASA scientist any the consensus was that such planets would be more common than earth, if for no other reason than it broadens the life zone around stars. Couple that with hydrogen being the most common element in the universe and the fact that it could be used as a breathing gas would seem to open up lots of possibilities that were not known when calculations about life in the universe was made...

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  • 2 weeks later...
Planets with a very dense gaseous envelope (“sub-Neptunes”) will have a surface too hot for liquid water, if they have a defined surface at all (Seager and Rogers in preparation). However rocky planets with a thin, hydrogen-dominated atmosphere can have a surface temperature compatible with liquid water. H2:H2collision-induced absorption (CIA) of near-infrared (NIR) light provides a strong greenhouse effect [47,48], which can mean that such planets have surface temperatures compatible with liquid water well outside the conventional “habitable zone”. Thus, the habitable zone for super-Earths with a H2-dominated atmosphere can be much more extensive than that for truly Earth-like planets (reviewed in [49]). However, there are limits to the extension of the habitable zone for a planet with an H2-dominated atmosphere. In general, the atmospheric greenhouse effect caused by H2-H2 CIA will increase with increasing atmospheric depth, but the attenuation of light reaching the surface will also increase with atmospheric depth. For a very dense atmosphere, surface photosynthesis will not be possible, because the surface will be dark. We return to this inSection 3.6 below.

 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284464/

 

Exciting news guys. With hydrogen gas so widely spread, it may just be possible that living things with a large surface area:volume ratio could diffuse methane across their surface and turn out hydrogen as a by-product. However, bacteria or singe celled organisms would be dominant and not some multicellular floozy waiting to seduce a future Captain Kirk :) . However, from my sketchy reading, which could be incorrect as I as having a conversation at the same time, the composition of these planets needs to have a mineral content similar to that of Earth. The reason for a thin layer of atmosphere is justified above.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284464/

 

Exciting news guys. With hydrogen gas so widely spread, it may just be possible that living things with a large surface area:volume ratio could diffuse methane across their surface and turn out hydrogen as a by-product. However, bacteria or singe celled organisms would be dominant and not some multicellular floozy waiting to seduce a future Captain Kirk :) . However, from my sketchy reading, which could be incorrect as I as having a conversation at the same time, the composition of these planets needs to have a mineral content similar to that of Earth. The reason for a thin layer of atmosphere is justified above.

 

 

Thank you Jimmy, I was beginning to think I was being ignored! Disagree sure but to be ignored is bad!

 

Yes, it would seem that some hope exists for hydrogen breathers, I remember Issac Asimov say that the energy deficit could be made up by the fact that high pressure hydrogen would contain far more hydrogen atoms per "lung full" than an oxygen atmosphere like ours.

 

The key that really excited me about this was the possibility that on a hydrogen world energy could be stored by plants making oxidizers, the opposite but similar way that in our atmosphere plants make and store energy in the form of carbohydrates, pretty much a mirror image of our own world. But more importantly if plants stored oxidizers then fire would be possible and by extension technology!!!

 

A hydrogen world would not be limited to a stone age civilization!

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Because this paper is concerned with possible photosynthesis reactions on an inhabited planet, we will consider the third of these scenarios, one in which atmospheric carbon is present primarily or exclusively as methane. We note that the third scenario is itself indicative of the presence of life, i.e., the presence of methane and the absence of carbon dioxide is a weak biosignature in its own right, even in an H2-dominated atmosphere.

 

 

Methane is the most reduced form of carbon, so in order to build complex molecules, it must be oxidized. In a reducing environment, oxidizing methane will require energy, which here we assume comes from light. The analogous reaction to Reaction (1) above is therefore

CH4 + H2O + hv→CH2O + 4[H]
(4)

 

A simple version of this reaction would be one that generated hydrogen gas, thus:

CH4 + H2O + hv→CH2O + 2H2
(5)

 

 

 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284464/

 

This could be the biosignature which, if identified, could change the history of our planet - low carbon dioxide, ammonia and hydrogen together as a ratio could indicate a form of life, especially if the gas composition fluctuates, as methane is consumed by alien photosynthetic bacteria or algae. So, if I read it correctly, we would need a rocky planet, with similar mineral composition to the Earth and the presence of simple organisms could utilise the light from their close Sun-like star to turn methane into atmospheric hydrogen. and biomass in the form of carbohydrate. Just one word: WOW!

Edited by jimmydasaint
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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284464/

 

This could be the biosignature which, if identified, could change the history of our planet - low carbon dioxide, ammonia and hydrogen together as a ratio could indicate a form of life, especially if the gas composition fluctuates, as methane is consumed by alien photosynthetic bacteria or algae. So, if I read it correctly, we would need a rocky planet, with similar mineral composition to the Earth and the presence of simple organisms could utilise the light from their close Sun-like star to turn methane into atmospheric hydrogen. and biomass in the form of carbohydrate. Just one word: WOW!

 

 

 

NASA suggests life on Saturn's moon Titan http://www.nasa.gov/topics/solarsystem/features/titan20100603.html

 

How ever, once life gets started... I wonder if complex intelligent life on a hydrogen world sits around wondering if complex life could survive in the presence of what to them must be a poison.. oxygen?

 

Can you point me to where the paper says that only fungi and bacteria would be possible on such a world?

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Photosynthetic bacteria also oxidize sulfide to sulfate and hydrogen to water (reviewed in [38]). Both the oxidation of sulfur to sulfate and the oxidation of hydrogen are energy-releasing reactions on Earth, and so the light capturing apparatus is being used in these organisms as a supplement to chemosynthetic processes and not as the primary energy source.

We might therefore suspect that life on a hydrogen-dominated world might evolve photosynthetic chemistry that does not produce hydrogen (“anhydrogenic” photosynthesis) if suitable reactions are available.

Anhydrogenic photosynthesis might dominate if: (1) the mechanisms for hydrogen evolution had not evolved; (2) light energy was a limiting resource, and reactions that required less energy were available; (3) a source of hydrogen atoms to build into H2 was limiting; or (4) some combination of these. The next sections address the overall energetics of hydrogenic photosynthesis and the relative energetics of hydrogenic vs.anhydrogenic photosynthesis.

I am assuming that the paper is restricted to photosynthetic bacteria making carbohydrates and other macromolecules (proteins, fats) in bacterial form that turns methane into hydrogen and carbohydrate. they mention Earth bacteria as analogues and extend the argument. Algae are not mentioned clearly - I assumed that one. Sorry.

 

Edited by jimmydasaint
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I am assuming that the paper is restricted to photosynthetic bacteria making carbohydrates and other macromolecules (proteins, fats) in bacterial form that turns methane into hydrogen and carbohydrate. they mention Earth bacteria as analogues and extend the argument. Algae are not mentioned clearly - I assumed that one. Sorry.

 

 

 

Ok, I thought you were saying that the paper asserted that no complex life forms could evolve, miss understanding, no problem...

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I looked at this a bit deeper, it suggests that about 30 bar is the limit for light to penetrate to the surface, but we can hypothesize a planet, maybe 20,000 miles in diameter. 10 - 20 bar atmosphere of mostly hydrogen. 12 times earths mass, less dense but 2 gravities at the surface, 15.6 times earths volume, 6.25 times the surface area. It would be difficult to escape using chemical rockets but nuclear should do it... day length could be anything, but longer days seems likely to me 36 hours, just arbitrary on that, a couple Titan sized moons... Is this planet more likely than Earth?

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If all the hydrogen becomes metallic then the atmosphere would be almost entirely liquid helium which is completely transparent to infrared (because its monatomic)

Edited by granpa
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If all the hydrogen becomes metallic then the atmosphere would be almost entirely liquid helium which is completely transparent to infrared (because its monatomic)

 

 

It's also usually associated with very high heat and very high pressure like neptune or uranus, thousands if not millions of bar...

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