Writing help - Ocean World

[DaveC426913]

I'm writing a science fiction short story about an ocean world with indigenous life, colonized by humans, and I want to check some of my "facts".1.
Given the possibility/assumption of panspermia, spreading hydrocarbons and possibly even simple enzymes between systems, is it plausible for a habitable planet to produce complex life forms that share at least marginally metabolizable compounds with us even if they didn't develop the same DNA?

(I find it stretching the limits of plausibility that an ecosphere on a distant planet would use DNA - even if it started with mostly the same components as us. It might be similar in function to DNA but I find it hard to believe DNA is the one possible molecule that can develop complex life.)

How similar (and thus, how less plausible) would an alien ecology's chemical structure have to be to be marginally metabolizable by humans (if not wholly nutritious)? Alternately, how dependent on the DNA molecule itself are the proteins we need for nutrition?

I know we need carbs - but they're pretty simple. I know we need proteins but they're super complex and, in my opinion, very unlikely to match ours.

But what if the breakdown could be helped along? Say, a chemical additive that would break down alien proteins enough that they were usable by us?

Maybe it would only have to be for short durations i.e.a trip into the wild - as long as they got back on human food in some reasonable time-frame - or could at least supplement their diet with human food for the duration.

Assume technology and bio-chemistry is a century ahead of ours. Assume colonists have had some decades to work on the problem.2.
How difficult might it be for an alien organic critter to emit and detect radio waves? (How/why they evolve this - and the energy budget it might cost - might be another matter.)

Most Earth marine species can detect electricity, and some, such as eels and catfish, can produce it. Is it a big leap to go from electrical pulses to producing bio-chemo-electric sparks (spark-gap radio?), and then to fine-tuning them to produce primitive radio waves? Not hi-rez, like sonar, but they might be able to communicate or sense each other across some distance.

3.
How plausible is a super-Earth ocean world with a goldilocks climate but without the crushing gravity? I was hoping for a world about 1.5 times Earth, but less dense (say, 3g/cm^3), so that its gravity works out to Earth's or less. I looked up ocean worlds and it seems there is an upper limit - that of a small moon. Much larger and the barrier between vapour and liquid and solid seems to disappear. (I guess this plot detail isn't critical. I wanted a vast ocean world but it could simply be an ocean worldlet.)

4.
Can such a world hold on to its atmo? Or will it be stripped away like Mars? Ideally, a thick atmo is better. Looking to build a world where flying is easy.

5.
I'm looking at a primordially radial body plan - like jellyfish and diatoms - as opposed to bilateral. The first life might have been 3-sided, but later mutations produced 4-, 5-, 6- and 8-sided forms, creating the various phyla. Might it be more plausible for mutations to double a symmetry-axis, versus add a symmetry-axis? eg. 3>6>9 versus 3>4>5. Any reason it couldn't be both? eg. 3>6>7.

Thoughts and comments welcome.

 

[BillTre]

1.

Given the possibility/assumption of panspermia, spreading hydrocarbons and possibly even simple enzymes between systems, is it plausible for a habitable planet to produce complex life forms that share at least marginally metabolizable compounds with us even if they didn't develop the same DNA?

Yes.
A common assumption of modern origin of life scenarios is the production of a set of simple organic compounds from which larger molecules are generated. Assuming the same basic chemistry (CHONPS), I would expect the same simple compounds.

(I find it stretching the limits of plausibility that an ecosphere on a distant planet would use DNA - even if it started with mostly the same components as us. It might be similar in function to DNA but I find it hard to believe DNA is the one possible molecule that can develop complex life.)

DNA may not be the only chemical able to do this, but it may be one of a limited number. Besides RNA (RNA world stuff), PNA has been proposed as an ancestral genetic material.

Alternately, how dependent on the DNA molecule itself are the proteins we need for nutrition?

Proteins are sequences of amino acids. Although earthly sequences may be unique to earth, the amino acids seem to be pretty easy to produce abiotically. This makes me think that proteins (strings of AA's) would not be impossibly unlikely. The actual proteins (specific sequences) would depend upon their environment (such as aqueous or non-aqueous) and the functions they fulfill, as well as a the specific AA's that are formed in your location. If something other than DNA or RNA could string together AA's, then they could make a variety of proteins.

But what if the breakdown could be helped along? Say, a chemical additive that would break down alien proteins enough that they were usable by us?

This would be the equivalent of cooking, a human invention that has produced easier to eat and more nutritious meals, yielding more calories for less effort. Maybe heat plus some variant of a microwave oven.
Bacteria in our guts are also a big assist to digestion. They could be engineered for undertaking specific digestions.

2.

How difficult might it be for an alien organic critter to emit and detect radio waves? (How/why they evolve this - and the energy budget it might cost - might be another matter.)

Most Earth marine species can detect electricity, and some, such as eels and catfish, can produce it. Is it a big leap to go from electrical pulses to producing bio-chemo-electric sparks (spark-gap radio?), and then to fine-tuning them to produce primitive radio waves? Not hi-rez, like sonar, but they might be able to communicate or sense each other across some distance.

The weakly electric fish can do this (short range only). They are closely related to the electric eel.
They generate electric pulses from synaptic potentials on one side coin shaped cells (stacked in series to achieve greater voltages).
They generate a local electric field which they use to map their local region and they have an automatic (instinctive) reflex to change they emitted frequencies to avoid jamming by con-specifics.
They (presumably) evolved this as a distance sense in the dark. They can be nocturnal and/or live in very murky water with almost no visibility.
Electrosensitive fish can also use their electrical sense to detect hidden prey (such as buried in the sand) based upon the weak electrical signal from their muscular activities (such as respiration movements).
These can be quite accurate but not long distance.

4.

Can such a world hold on to its atmo? Or will it be stripped away like Mars? Ideally, a thick atmo is better. Looking to build a world where flying is easy.

The stronger the atmosphere the greater likelihood of keeping its atmosphere (unless its too hot).
Smaller planets would have less gravity to overcome for flight. There's a tradeoff there, somewhere.

5.

I'm looking at a primordially radial body plan - like jellyfish and diatoms - as opposed to bilateral. The first life might have been 3-sided, but later mutations produced 4-, 5-, 6- and 8-sided forms, creating the various phyla. Might it be more plausible for mutations to double a symmetry-axis, versus add a symmetry-axis? eg. 3>6>9 versus 3>4>5. Any reason it couldn't be both? eg. 3>6>7.

Jellyfish are related to hydras, anemones, and corals. They are all radial around their top to bottom (oral to aboral) axis and have variants build on that.
Starfish have a secondarially radial body symmetry (subtle hints of their non-radial origibs are retained in their water-vascular system). They (and other animals) can have many stages with different body plans between embryos and adults. They start out bilateral and them coil a repeated structure up on itself. Combinations and variants of these mechanisms could conceivably lead to a variety of x-sided forms.

 

[Rive]

...proteins ... super complex...

Proteins are broken down to amino acids during digestion anyway. What you need are their amino acids, more closely: the essential amino acids, since the human body cannot produce those.
If the life there based on amino acids then I think it is a possibility to have some usable parts.

However, the troubling part is the original function of those proteins. Snake venom and mushroom toxins are too proteins, still we cannot digest them: likely we would have a bunch of inconvenient proteins from an alien life form, even if it is still protein at the end. So maybe better to use that alien life as a raw material processed in a (human-compatible) mushroom growing tank or such instead of trying to digest it directly.

 

[DaveC426913]

Assuming the same basic chemistry (CHONPS), I would expect the same simple compounds.

Yes. I question is more subtle: are those compounds something we can metabolize? r are they too simple?
An extreme example: we need giant protein X. It could be broken down all the way to its component 10,000 atoms - while technically we can meatabolize CHON - it's not in a form we can work with. We need a middle-ground - the most complex common elements. I guess that's the amino acids.

This would be the equivalent of cooking, a human invention that has produced easier to eat and more nutritious meals, yielding more calories for less effort. Maybe heat plus some variant of a microwave oven.
Bacteria in our guts are also a big assist to digestion. They could be engineered for undertaking specific digestions.

Yeah, perfect.

The weakly electric fish can do this (short range only). They are closely related to the electric eel.
They generate electric pulses from synaptic potentials on one side coin shaped cells (stacked in series to achieve greater voltages).
They generate a local electric field which they use to map their local region and they have an automatic (instinctive) reflex to change they emitted frequencies to avoid jamming by con-specifics.
They (presumably) evolved this as a distance sense in the dark. They can be nocturnal and/or live in very murky water with almost no visibility.
Electrosensitive fish can also use their electrical sense to detect hidden prey (such as buried in the sand) based upon the weak electrical signal from their muscular activities (such as respiration movements).
These can be quite accurate but not long distance.

Radio drops off at the same inverse square rate, right? So it's efficacy is specifically limited by strength of signals and by sensitivity of receptors, yes?

One could imagine a race between predators evolving evermore sensitive radio sensors and prey evolving short-term hibernation as a form of evasion.

 

[DaveC426913]

However, the troubling part is the original function of those proteins. Snake venom and mushroom toxins are too proteins, still we cannot digest them: likely we would have a bunch of inconvenient proteins from an alien life form, even if it is still protein at the end. So maybe better to use that alien life as a raw material processed in a (human-compatible) mushroom growing tank or such instead of trying to digest it directly.

A tailored enzyme additive should neutralize specific toxins.

Also, not catching or eating poisonous/venomous critters would solve the problem.The other side of the amino acid metabolization is that - without cumbersome processing factories - the food will surely be an unappetizingly thick, hydrocarbony-tasting goo. Probably taste like gasoline.

 

[BillTre]

Fermentations and pickling processes might also eliminate some toxic materials.

Humans eat some pretty awful tasting things (unless you are already used to the flavor), so taste alone is not necessarily a rule out.

Radio drops off at the same inverse square rate, right? So it's efficacy is specifically limited by strength of signals and by sensitivity of receptors, yes?

One could imagine a race between predators evolving evermore sensitive radio sensors and prey evolving short-term hibernation as a form of evasion.

You might consider colonial organisms that could work as a group to produce stronger signals and greater sensitivity.
A set of colonial organisms might be able to assemble into something like a more effective broadcast or receiving antenna.
Organized colonial activity might be able to overcome many kinds of limitations.

 

[DaveC426913]

Fermentations and pickling processes might also eliminate some toxic materials.

I'm thinking about a trip into the wilderness. Have to carry an absolute minimum of supplies. If they could catch food and treat it, they wouldn't have to carry all their food supply. The treatment would have to be economical in terms of mass, time and room.

Of course, they'd bring dried, powered vitamin supplements as well.

Humans eat some pretty awful tasting things (unless you are already used to the flavor), so taste alone is not necessarily a rule out.

Opportunity for the newbie on the expedition to experience trial-by-fire. Can he keep it down?

You might consider colonial organisms that could work as a group to produce stronger signals and greater sensitivity.
A set of colonial organisms might be able to assemble into something like a more effective broadcast or receiving antenna.
Organized colonial activity might be able to overcome many kinds of limitations.

Ooh! interesting concept! Cooperative predators triangulating to locate a target.

 

[BillTre]

Many organisms (many bacteria and animals at least) can make magnetite crystals, that have been proposed to be involved with detecting direction of magnetic fields. These can be incorporated into living cells.

Other forms of metals (normally toxic) can be excreted (presumably to remove the toxicity). Excreted materials can be used to build large structures, like reefs, shells, etc. (made of calcium carbonate).

Bacteria and archaea have very diverse molecular metabolisms. They all seem to use the same basic core of electron-chemical mechanisms to transfer charge across membranes, in turn to power ATP production, but it can be powered by a large variety of different redox pairs of electron donators and acceptors (oxidizer and reducer chemicals) to drive this apparently ancestral energy generation mechanism.
A diversity of living forms with different and interesting metabolisms could be created based upon these kinds of differences.

 

[DrStupid]

1. Given the possibility/assumption of panspermia, spreading hydrocarbons and possibly even simple enzymes between systems, is it plausible for a habitable planet to produce complex life forms that share at least marginally metabolizable compounds with us even if they didn't develop the same DNA?

Yes, many organic compounds are metabolizable. But some of these substances or their metabolites might be quite unpleasant. Snake venome has already be mentioned above. But it doesn't need to be that complex. There are a lot of small organic molecules with serious effects.

(I find it stretching the limits of plausibility that an ecosphere on a distant planet would use DNA - even if it started with mostly the same components as us. It might be similar in function to DNA but I find it hard to believe DNA is the one possible molecule that can develop complex life.)

It is at least as plausible as proteins. The RNA world has already been mentioned above and you even assume panspermia.

How similar (and thus, how less plausible) would an alien ecology's chemical structure have to be to be marginally metabolizable by humans (if not wholly nutritious)?

For metabolization it doesn’t need to be similar but for nutrition it would need to be almost identical (assuming the huge number of possibilities). Essential amino acids have already been mentioned. It is unlikely that aliens are composed of the same amino acids (if they are made of amino acids at all) as the life we know on Earth.

Alternately, how dependent on the DNA molecule itself are the proteins we need for nutrition?

There is no fixed relation. The same proteins could be coded by completely different DNA and the same DNA could code completely different proteins. It’s just a matter of the genetic code.

But what if the breakdown could be helped along? Say, a chemical additive that would break down alien proteins enough that they were usable by us?

That doesn’t help if the proteins are composed of the wrong amino acids.

Assume technology and bio-chemistry is a century ahead of ours. Assume colonists have had some decades to work on the problem.

Than just assume they use small bioreactors to convert the alien biomass into something useful (e.g. with specifically designed bacteria if you want to go into details).

2. How difficult might it be for an alien organic critter to emit and detect radio waves?

I don’t see a problem in general. However, it doesn't make much sense in water (due to the limited range). In the atmosphere it could be a useful ability.

3. How plausible is a super-Earth ocean world with a goldilocks climate but without the crushing gravity? I was hoping for a world about 1.5 times Earth, but less dense (say, 3g/cm^3), so that its gravity works out to Earth's or less.

Why not? With 3 g/cm³ you get 0.8 g on the surface and with 3.7 g/cm³ it would be 1 g. That sounds plausible. Maybe a small or no iron core and a lot of water could do the job.

Much larger and the barrier between vapour and liquid and solid seems to disappear.

For water this triple point is at 273.16 K and 611.657 Pa. With a dense atmosphere this is not an issue. And even if you have such conditions on your planet - would that be a problem?

4. Can such a world hold on to its atmo?

Yes, even better than Earth. Your planet has around double the masse and the escape velocity is 10..20 % higher.

Ideally, a thick atmo is better.

No problem, but beware of the green house effect when it comes to composition.

 

[DaveC426913]

It is at least as plausible as proteins. The RNA world has already been mentioned above and you even assume panspermia.

Yes. Proteins and RNA are almost as improbable as DNA.

Nevermind independent evolution on an alien planet - they're not even plausible as part of a panspermia scenario.

For metabolization it doesn’t need to be similar but for nutrition it would need to be almost identical (assuming the huge number of possibilities). Essential amino acids have already been mentioned. It is unlikely that aliens are composed of the same amino acids (if they are made of amino acids at all) as the life we know on Earth.

That's why panspermia is a requisite premise. Generally, it's the amino acids that have been postulated as extraterrestrial stowaways.

An alien planet might create some of the same amino acids, but if it has been seeded with amino acids from comet and meteor bombardment, that makes it more plausible.

At the same time, anything more complex than amino acids is too complex to plausibly survive, IMO.

So amino acids are in the sweet spot - simple enough to be transported, but specific enough to direct the development of alien life on a chemically similar path to Earth.

Than just assume they use small bioreactors to convert the alien biomass into something useful (e.g. with specifically designed bacteria if you want to go into details).

Too high-tech. Would alter the story. (OK, so they invented ftl-drive before they invented food processors... )

Think of a 2-person craft, with supplies for a couple of weeks. Now halve that mass (or it would never fly - even in the thick atmo). No power supplies or electronics.

Oh yeah. It can't have any electronic parts. (A premise of the story is a unilateral restriction on all electronics outside settlements. No exceptions.)

I don’t see a problem in general. However, it doesn't make much sense in water (due to the limited range). In the atmosphere it could be a useful ability.

How badly does water limit radio? Assuming the same power output, is a radio signal in water significantly affected more than in air?

Why not? With 3 g/cm³ you get 0.8 g on the surface and with 3.7 g/cm³ it would be 1 g. That sounds plausible. Maybe a small or no iron core and a lot of water could do the job.

Because a little bit of light reading puts an upper limit of the size of terrestrial ocean worlds. Not much bigger than Enceladus.

 

[DrStupid]

An alien planet might create some of the same amino acids, but if it has been seeded with amino acids from comet and meteor bombardment, that makes it more plausible.

I’m not sure if the initial amino acid composition has a significant impact on the amino acid pattern of a biosphere. Amino acids in organisms don’t come from space but are products of complex biochemical pathways. These pathways are the results of billion years of evolution and evolution is quite unpredictable. Even on Earth there are organisms with exotic amino acids (e.g. pyrrolysine) even though they do no just originate from the same primordial soup but from common biological ancestors. It seems implausible that an independent evolution on another planet results in amino acid patterns that are suitable for human nutrition.

At the same time, anything more complex than amino acids is too complex to plausibly survive, IMO.

DNA is pretty stable. Even organisms can survive for a very long time.

While it needs a huge amount of amino acids in order to influence evolution (if that is possible at all) single organisms could be sufficient under suitable conditions. That could make up for their lower stability. Thus I wouldn’t limit panspermia to amino acids only.

Too high-tech.

There is no high-tech required. Simple bioreactors have already been used thousands of years ago (e.g. brewing kettles). I would even say that is a prim example for low-tech.

How badly does water limit radio? Assuming the same power output, is a radio signal in water significantly affected more than in air?

Yes, it is. That’s why remotely operated underwater vehicles are cable controlled. It would be impossible to do that with radio waves due to the damping in water.

Because a little bit of light reading puts an upper limit of the size of terrestrial ocean worlds. Not much bigger than Enceladus.

There are different opinions. According to Li Zeng et.al. water worlds are most likely in the range of 2-4 R_⊕. That would mean that your planet is rather too small (if the known exoplanets would be representative).

 

[stefan r]

RNA and DNA are quite likely to emerge on other planets. Within our own metabolism the basic sugars are frequently exchanged. There is no reason an alien metabolisms would miss ribose and deoxyribose while they are evolving. Phosphate would be the same too.

What is very likely to be radically different is the coding. Our DNA uses 3 base pairs (64 options) to code for 21 amino acids. The aliens can use different molecules as a base pair. An extra set of unnatural base pairs would allow for base six coding. They could also use binary code instead of base 4. Regardless even if it is base 4 and the nucleotides are ATCG like on Earth there is no reason for the code guanine-guanine-guanine to code for the amino acid glysine.

The aliens may not use the same 20 basic amino acids. Creatures on Earth use lots of amino acids that are not directly coded for in DNA. I think you would need a supplement to cover amino acids that are more rare. The increased concentration of non-standard amino acids might strain metabolism. The human liver can break up any protein into amino acids. In most cases we do not do that. I think your main concern for poison is times when the molecule looks like a known strand of protein but functions in a slightly different way.

The left handed orientation vs right handed orientation would cause a long series of metabolic difficulty. This is probably a 50-50 chance. It is likely that the entire ecosystem follows the same orientation. For writing a story take your pick. Either everything can be poisonous because of chiral molecules that need to be broken down or nearly nothing is poisonous in this way.

Branched hydrocarbons and trans-fats are difficult for human metabolism. Some organisms on Earth take advantage of this. It is likely to be rare. The branched hydrocarbons and trans-fats are a reason that your colonists shouldn't over-process their food. Some people do this on Earth today and it only cuts life expectancy by a few decades.

You are in a science fiction world. You could have a back pack sized device containing bacteria that digest wood pulp and leaves. This device might extract the products directly giving you giving you a supply of oil similar to canola or carbs like high-fructose corn syrup. That could be eaten directly by your colonists or it could be fed to nearly natural Earth organisms like insect larvae.