Chlorophyliac humans, binary stars and boiling oceans

[gestaltist]

I have some additional ideas but I would like to check for your feedback on the above first.

Personally, I think in this case less in more. The more things this fungus does, the more it becomes like any other speculative-fiction superpower. Allowing photosynthesis in human-like creatures? Sure. It's interesting, and allows for interesting speculation on how they would differ from normal humans. Add immunity to toxins, enhanced metabolism, EM detection, and objective emotional sense? It's gone into magic-handwavy territory that strains credibility.

Yeah, you might be right. Under the influence of the various comments that there is no chance of effective photosynthesis in humans I was trying to add some additional benefits of the fungus that would make it more explainable why it is so effective (the metabolism and toxin thing).

What would you say if I do it like this: due to the evolutional differences, some stuff that is toxic for humans is not toxic for the Porphyroi, and vice versa. I kinda have an idea for a misunderstanding when the two species meet each other, and one of them gets accidentally poisoned while being invited to a meal.

Regarding emotional sense - yeah, I might have gone too Avatar-heavy with that one. The thing is, I would like to have some „trace of magic“ in that world that isn’t strictly magic. Would it be less jarring if it is a rare ability? I.e., let’s say, one in a few thousand Porphyroi has it.

I won't comment much on the time scale - it seems far too short for me, especially for cellular-level incorporation, but I'm not knowledgeable enough except to point to chloroplasts' and mitochondria's billion-plus years - but the fungus infecting multiple species seems odd. What are the chances multiple species, encompassing highly divergent groups, all have the same immunodeficiencies that let the fungus infest the host, and (presumably) all gain use of its photosynthesis?

I’m not gonna argue because my knowledge of biology and genetics is much worse than I would like it to be. I thought that if a fungus was that beneficial, it would try and infect everything - but you might be right that it makes more sense to have it integrate with one species only. I am fine either way.

And one final comment, I'm of the opinion that leaving things unexplained is better than handwaving them poorly. If you say photosynthesis can be enhanced through the Earth's EM field, I'd expect you to be able to back that up with details, given how much we know about photosynthesis and the EM field. If you just say they photosynthesize more efficiently than chloroplasts, it satisfies curiosity without trapping you in something you ultimately handwave anyways (assuming that the EM field bit is just a bit of attempted explanation, without any real scientific basis).

Fair enough. The EM field was partly a bit of attempted explanation, but also, as I mentioned above, an attempt to add a little bit of „magic“ to the world. In hindsight, it is very sketchy.

[Lambuzhao]

I won't comment much on the time scale - it seems far too short for me, especially for cellular-level incorporation, but I'm not knowledgeable enough except to point to chloroplasts' and mitochondria's billion-plus years - but the fungus infecting multiple species seems odd. What are the chances multiple species, encompassing highly divergent groups, all have the same immunodeficiencies that let the fungus infest the host, and (presumably) all gain use of its photosynthesis?

I would think that the porphyroplasts would have long been incorporated at the early eukaryotic stage in evolution. It would have had the chance to be exhibited in certain species, while dying out in others.

Also, it seems that the evolutionary incorporation of chloroplasts especially, may well have been a multiple event. 1 billion years is a long, long time for Life to try to get the symbiotic thing right.

[gestaltist]

I won't comment much on the time scale - it seems far too short for me, especially for cellular-level incorporation, but I'm not knowledgeable enough except to point to chloroplasts' and mitochondria's billion-plus years - but the fungus infecting multiple species seems odd. What are the chances multiple species, encompassing highly divergent groups, all have the same immunodeficiencies that let the fungus infest the host, and (presumably) all gain use of its photosynthesis?

I would think that the porphyroplasts would have long been incorporated at the early eukaryotic stage in evolution. It would have had the chance to be exhibited in certain species, while dying out in others.

Also, it seems that the evolutionary incorporation of chloroplasts especially, may well have been a multiple event. 1 billion years is a long, long time for Life to try to get the symbiotic thing right.

That’s an intreaguing thought. This way, there could be multiple species with porphyroplasts in various regions of the world. I imagine that Ice Ages, big volcanic events, etc, are good candidates for that feature dying out in most species.

[Lambuzhao]

It absolutely DOES NOT have to be some catastrophic event.
It could simply be that, in some species/phyla/kingdoms of life, the porphyroplasts became more and more useless (i.e. they ceased providing secondary/tertiary nutrient efficiently,ceased antitoxin absorption, ... any number of reasons). That's the good thing about having this sort of intracellular adoption take place over the course of millennia.
It can be selected to remain in some species, but then phase out in other species.

Nonetheless, they might have traded up their function into something convergent on the mitochondria (?), or perhaps a variety of porphyroplast became the mitochondria in non-photosynthesizing mauve organisms.

[gestaltist]

It absolutely DOES NOT have to be some catastrophic event.
It could simply be that, in some species/phyla/kingdoms of life, the porphyroplasts became more and more useless (i.e. they ceased providing secondary/tertiary nutrient efficiently,ceased antitoxin absorption, ... any number of reasons). That's the good thing about having this sort of intracellular adoption take place over the course of millennia.
It can be selected to remain in some species, but then phase out in other species.

Nonetheless, they might have traded up their function into something convergent on the mitochondria (?), or perhaps a variety of porphyroplast became the mitochondria in non-photosynthesizing mauve organisms.

Sounds intriguing and daunting at the same time. Do you have any tips on creating interesting flora and fauna for a conworld while maintaining familiarity?

[gestaltist]

I’ve decided to drop the whole EM vision from the porphyroi, and to have several animal orders with varying degrees of photosynthesis (based on Lambuzhao’s argument). The „porphyrins“ got integrated into cells of most animals at a very early stage, but got discarded from most due to their marginal utility. They got preserved and enhanced in some species of various orders, including the Porphyroi.

I would still like to have the EM vision, but would like to defer it to another species. What do you guys think:

An order of mostly carnivorous small mammals undergoes a mutation of the porphyrins so that they stop being photosynthetic, but feed information about EM and heat signatures into their nervous systems. As a result, they get a kind of „infrared sense“ and get very good at being night-time hunters.

One species evolves to be bigger, more intelligent, and ultimately sentient. They are able to sense the „auras“ of nearby beings (EM and heat signatures), and to manipulate their own aura to some extent, so it becomes a means of communication. Their sight is poor because it is less important. My codename for them is the „auropaths“.

[Lambuzhao]

Sounds intriguing and daunting at the same time. Do you have any tips on creating interesting flora and fauna for a conworld while maintaining familiarity?

I don't know how realistic "familiarity" ought to be, but to things leaped to mind when I read your query:

1) The Cambrian Explosion
http://en.wikipedia.org/wiki/Cambrian_explosion

2) Furahan Biology BlogSpot
http://planetfuraha.blogspot.com/2009/0 ... gy-is.html


3) the flora and fauna ideas of Brian Froud in The World of the Dark Crystal

4) Nemo Ramjet & the alien para-tetrapods of Snaiad
http://scienceblogs.com/tetrapodzoology ... of-snaiad/
{sadly, I believe that snaiad.com is offline (?!?). }

(or, just type Snaiad in Google Images. Have plenty of tissues for copious tears of cosmopoetic joy/conworldly drool.


5) Dougal Dixon's Green World
{IMHO a kind of weak-sister copy of Nemo Ramjet's stuff (and I am an every-Sunday acolyte to D. Dixon's para-evolutionary romps), but some shiny nuggets there}

I'm sure there are plenty more options out amongst the Intertoobs. With a little sifting, who knows what you'll find...

[gestaltist]

These are some very good links, thanks Lambuzhao. My favorite part of conworlding is learning about stuff.

I am afraid that I will feel compelled to do some sort of elaborate conbiology at this point, and it will take me a lot of time to get this world to a coherent state.

I have already started playing with various evolutionary pathways and have invented a bunch of species of fish, birds, reptiles and therapsids. It’s a lot of fun.

My only worry is that this world will have a high barrier to entry because of the amounts of unfamiliar stuff. It’s not easy to get the balance right between realism and familiarity.

[Imralu]

Chlorophyll only won on Earth because green is the color that the sun emits very strongly but yet gets through to shallow water bottoms the best, which is where the first plants evidently grew up.

Also, regarding purple chloroplasts - why the heck not? Another liquid that permits purple/ultraviolet wavelengths to admit to shallow depths, while reflecting/refracting other wavelengths, would be all you needed. I don't know of any such contenders, though.

Uh, guys? Chlorophyll doesn't absorb green light the best. It looks green precisely because green is the wavelength it is the worst at absorbing. Purple photosynthesising compounds are going to be worst at absorbing purple light.

Both green and purple are perfectly fine as photosynthesisers although I don't know details of their efficiency and what chemicals they run on and produce as byproducts. I heard once a fairly wild but possible sounding theory that purple was actually the dominant colour of photosynthesants which lived at the surface of the water and green was what worked best in the filtered purple light underneath and it just so happened that the green photosynthesants were the ones to be incorporated into cells and become the ancestors of chloroplasts.

An extreme axial tilt like Uranus'? Of course, that will warm up the poles but freeze the equator, so...

I have though a problem with the tilt of your planet. With that tilt, you would have a burning pole, a freezing pole and a temperate equator. The whole thing with a weird atmospheric circulation that tries to get the heat from the hot pole to the frozen one.

Salmoneus beat me to it, but I just wanted to point out that gyroscopes are a thing, the Earth has seasons and Uranus doesn't roll around the sun. A planet with a strong axial tilt will point one of its poles towards its star when it's on one side of its orbit and the other pole towards the star on the other side.

[Lambuzhao]

Uh, guys? Chlorophyll doesn't absorb green light the best. It looks green precisely because green is the wavelength it is the worst at absorbing. Purple photosynthesising compounds are going to be worst at absorbing purple light.

Woops! Thanks, Imralu. Indeed, chlorophyll absorbs mostly red & blue wavelengths, while porphyrioplasts would absorb mainly light green to red/infrared wavelengths.

Still, I humbly offer this in partial defense-

http://www.bio.net/bionet/mm/plant-ed/1 ... 01134.html

I hope that isn't complete poppycock.

[Lambuzhao]

These are some very good links, thanks Lambuzhao. My favorite part of conworlding is learning about stuff.

I am afraid that I will feel compelled to do some sort of elaborate conbiology at this point, and it will take me a lot of time to get this world to a coherent state.

I have already started playing with various evolutionary pathways and have invented a bunch of species of fish, birds, reptiles and therapsids. It’s a lot of fun.

My only worry is that this world will have a high barrier to entry because of the amounts of unfamiliar stuff. It’s not easy to get the balance right between realism and familiarity.

Really, that's up to you. The harder the science in scifi, the less of a chance of torrid interspecies love-scenes. Well, at least ones that look remotely human.
Same goes for rampant interspecies love-children. But really, in the grand scheme of things, there are more things in heaven and earth than are dreamt of in our playful dance.

[gestaltist]

These are some very good links, thanks Lambuzhao. My favorite part of conworlding is learning about stuff.

I am afraid that I will feel compelled to do some sort of elaborate conbiology at this point, and it will take me a lot of time to get this world to a coherent state.

I have already started playing with various evolutionary pathways and have invented a bunch of species of fish, birds, reptiles and therapsids. It’s a lot of fun.

My only worry is that this world will have a high barrier to entry because of the amounts of unfamiliar stuff. It’s not easy to get the balance right between realism and familiarity.

Really, that's up to you. The harder the science in scifi, the less of a chance of torrid interspecies love-scenes. Well, at least ones that look remotely human.
Same goes for rampant interspecies love-children. But really, in the grand scheme of things, there are more things in heaven and earth than are dreamt of in our playful dance.

Did you maybe quote the wrong post? I don’t see the connection between your answer and what you quoted...

[gestaltist]

The work on my conworld is progressing nicely and I would like to share with you what I have so far, as you have helped me a lot in defining stuff. This will only be an excerpt of what I have, as not to bore you with too much detail.

Cosmology

The solar system consists of two twin stars of type G8 with about 0.7 the solar luminosity each, orbiting a common barycenter with a period of 13.3 Earth days (or exactly 14 days on my planet).

The planet orbits the suns with a semi-major axis of 1.155 AU. The planet’s radius is 7650 km (about 20% more than the Earth). The gravity is Earth-like. The planet’s rotation is about 26% faster than the Earth’s, making the day somewhat shorter than on Earth (about 5% shorter). The planet’s orbital period is exactly 364 days.

There are two moons: one „Earth-like“ with a synodic period of 35.9 days and a more distant one with a synodic period of 70.5 days. The apparent size of the bigger one is still only 0.6 of any of the stars, so there are no true solar eclipses. The distant one is highly reflective and reddish - although it’s apparent size is only a tenth of the Earth’s moon, it is bright enough during full moon to be a notable event.

Evolution

The general evolutionary tree is Earth-like. I don’t want my world to be too weird and alien. There are two most notable differences:

1) the early lobe-finned fish (the ancestors of all land-based animals) have developed additional light-sensitive mitochondria that went on to accept a variety of roles in the later species: from (rare) photosynthetic abilities to helping animals orient themselves in the jungle (making it easier to sense where the suns are through the foliage) to sensing other animals thermal signatures (common in predators). Of course, they have atrophied in a lot of species.

2) the therapsids haven’t died out and are thriving - most of them relatively mammal-like (warm-blooded, have fur) but oviparous.

Sentient species

The Old Race - a few hundred thousand years before humans, a sentient species of therapsids (of the clade of Eutheriodontia) evolved from a family of jungle-based facultative carnivores that used their light-sensitive mitochondria to sense thermal signatures of their prey.

The Auropaths, as I call them, are somewhat smaller than humans, are covered in short fur, have muzzles and tails. The thermal sensitivity has evolved to a next level: they have evolved to be able to precisely interpret internal states of their own species and other species on their continent, giving them a means of communication and an affinity for taming and domesticating animals. (I am still not sure if I want to give them any form of sound-based language: my alternative is for them to communicate via changing the thermal signatures of their faces.)

They have become herders and have spread far out of their original habitat in the Southern hemisphere, but it took them a very long time to start to develop tools, and a longer time still to become sedentary (due to their higher reliance on meat).

Finally, one part of them that migrated to the Northern hemisphere, has managed to create the first civilization in the history of the planet. It survived a long time, until a cataclysm put an end to it, leaving only scattered chiefdoms in the northern hemisphere.

The humans used the opportunity to expand. (Proto-)humans evolved with the light-sensitive mitochondria, as well: their ape ancestors used them to better orient themselves in the jungle. On the savanna, the photosynthetic ability started to appear. The humans spread all across the Northern hemisphere, eradicating the rest of the Auropaths they found. They have been pushed back from the jungles, though, and the Southern hemisphere remained firmly in the hands of the Old Race.

After that, a long Ice Age began. The light-sensitive mitochondria atrophied in most humans, remaining as a vestigial trait of some races having orange- or reddish-hued skin. Also, the humans on this planet have a far greater ability to change their skin color to adjust for the season: so they can be dark-brown in the summer but pale-white in the winter.

There was one group of (proto)humans that moved to a tropical archipelago during the Ice Age’s lower sea levels. Separated from the rest of their species, and living in a very different climate, their evolution took a different spin.

The Porphyroi - evolving on the sunny beaches of their archipelago, managed to maintain and expand their photosynthetic abilities. Their skin learned to absorb water in which they waded hunting for fish, and to use it in photosynthesis. Since they were the main topic of this thread, I will spend some more time on describing them:

Physical appearance - their skin is purple because of the sun-sensitive porphyrins. They have special subcutaneous tissue that can store water for use in photosynthesis - they need to spend at least 15 minutes a day in the water or their skin becomes dry and wrinkled and their photosynthetic ability stops being effective. Optimally, they should spend about an hour a day in the water. They can also accept more water (giving them a somewhat puffy appearance) if they need to prepare for a longer time away from it. They have evolved to be able to filter out the salt from the sea water and can use it just as effectively.

Their noses are flat and can be closed at will which helps in diving. It also gives them an additional mode of articulation: with the nose closed (try speaking with your nose pinched for an impression).

Their eyes are adjusted to seeing underwater.

The skin between their fingers is somewhat loose, and their feet more loosely structured. They can be spanned (which gives them a frog-like appearance) to aid them in swimming.

Civilizations

The Porphyroi only need half as much food as humans, the rest being supplied by photosynthesis. Their early societies concentrated around lakes, big rivers and ocean beaches. They hunted for fish and ate plants that grew near the water (domesticating rice and sugar cane pretty quickly).

Their rapid population growth forced more and more people to areas less rich in water. They quickly learned to build dams and irrigated terraces to create environments that allowed them to spend enough time in the water. These changes made it necessary to develop more structured governments and thus gave them an advantage - the inhabitants of these secondary habitats ended up conquering the rest of the Porphyroi.


OK - this has become really long. I have a lot more stuff in the works but I think this is enough to give you guys a taste.

[Zaarin]

The work on my conworld is progressing nicely and I would like to share with you what I have so far, as you have helped me a lot in defining stuff. This will only be an excerpt of what I have, as not to bore you with too much detail.

Cosmology

The solar system consists of two twin stars of type G8 with about 0.7 the solar luminosity each, orbiting a common barycenter with a period of 13.3 Earth days (or exactly 14 days on my planet).

The planet orbits the suns with a semi-major axis of 1.155 AU. The planet’s radius is 7650 km (about 20% more than the Earth). The gravity is Earth-like. The planet’s rotation is about 26% faster than the Earth’s, making the day somewhat shorter than on Earth (about 5% shorter). The planet’s orbital period is exactly 364 days.

There are two moons: one „Earth-like“ with a synodic period of 35.9 days and a more distant one with a synodic period of 70.5 days. The apparent size of the bigger one is still only 0.6 of any of the stars, so there are no true solar eclipses. The distant one is highly reflective and reddish - although it’s apparent size is only a tenth of the Earth’s moon, it is bright enough during full moon to be a notable event.

Sounds good for the most part. A couple questions or observations:
1) Larger planet + equivalent gravity = lower density; lower density likely = lower metal content. Just something to be aware of.
2) How do you account for the red moon's high albedo? Rock usually has a rather low albedo compared to volatiles or metals. Mars, for example, has only a very slightly higher albedo than the Moon. If the red moon's mass is high enough, however, it could hypothetically be a Titan-like moon with a reddish atmosphere, which would be significantly brighter than Mars or the Moon (cf. Venus).

Evolution

Biology isn't really my strong subject compared to anthropology and astronomy, so no comment beyond seems plausible.

Sentient species

Interesting stuff. Only comment is that (semi-)webbed hands might make fine articulation of tools difficult.

[gestaltist]

1) Larger planet + equivalent gravity = lower density; lower density likely = lower metal content. Just something to be aware of.

Yes, I know that. This is going to be a low-tech world so I don’t need tons of metal for an industrial civilization.

2) How do you account for the red moon's high albedo? Rock usually has a rather low albedo compared to volatiles or metals. Mars, for example, has only a very slightly higher albedo than the Moon. If the red moon's mass is high enough, however, it could hypothetically be a Titan-like moon with a reddish atmosphere, which would be significantly brighter than Mars or the Moon (cf. Venus).

Ice contaminated with some kind of red pulverized rock was my idea. Would that work?

Interesting stuff. Only comment is that (semi-)webbed hands might make fine articulation of tools difficult.

Good point. As I imagine it, the hands in their „off“ state don’t look too different from human hands. They are like hands with a little wrinkled tissue between the fingers. They don’t need to be fully webbed anyway. My main thought was that a species living mostly near the water would greatly benefit from a means to flee from predators like crocodiles.

Also - thanks for taking the time to read this.

[Zaarin]

2) How do you account for the red moon's high albedo? Rock usually has a rather low albedo compared to volatiles or metals. Mars, for example, has only a very slightly higher albedo than the Moon. If the red moon's mass is high enough, however, it could hypothetically be a Titan-like moon with a reddish atmosphere, which would be significantly brighter than Mars or the Moon (cf. Venus).

Ice contaminated with some kind of red pulverized rock was my idea. Would that work?

As a source of redness, sure. Such a body exists in our solar system: Sedna. It's albedo is only half that of Venus, but three times that of the Moon or Mars. Most Trans-Neptunian Objects are quite red due to hydrocarbons and tholins; something similar could color your red moon. Sedna is the reddest object in the Solar System, even redder than Mars. Pluto is also reddish, similar to Jupiter's moon Io; both have an albedo similar to Venus, presenting another possibility.

The chief problem is the ice from an icy moon would probably sublime in the sunlight in the habitable zone. This would a) uncover fresh bright white ice and b) eventually result in no ice and a plain rocky core. I once posited an icy moon in a system's habitable zone, but the ice sublimed in daylight and refroze at night, creating a glassy surface and, on a cosmological scale, an ephemeral moon. There is water frozen in craters on the Moon and Mercury in places that never see sunlight, but that doesn't help an entire moon. The only solution I can think of would be to make the moon have a really bizarre orbit that always keeps the planet between it and the sun, but I can't think of any natural way such an orbital resonance would develop. That also means a moon illuminated only by earthshine.

A more likely solution would be to give it red tinged clouds, which would give it a high albedo similar to Venus, Jupiter, and Saturn. Phosphorus, sulfur, and hydrocarbons are all likely candidates; someone with more knowledge of chemistry might suggest other alternatives as well. Note that Titan is smaller than Ganymede and less massive than Mercury, neither of which have atmospheres, suggesting more than simply mass is involved in the acquisition of an atmosphere by a moon (though the reason for Mercury's lack of atmosphere is obviously its proximity to the sun). Since the origin of Titan's atmosphere is unclear (especially in light of the lack of such an atmosphere on Ganymede and Callisto), you can probably be fairly hand-wavy about it.

Also - thanks for taking the time to read this.

Yep.

[gestaltist]

As a source of redness, sure. Such a body exists in our solar system: Sedna. It's albedo is only half that of Venus, but three times that of the Moon or Mars. Most Trans-Neptunian Objects are quite red due to hydrocarbons and tholins; something similar could color your red moon. Sedna is the reddest object in the Solar System, even redder than Mars. Pluto is also reddish, similar to Jupiter's moon Io; both have an albedo similar to Venus, presenting another possibility.

The chief problem is the ice from an icy moon would probably sublime in the sunlight in the habitable zone. This would a) uncover fresh bright white ice and b) eventually result in no ice and a plain rocky core. I once posited an icy moon in a system's habitable zone, but the ice sublimed in daylight and refroze at night, creating a glassy surface and, on a cosmological scale, an ephemeral moon. There is water frozen in craters on the Moon and Mercury in places that never see sunlight, but that doesn't help an entire moon. The only solution I can think of would be to make the moon have a really bizarre orbit that always keeps the planet between it and the sun, but I can't think of any natural way such an orbital resonance would develop. That also means a moon illuminated only by earthshine.

A more likely solution would be to give it red tinged clouds, which would give it a high albedo similar to Venus, Jupiter, and Saturn. Phosphorus, sulfur, and hydrocarbons are all likely candidates; someone with more knowledge of chemistry might suggest other alternatives as well. Note that Titan is smaller than Ganymede and less massive than Mercury, neither of which have atmospheres, suggesting more than simply mass is involved in the acquisition of an atmosphere by a moon (though the reason for Mercury's lack of atmosphere is obviously its proximity to the sun). Since the origin of Titan's atmosphere is unclear (especially in light of the lack of such an atmosphere on Ganymede and Callisto), you can probably be fairly hand-wavy about it.

Thanks for the advice. I have added the second moon at the last moment, so it isn’t as well thought out as the rest. It is supposed to have a pretty normal orbit with low eccentricity. It’s radius is 689 km and mass is 17.198 x 10^22 kg. Is that enough to sustain an atmosphere? The role of this moon is to add a notable celestial event every 70 days or so (as the observed brightness grows disproportionately during full moon, this is the only time when non-astronomers would be able to easily see the moon).

Also, one thing I am having trouble with - do you have an idea how I could calculate the times of solar and lunar eclipses? My system is somewhat complicated in that regard: there are two stars, two moons, even the larger moon would never cover a star completely, etc.

One thing I am wondering about: would I only have lunar eclipses when one of the stars eclipses the other? Or would the system behave like it had only one star because of the distance of the suns?

[Zaarin]

As a source of redness, sure. Such a body exists in our solar system: Sedna. It's albedo is only half that of Venus, but three times that of the Moon or Mars. Most Trans-Neptunian Objects are quite red due to hydrocarbons and tholins; something similar could color your red moon. Sedna is the reddest object in the Solar System, even redder than Mars. Pluto is also reddish, similar to Jupiter's moon Io; both have an albedo similar to Venus, presenting another possibility.

The chief problem is the ice from an icy moon would probably sublime in the sunlight in the habitable zone. This would a) uncover fresh bright white ice and b) eventually result in no ice and a plain rocky core. I once posited an icy moon in a system's habitable zone, but the ice sublimed in daylight and refroze at night, creating a glassy surface and, on a cosmological scale, an ephemeral moon. There is water frozen in craters on the Moon and Mercury in places that never see sunlight, but that doesn't help an entire moon. The only solution I can think of would be to make the moon have a really bizarre orbit that always keeps the planet between it and the sun, but I can't think of any natural way such an orbital resonance would develop. That also means a moon illuminated only by earthshine.

A more likely solution would be to give it red tinged clouds, which would give it a high albedo similar to Venus, Jupiter, and Saturn. Phosphorus, sulfur, and hydrocarbons are all likely candidates; someone with more knowledge of chemistry might suggest other alternatives as well. Note that Titan is smaller than Ganymede and less massive than Mercury, neither of which have atmospheres, suggesting more than simply mass is involved in the acquisition of an atmosphere by a moon (though the reason for Mercury's lack of atmosphere is obviously its proximity to the sun). Since the origin of Titan's atmosphere is unclear (especially in light of the lack of such an atmosphere on Ganymede and Callisto), you can probably be fairly hand-wavy about it.

Thanks for the advice. I have added the second moon at the last moment, so it isn’t as well thought out as the rest. It is supposed to have a pretty normal orbit with low eccentricity. It’s radius is 689 km and mass is 17.198 x 10^22 kg. Is that enough to sustain an atmosphere? The role of this moon is to add a notable celestial event every 70 days or so (as the observed brightness grows disproportionately during full moon, this is the only time when non-astronomers would be able to easily see the moon).

Also, one thing I am having trouble with - do you have an idea how I could calculate the times of solar and lunar eclipses? My system is somewhat complicated in that regard: there are two stars, two moons, even the larger moon would never cover a star completely, etc.

One thing I am wondering about: would I only have lunar eclipses when one of the stars eclipses the other? Or would the system behave like it had only one star because of the distance of the suns?

If you don't need a bright moon, just cover it in iron oxide dust like Mars, which is slightly brighter than the Moon anyway. I doubt such a small moon could maintain an atmosphere.

Based on what you described, I think you'd have transits rather than eclipses. I'm sure there are formulae for calculating eclipses, transits, and occultations, but math isn't my strongsuit. I'd probably use something like Astrosynthesis (a good program for setting up systems anyway) to visualize it. As for the stars, it sounds like they are separated pretty narrowly; I imagine their combined glare would make them appear as a single object in the sky except during partial eclipses (assuming the moon covers enough of the sun disk to make the corona distinct). I could be wrong about that, though. Either way, they would appear very close together in the sky; no Tattooine-esque sunsets.

[gestaltist]

If you don't need a bright moon, just cover it in iron oxide dust like Mars, which is slightly brighter than the Moon anyway. I doubt such a small moon could maintain an atmosphere.

Thanks. I will go with the iron oxide.

Based on what you described, I think you'd have transits rather than eclipses. I'm sure there are formulae for calculating eclipses, transits, and occultations, but math isn't my strongsuit. I'd probably use something like Astrosynthesis (a good program for setting up systems anyway) to visualize it. As for the stars, it sounds like they are separated pretty narrowly; I imagine their combined glare would make them appear as a single object in the sky except during partial eclipses (assuming the moon covers enough of the sun disk to make the corona distinct). I could be wrong about that, though. Either way, they would appear very close together in the sky; no Tattooine-esque sunsets.

It is surprisingly difficult to find good mathematical models for calculating these things online. Astrosynthesis isn’t an option for me, unfortunately, as I am a Mac user. I will probably end up writing a script to calculate these.

[gestaltist]

As for the stars, it sounds like they are separated pretty narrowly; I imagine their combined glare would make them appear as a single object in the sky except during partial eclipses (assuming the moon covers enough of the sun disk to make the corona distinct). I could be wrong about that, though. Either way, they would appear very close together in the sky; no Tattooine-esque sunsets.

I’ve been meaning to ask about this.

The stars’ distance from one another equals 14 times their diameter. So it seems to me that they would be rather distinct on the sky: wouldn’t they look like you could fit 14 suns between them? Of course, this is at their most distant, which would occur once every seven days.

[Zaarin]

As for the stars, it sounds like they are separated pretty narrowly; I imagine their combined glare would make them appear as a single object in the sky except during partial eclipses (assuming the moon covers enough of the sun disk to make the corona distinct). I could be wrong about that, though. Either way, they would appear very close together in the sky; no Tattooine-esque sunsets.

I’ve been meaning to ask about this.

The stars’ distance from one another equals 14 times their diameter. So it seems to me that they would be rather distinct on the sky: wouldn’t they look like you could fit 14 suns between them? Of course, this is at their most distant, which would occur once every seven days.

Bear in mind that because of the glare we do not see the sun disk proper. With a period of 13.3 days, I would suspect that the glare of the two suns would merge and they would appear as an oblong shape in the sky (becoming an eclipsing binary with a period of 14 days as you said). They would probably only be separable during a partial eclipse and perhaps sunset, though they would probably set together since they would almost certainly orbit each other with their equators perpendicular to the ecliptic, making them appear side-by-side in the sky (unless the planet has an unusual inclination; note that this is not the case for any of the major planets in our solar system--the terrestrial planets have negligible inclinations).

[gestaltist]

Bear in mind that because of the glare we do not see the sun disk proper. With a period of 13.3 days, I would suspect that the glare of the two suns would merge and they would appear as an oblong shape in the sky (becoming an eclipsing binary with a period of 14 days as you said).

Hmm, I don’t like this at all. In my mind, there need to be two Suns in the sky. What distance would I need for stars of this luminosity so that they appear as separate objects most of the time? I don’t mind expanding their orbit somewhat. I’d rather I didn’t have to change other parameters...

[Zaarin]

Bear in mind that because of the glare we do not see the sun disk proper. With a period of 13.3 days, I would suspect that the glare of the two suns would merge and they would appear as an oblong shape in the sky (becoming an eclipsing binary with a period of 14 days as you said).

Hmm, I don’t like this at all. In my mind, there need to be two Suns in the sky. What distance would I need for stars of this luminosity so that they appear as separate objects most of the time? I don’t mind expanding their orbit somewhat. I’d rather I didn’t have to change other parameters...

You're now getting into a lot of math which, as I said, is not my strong suit. As it stands, I believe your suns would more or less look like lobes at aphelion/perihelion and more or less like our own sun at opposition. If you want distinct suns, you want a separation of at least several degrees--cf. Mercury, at ~0.4 AU and a maximum separation from the sun of 28° and is still difficult to separate from the sun most of the time. For two stars, I would guess that 0.4 AU would still allow them to be tidally locked to each other, but you also might want to move out your planets' orbits just a tiny bit.

ETA: Unless the period of the suns is identical to the year of the planet, they will unavoidably be eclipsing binaries from the perspective of the people on the planet, eclipsing each other with a period half that of the suns' (i.e., twice a solar year). Which will have interesting implications for the people; no Ptolemaic theories of the perfection and immutability of the superlunary spheres...

[gestaltist]

As it stands, I believe your suns would more or less look like lobes at aphelion/perihelion and more or less like our own sun at opposition. If you want distinct suns, you want a separation of at least several degrees--cf.

Do you know of any online source where I could educate myself on the way the Sun is perceived from the Earth? For me, optics is not a strong suit of mine...

Mercury, at ~0.4 AU and a maximum separation from the sun of 28° and is still difficult to separate from the sun most of the time. For two stars, I would guess that 0.4 AU would still allow them to be tidally locked to each other, but you also might want to move out your planets' orbits just a tiny bit.

Mercury is very small compared to the Sun, though... I think I need to really understand the optics at work here before I change anything. And I am afraid I don’t even know where to start...

ETA: Unless the period of the suns is identical to the year of the planet, they will unavoidably be eclipsing binaries from the perspective of the people on the planet, eclipsing each other with a period half that of the suns' (i.e., twice a solar year). Which will have interesting implications for the people; no Ptolemaic theories of the perfection and immutability of the superlunary spheres...

That’s actually a part of what I have in mind: a „week“ for the people of this planet was supposed to be the seven days between the two solar eclipses.

And playing with the implications of this for mythology and science is currently my favorite pastime.

[Zaarin]

If you don't mind being a little hand-wavy, I think you could get away with giving the two suns a few degrees of separation; they're still going to be close, but they could at least be visible as separate sun disks.

Re:optics, I admit that I'm less secure in the optics department than in the astrophysics department. You could start on the Wikipedia page which includes some formulae for calculating size in arcminutes.