science of 'the expanse'

[tantric]

kudos to 'the expanse' for putting the science back in science fiction, but a few things bug me...

ceres has a surface g of .03. it's been spun up to have spin g of .3. now, setting aside how much energy that would take, when the spin g exceeds natural g by an order of magnitude, wouldn''t it just fly apart?

ganymede as the breadbasket of the outer system - wtf? plants don't need soil to grow, not that there's soil on ganymede, they need light. you could grow them on any old asteroid. ganymede is deep in jupiter's gravity well and lethal radiation field. mirrors? reflecting what? they have cheap fusion, what's the problem with lighting?

[factotum]

ceres has a surface g of .03. it's been spun up to have spin g of .3. now, setting aside how much energy that would take, when the spin g exceeds natural g by an order of magnitude, wouldn''t it just fly apart?

ganymede as the breadbasket of the outer system - wtf? plants don't need soil to grow, not that there's soil on ganymede, they need light. you could grow them on any old asteroid. ganymede is deep in jupiter's gravity well and lethal radiation field. mirrors? reflecting what? they have cheap fusion, what's the problem with lighting?

First one: it depends entirely on what the tensile strength of the material making up Ceres is, and also what sort of reinforcements they added to it before spinning it up--I don't know enough about the show to know how that works out (since, for some reason, it's only available on Netflix in the UK and I don't have a subscription).

Ganymede: Jupiter doesn't have a lethal radiation field? In fact, its magnetosphere deflects solar radiation, and since Ganymede is well inside that magnetosphere it will be suffering rather *less* radiation than a random rock in deep space would. Mirrors would presumably be reflecting sunlight, which still exists even as far as out as Jupiter, and even if you have cheap fusion, it's cheaper still to use the permanently-burning fusion reactor at the centre of our solar system.

[erikun]

ceres has a surface g of .03. it's been spun up to have spin g of .3.

...say what?

Gravity on a physical object behaves (or is believed to behave) based on the curvature of spacetime, due to the mass of the object. If you wish to increase the gravity, what is required is adding mass to the object. Spinning it is not going to produce more gravity on the surface.

The idea behind spinning something to produce "gravity" involves an object like an O'Neill cylinder, which is a hollowed-out tube which rotates fast enough to pull objects towards the outer edges, thus simulating gravity with rotational forces. This would not "increase" the gravity of a Ceres-mass object, and arguably needs to work against the internal gravity by mass because the artificial gravity, created by rotation, works against the gravity attempting to pull the entire assembly towards its center.

ganymede as the breadbasket of the outer system - wtf? plants don't need soil to grow, not that there's soil on ganymede, they need light. you could grow them on any old asteroid. ganymede is deep in jupiter's gravity well and lethal radiation field. mirrors? reflecting what? they have cheap fusion, what's the problem with lighting?

Plants might not "need" soil to grow, but it is certainly more useful. And depending on the situation, it might be easier just to throw down some soil rather than trying to manufacture the required nutrient and chemical balance and running it through a water supply.

The reason why you might want to use light from the sun rather than manufactured light is that the sun already produces light in the full spectrum. Manufactured light is only going to produce light in the wavelengths giving off by the burning or heated material, which might not turn out as efficient. Plus, as factotum noted, it can be far less energy-intensive to establish a set of mirrors in an established orbit rather than continuing to produce electricity and/or burnable materials for a generated light source.

I am not sure that plants grow any better in microgravity than humans. Although, honestly, it isn't exactly something that has been studied well.

I would honestly have a bigger problem with the energy expenditure required to pull food out of Jupiter's gravity well, more than anything else. That has to be considerable, especially if it is something done on a continuous or regular basis. That is likely the biggest problem with the idea of placing your food source right next to Jupiter.

[HandofShadows]

I think the key term here is "outer system". Ganymede being the breadbasket is likely the result of a lot of different factors ranging from trade routes to local economic factors to environment.

[tantric]

the surface of ganymede receives about 8 rem/day. it takes ~100rem in a short period to cause acute radiation poisoning.

the fine material on the surface of ganymede (and mars) isn't soil - far from it. it's regolith. the best you could hope to find is pure silica sand, but that's unlikely. the regolith of ganymede will have all kinds of stuff flat out poisonous to terrestrial flora. soil is a very special thing, and damn hard to make. a cubic cm of soil can have 10,000 species of bacteria NONE OF WHICH CAN BE CULTURED.

people assume that plants are made of soil - not true at all. they are made of air. the only part that comes from the ground are micronutrients and nitrogen from bacteria. plants grow fine in sterile artificial growth media and/or water with added nutrients. in many cases, these are preferred as its easier to keep disease under control.

plants don't need or often even benefit from full spectrum light.



and in any case, the science of growing plants under lights and making lights for plants was licked long ago, before the new leds, even. if you like, you can have an aquarium with living corals, now, easily.

[Chen]

I think Ganymede also likely has a good amount of underground water. For the outer system, I have to imagine getting water in place to use for the plants is probably the biggest deal in terms of mass expenditure. Purely in terms of distance I think Ganymede is closer to the belt than Earth is (at their closest points). Whether the delta V required to get from Ganymede to various asteroids or not is less than that from Earth is unclear though (and fairly complicated to calculate).

[erikun]

if you like, you can have an aquarium with living corals, now, easily.

...but corals are animals.

Also, I concede that you display more knowledge of plant growth than I have. However, my understanding is that plants are both healthier and grow more nutritious food when grown in (at least) more "natural" situations when compared to industralized farming, and I would suspect that completely sterile farming from water, nutrients, air and light would likely be an even more extreme example. That is, while it would certainly still produce food, this would not be food as health as something grown in soil with an active polyculture surrounding it.

[tantric]

...but corals are animals.

Also, I concede that you display more knowledge of plant growth than I have. However, my understanding is that plants are both healthier and grow more nutritious food when grown in (at least) more "natural" situations when compared to industralized farming, and I would suspect that completely sterile farming from water, nutrients, air and light would likely be an even more extreme example. That is, while it would certainly still produce food, this would not be food as health as something grown in soil with an active polyculture surrounding it.

most of the shallow water reef-building corals, along with anemones, soft corals, giant clams, some sponges and other organisms harbor symbiotic algae called zooxanthellae within their bodies. for most of these corals, this is an obligate relationship - if something kills the algae, the coral will eventually die. i mentioned them because keeping them in an aquarium requires much more intense and special spectrum lighting than plants. most plants will grow under standard 'soft-white- flourescent bulbs. corals require 'actinic' bulbs that emit serious amounts of blue and UV.



i used to be an ecologist. while it's true that industrialized farming doesn't produce super healthy and nutritious plants, this is mostly because the plant varieties used have been bred for self-life instead of those things. it is also true that many plants benefit from mutualistic fungi that won't grow in hydroponics or artificial media. i said i used to be an ecologist, lately i've been a farmer. i practice sustainable agriculture (NOT organic) where i try to work with the local ecosystem instead of waging war against it, like traditional and industrial agriculture do.

but that was not at all what was being done on ganymede. it's possible to modify a terrestrial ecosystem to include agriculture but no way you're packing all that up and moving it to jupiter. it wouldn't work anyway - every species would have to genehacked for the rads and low g.

besides, read about cellular agriculture. if science can grow beef in a petri dish, i doubt it would be any more difficult to grow an apple.

[GloatingSwine]

kudos to 'the expanse' for putting the science back in science fiction, but a few things bug me...

ceres has a surface g of .03. it's been spun up to have spin g of .3. now, setting aside how much energy that would take, when the spin g exceeds natural g by an order of magnitude, wouldn''t it just fly apart?

That depends on the tensile strength, not the natural gravity.

In the series all that's left of Ceres is the core, the mantle, which is mostly ice, was stripped away and shipped to Mars for use in the terraforming initiative. In real life that probably wouldn't have enough tensile strength to hold together if it was used as an ersatz Bernal Sphere, but that's one of the allowable handwaves (like the reactionless Epstein drives).

[Palanan]

Originally Posted by factotum
In fact, [Jupiter’s] magnetosphere deflects solar radiation, and since Ganymede is well inside that magnetosphere it will be suffering rather *less* radiation than a random rock in deep space would.

Baseline solar radiation isn’t the main issue, since it’s relatively weak at Jupiter’s distance. The problem is that Jupiter’s magnetic field actually concentrates and intensifies charged particles in its radiation belts, which are similar to the Van Allen belts around Earth, but far stronger. This is an issue because the Galilean satellites orbit directly within Jupiter’s radiation belts. The safest place to live on Ganymede wouldn’t be right on the surface in domes, but under several meters of regolith.

Originally Posted by erikun
...but corals are animals.

Originally Posted by tantric
*zooxanthellae*

Tantric nailed it with the zooxanthellae. These are what can be tricky to keep alive—and when corals are stressed or unhealthy, they can actively eject the zooxanthellae, leaving the corals deathly white. This is called coral bleaching and is a major issue with many reef ecosystems today.

[tantric]

That depends on the tensile strength, not the natural gravity.

In the series all that's left of Ceres is the core, the mantle, which is mostly ice, was stripped away and shipped to Mars for use in the terraforming initiative. In real life that probably wouldn't have enough tensile strength to hold together if it was used as an ersatz Bernal Sphere, but that's one of the allowable handwaves (like the reactionless Epstein drives).

Epstein drives aren't reactionless - just highly efficient fusion. there's even an official online story about its invention. drivePDF

i forgive the ceres spinup for the scene where miller pours a drink and the liquid comes down at an angle due to Coriolis effect.

[Knaight]

plants don't need or often even benefit from full spectrum light.



and in any case, the science of growing plants under lights and making lights for plants was licked long ago, before the new leds, even. if you like, you can have an aquarium with living corals, now, easily.

These are the key spectrums for photosynthesis (it's not a great image, but the better textbook images have a tendency not to be put online); you'll notice that the entire visible spectrum sees at least some use. That's not to say that artificial lights are in any way a problem for growing plants, or that the full spectrum is actually necessary, but the one you posted isn't the complete story.

As far as the soil goes, that bit just seems weird. We have the technology for fairly decent hydroponics today, and while we tend not to use them because Earth has fairly good soil anyways and fertilizer production has been fairly easy ever since the Haber process got around nitrogen being a limiting resource, this doesn't really apply in space. Eventually dead vegetation grown in hydroponics could be used as a soil layer, but even if that had been built up the constraints on space still favor hydroponics. Then there's the matter of nutrient efficiency being a bit trickier when you don't have an atmosphere full of elemental nitrogen to synthesize ammonia with.

[tantric]

As far as the soil goes, that bit just seems weird. We have the technology for fairly decent hydroponics today, and while we tend not to use them because Earth has fairly good soil anyways and fertilizer production has been fairly easy ever since the Haber process got around nitrogen being a limiting resource, this doesn't really apply in space. Eventually dead vegetation grown in hydroponics could be used as a soil layer, but even if that had been built up the constraints on space still favor hydroponics. Then there's the matter of nutrient efficiency being a bit trickier when you don't have an atmosphere full of elemental nitrogen to synthesize ammonia with.

true, i over simplified and stand filled in ;-)

try growing an orchid hydroponically.

Orchid mycorrhizae are symbiotic relationships between the roots of plants of the family Orchidaceae and a variety of fungi. All orchids are myco-heterotrophic at some point in their life cycle. Orchid mycorrhizae are critically important during orchid germination, as an orchid seed has virtually no energy reserve and obtains its carbon from the fungal symbiont.[1] Many adult orchids retain their fungal symbionts, although the benefits to the adult photosynthetic orchid and the fungus remain largely unexplored.

Mycorrhizal fungi form a mutualistic relationship with the roots of most plant species. In such a relationship, both the plants themselves and those parts of the roots that host the fungi, are said to be mycorrhizal. Relatively few of the mycorrhizal relationships between plant species and fungi have been examined to date, but 95% of the plant families investigated are predominantly mycorrhizal either in the sense that most of their species associate beneficially with mycorrhizae, or are absolutely dependent on mycorrhizae. The Orchidaceae are notorious as a family in which the absence of the correct mycorrhizae is fatal even to germinating seeds.[4]

Recent research into ectomycorrhizal plants in boreal forests has indicated that mycorrhizal fungi and plants have a relationship that may be more complex than simply mutualistic. This relationship was noted when mycorrhizal fungi were unexpectedly found to be hoarding nitrogen from plant roots in times of nitrogen scarcity. Researchers argue that some mycorrhizae distribute nutrients based upon the environment with surrounding plants and other mycorrhizae. They go on to explain how this updated model could explain why mycorrhizae do not alleviate plant nitrogen limitation, and why plants can switch abruptly from a mixed strategy with both mycorrhizal and nonmycorrhizal roots to a purely mycorrhizal strategy as soil nitrogen availability declines

but you're right in that very few species of plants depend on these fungi. and assume either self-pollinating mutants or some genehacked pollinator.

i was trying to say that there's no need for actually plants. tissue cultures would do fine, and you'd really only need those for flavors. the bulk would come from bioreactors full of tailored yeast and algae. insane? in my mycology class we did a blind taste test: mcnuggets, microwaved chicken nuggets and Quorn chick'n nuggets made from fungal mycilia. quorn won every time.

[Knaight]

try growing an orchid hydroponically.

Hydroponics are generally intended for actual useful plants produced on an industrial scale. Something decorative can go in a flower pot just fine.

Plus, as you pointed out earlier it's not like the soil on Ganymede is any better.

[tantric]

Hydroponics are generally intended for actual useful plants produced on an industrial scale. Something decorative can go in a flower pot just fine.

Plus, as you pointed out earlier it's not like the soil on Ganymede is any better.

vanilla hater, you!