What are some of the ramifications and consequences of this world's'"exoticness"?

Question

For my Science-Fantasy WIP I am considering using a single artificial planet (roughly the size of a Dyson Sphere) and its moons (of which only three are large enough to exert any real influence) as my setting. While I loved the star-hopping feel of space opera, the logistics just proved to be a headache. So I'm going for something vast far beyond earth in scope, but still less than the infinity of the cosmos.

In addition to its size the world has "exotic" and perhaps supernatural geological process. All the land masses grow from and occasinaly collaps back into an alchemical sea. Deep inside the world there is a great perpetual power source, an energy to matter converter which produce the alchemicals and conduits that feed them to the surface. And an assembly process that forms the land masscess from the building blocks supplied by the core.

The world with a toxic sea was "inspired" by the planet Haruun Kal.

My Questions:

1. What effect would the planet's size have on the weather and climate?
2. How might having multiple moons effect the tides?
3. What, if any, natural process could explain how the chemicals of the toxic sea separate from water? So that all rain isn't poisons and caustic,occasional acid rain is fine a natural hazard.

4.on a Dyson Sphere sized world what is the distance in miles from the equator to the Arctic circle.

5.Which is the "better" of two explanations for the formation land masses. Nano-assemblers building them out the material in the alchemical Sea. Or the land masses are not land as we know it at all. But massive leafless plants with rock like bark.

Answer 1

Make it hollow.

On the scale you're talking about, hollow is a relative term. Think of a shell several thousand miles through, which gives you localized gravity and enough room to have your eldritch/alchemical engines, geological processes and toxic seas. That way you can have a human-friendly gravity on a "planet" of any relative size. I'm not up to calculating exactly how thick it would need to be, but I suspect the answer will be roughly on the order of 1/2 to 1/1 Earth's diameter. Your central power source (star?) can still be in the center, and can power everything purely through radiation.

There are several unresolved issues you will need to consider:

1. You need some sort of super-strong lattice to support and keep your structure in its 1 AU-radius sphere form. Otherwise at some point it will collapse into the center and implode.

2. The mass of this thing is insane. If it's 10,000 miles thick and is 1 AU in radius, then it's roughly 10^21 cubic miles of material. If it's mostly rocky, it weighs around 2.6 x 10^37 kgs, or roughly 1 million solar masses. So you'll need something to go around eating stars to build this, which might take a while.

3. I'm not sure how you can light it. The problem is that a single star won't provide enough light across the entire thing - you're only going to get parts of the equater in the habital zone, and the rest of it will be covered in ice. You might be ok if you had multiple "suns" in polar orbits around your planet, so they hit all latitudes as they go by while still providing a day/night cycle. They can't actually be suns, because stars are too massive and would pull your planet apart. So instead you need artificial light sources. You can simulate seasons/climates by varying their inclination on a yearly basis (tilting the planet back and forth basically).

Answer 2

The biggest problem I see is that your planet would be uninhabitable for humans. The gravity alone will be a huge obstacle. Jupiter is 2.4 times stronger than that on earth. So the people living there would have to be modified, much larger and stronger skeletal system, much larger muscle mass etc.

The next problem is the larger the planet the more hydrogen it will have trapped in it's atmosphere. This isn't really any good for anyone, since (at least humans) need oxygen and these to elements are very reactive.

Jupiters atmosphere is ~%90 hydrogen and ~%10 helium. not very useful for any life as we know it.

You would be much better off putting all of your sentient beings on the moons surrounding the planet, they could of course mine the atmosphere for hydrogen for fuels etc.

Oh ya, you also have to deal with the body crushing air pressure.

Answer 3

Well I'm sure I won't be able to provide valuable answers to all of your points, (or maybe not even answers @ all to some of them) but here are a few thoughts:

First
I would suggest doing as much as you can to fit into normal science before moving to handwavium.

Here are what I would consider your biggest roughly science based problems with this planet (to which I will suggest some solutions to after):

1. Gravity... the gravity of a large body will, by reason of it's increased mass, be greater the greater the mass.This can pose many problems including limiting the size of the indigenous life, limiting the ability to leave the planet, and a few others I will mention below.
2. The likelihood of development of powerful radiation belts (so long as there is a chance they could affect the surface or the peaks that the inhabitants live on)
   Based on this article the affect might only make the poles uninhabitable.
3. The affect of gravity on the composition and thickness of the atmosphere.
   A higher gravity will attract & keep more gases, which will increase pressure as well as types of gases... which may make it harder for a simple enough atmosphere to provide enough of one particular type of chemically reactive gas (like oxygen), to allow living beings to breath it (handwavum may be required).
4. Increased size, gravity, & proximity to the star could make it more of a target for collisions with comets, asteroids etc...

Some Possible Solutions

An approach that might solve a number of the problems is to have this planet located in a solar system that has a main sequence star which has transitioned to burning helium, and become a red giant. This possible solution could work so long as:
- the planet is not too close to the star,
- the star doesn't expand too much,
- and that there was enough of a rocky core initially in the planet before it became a gas giant

So Given the above requirements here are the ways this proposed solution could be utilized, (with some handwavium, but not too much, applied):

1. The risk of celestial bombardment would decrease because the incidence of large non-planetary bodies should decrease with the age of the solar system, the increased circumference of the star would eat most that formerly came into the inner solar system, and a gas giant has the potential for a number of moons and/or larger moons, that may help protect it.
2. Through the explanation provided here you could (with a little not-quite-scientific explanation) provide for the toxic oceans as being the remaining heavier atmospheric gases or atmospheric condensates (such as acids).
   This would allow you to also have the reasonably normal atmosphere, (water rain, oxygen-nitrogen atmosphere, etc...), while still having the oceans. It could also explain some smaller bodies of actual water above the level of the toxic oceans.
3. Using this solution of starting with a gas giant that is then stripped of much of it's excess atmosphere, you could also explain it's large size as, generally speaking, larger planets become gas giants.
4. This would also likely give you a smaller planetary mass than jupiter to avoid the problems of excessive radiation and gravity on your planet. I would suggest shooting for maybe 20 times the surface of earth instead of the 'surface' area of Jupiter 120.
   While I suspect it's likely you are attempting to take into account the fact that denizens of this planet only live on mountains and highlands of the rocky core, due to the large ocean, while still leaving enough habitable area for them to live. These mountains and highlands really amount to islands. If you remove the largest continents, increase the size of the remaining islands and multiply that surface area by 20 I suspect there would still be plenty of habitable area.

Interesting idea, and I hope this helps.

Answer 4

To question 4 - a dyson sphere would encompass a star, so you are talking something with a diameter equivalent to the orbit of a planet. Take Mars, with a distance to the sun of just under 150 million miles. If you make a Dyson sphere around the sun, at Mars' orbit, the distance from its Equator to one of its poles would be around 230 million miles. The earth's arctic circle is at 66 degrees North. So this Dyson sphere's arctic circle, if it was defined to be at the same latitude, would be about 172 million miles from its equator.

I estimate that at the speed of sound it would take you around 25 years to go from the equator to the arctic, or just over 300 years to circumnavigate the sphere.