A Real 'Core World'

[Mithras]

I read somewhere about hypothetical 'cthonic' worlds which are the remaining metallic cores of gas giants that have had their hydrogen/helium atmospheres stripped off by an expanding star.

This is mine (slated for Aldebranan a K5III orange giant?):

ALDEBARAN C810459-A Poor, Non-Industrial

Now I pre-set the size and atmosphere, rolling everything else. I figured the world is extremely, dense, you're right down the the nickel-iron core
with perhaps a trace atmosphere of hydrogen/helium/ammonia. It was once a 'hot Jupiter' only smaller, and as the star expanded and the atmosphere boiled off, the planet's moons went awry. I can envisage several major strikes, and the world is canted at 90 degrees, like Uranus, and now close in to the star, is tidally locked with one pole facing the orange star.

A thick rocky belt orbits the world, remains of its inner moons destroyed during the calamity.

A 2G gravity?

Tidally locked. On the bright side, someone living at the pole will see the star never moving. Further south the star seems to move in a circle above their heads. At the day/night terminator, the cooler twilight region, the star seems to move along the horizon but never ever set. I think. Comments from astrophysicists and exo-geologists??!

Not touched on the population yet. 90,000 folk, in vacuum sealed domes or in abandoned nickel miner's tunnels. Feudal technocracy, hiring in experts to run the society, lowest bidder gets to run the domes or tunnel infrastructure, etc.

A competing faction are the agents of another world nearby...

Any comments ways to expand this, make the world special will be appreciated!

 

[Mithras]

Additional Note: I'm fleshing out my setting, creating my worlds for a cut-off star cluster. I want each world to have a real hook, either astronomical or geological. I don't want garden world after garden world differentiated by 'interesting cultures'. I can handle geology OK since studied it at high school and did a year of it at university, but my orbital mechanics and astronomy is shaky (but enthusiastic!).

 

[EDG]

ALDEBARAN C810459-A Poor, Non-Industrial

Now I pre-set the size and atmosphere, rolling everything else. I figured the world is extremely, dense, you're right down the the nickel-iron core
with perhaps a trace atmosphere of hydrogen/helium/ammonia. It was once a 'hot Jupiter' only smaller, and as the star expanded and the atmosphere boiled off, the planet's moons went awry. I can envisage several major strikes, and the world is canted at 90 degrees, like Uranus, and now close in to the star, is tidally locked with one pole facing the orange star.

It'd have to be damn close to strip the atmosphere away (plus the star expanded from its original main sequence radius, the current radius is about 30.6 million km, or about 0.2 AU. So if the hot jupiter was close to the original star, it'd be consumed by now).

Also, a jovian core isn't necessarily metal. If it does have a solid core then it's probably a large rocky planet with about 8-10 earth masses of rock with a metallic core, probably about 15,000 km in radius? It'd have some really weird geology as the planet decompresses after having millions of atmospheres of er... atmosphere (and liquid and solid hydrogen etc) removed from it.

The moons won't necessarily go awry, though the hill sphere radius would probably change so it may lose some to interplanetary space. As the planet loses mass, the orbits would expand and their eccentricities may change so some might crash into the core, but most would probably miss it and continue in unstable orbits.

 

[Mithras]

Thought as much ...

Idea ditched!

 

[Mithras]

Any other ideas for interesting worlds?

 

[GypsyComet]

Thought as much ...

Idea ditched!

Nah, just move it out as far as you can get it around an old, cold Dwarf star. Star went FOOM aeons ago and is now just an ember. This old metallic core is all that's left in the system, and has managed to sweep up a few wisps of gas since being stripped.

Maybe the world looks like someone took a hammer to one face, or maybe it looks like a forge accident.

The key is to use this trick only the once.

 

[Mithras]

Ah, the white dwarf - sounds plausible enough to me, there are several white dwarves within the cluster.

On the expanding K or M sun, is the problem that new exo-planets have been discovered that are within 2 or 3 AUs of a star and still retain their atmosphere? Meaning that a gasgiant stripped of its atmosphere would be in even tighter and closer???

If so - white dwarf it is.

 

[Supergamera]

Ah, the white dwarf - sounds plausible enough to me, there are several white dwarves within the cluster.

On the expanding K or M sun, is the problem that new exo-planets have been discovered that are within 2 or 3 AUs of a star and still retain their atmosphere? Meaning that a gasgiant stripped of its atmosphere would be in even tighter and closer???

If so - white dwarf it is.

If you like it, then do it! While it is nice to base closely off of current science, in the end, most players won't hold you to rigorous astrophysics, as long as they enjoy the setting.

 

[EDG]

Nah, just move it out as far as you can get it around an old, cold Dwarf star. Star went FOOM aeons ago and is now just an ember. This old metallic core is all that's left in the system, and has managed to sweep up a few wisps of gas since being stripped.

Maybe the world looks like someone took a hammer to one face, or maybe it looks like a forge accident.

The key is to use this trick only the once.

Puffing out as a planetary nebula won't cut it. You need a neutron star here - the star has to have gone supernova to blast off a jovian's atmosphere (and the jovian has to be pretty far out too). Though actually that might be overkill.

Maybe a type 1a supernova might cut it? That's when a WD in a close binary pulls off too much matter from the other star and explodes when it goes above 1.44 solar masses. I think those are lower energy than proper "supergiant goes foom" type II supernovae, so the jovian might actually survive.

 

[GypsyComet]

Could be. I would be more concerned with the appearance of the remnants than precisely how they got that way unless I also had a planetary scientist in my FTF group. Since the PhD in Geochemistry I used to play with could roll with a good fiction as well as anyone, I find I don't worry about it past "vaguely possible".

I would expect the system I described to have some sort of faint nebula in the neighborhood, but it could easily have dispersed to the point where this is almost a stealth system: A dim little solitary star, and only one significant mass.

 

[EDG]

Personally I'd say it's up to the GM how realistic he wants to make it, and it sounds like Mithras wants lots of realistic 'hooks' to make things unique (to which I say, "yay!").

Worldbuilding is kinda like art in a way - the artist defines the piece, not the viewer. And if the viewers may not appreciate (or even see) all the subtleties and nuances, but the fact that they are there is what makes it realistic.

 

[BP]

...Worldbuilding is kinda like art in a way - the artist defines the piece, not the viewer. And if the viewers may not appreciate (or even see) all the subtleties and nuances, but the fact that they are there is what makes it realistic.

Nicely put... and when someone decides to take a real up close look, its nice to see more than broad solid strokes covering the bland texture of the canvas!

Sci-Fi is seperated from Fantasy be its foundation in observed 'laws' and plausible theories.

 

[Mithras]

Yes, I want my physics to be spot on. My players won't notice, this is a grand world-building exercise and the creation is more important to me than the game (which is a bonus at the end of it all).

But in my mind, it has to all be plausible in some way.

Thanks for the additional comments EDG, that gives me something to work on.

 

[The Chef]

all this stuff makes my head hurt!