World Generation in 2300AD

[Tanuki]

Thanks, Thomas.

I've sent Dr. Ganymede scans of the worldbuilding pages of 2300AD -- just so we're all on the same page here.

I've asked to look in particular at the tables on pages 89-92, where density runs from .1 to 1.4 earths and diameter runs from 1000 to 48,000 kilometers and every space on every table is filled in with a 4 digit pseudo-accurate number. These were probably generated by simplistic spreadsheets with no real check with reality.

Hence 48,000 kilometer worlds with a density of .1 earths, etc.

 

[snrdg082102]

You are welcome Tanuki,

As usual for a sailor, even a retired one, I am day a late, a dollar short, and have only provided a quarter of required documents.

Have a dry day.

Originally posted by Tanuki:
Thanks, Thomas.

I've sent Dr. Ganymede scans of the worldbuilding pages of 2300AD -- just so we're all on the same page here.

I've asked to look in particular at the tables on pages 89-92, where density runs from .1 to 1.4 earths and diameter runs from 1000 to 48,000 kilometers and every space on every table is filled in with a 4 digit pseudo-accurate number. These were probably generated by simplistic spreadsheets with no real check with reality.

Hence 48,000 kilometer worlds with a density of .1 earths, etc.

 

[Pompe]

First, for Colin. It is nice to hear you've started on the planet design rules. I don't know if or what kind of assistance you want, though.

That the density tables for 2300AD's world generation (as well as for a few of the actual worlds in 2300AD too - like Heidelsheimat and Daikoku) are dubious goes in with the general criticism of the charts in the Director's Guide. I think I've said it before in this forum.

(I might add that it isn't just density, but atmosphere pressure too. And likely the entire minimal-molecular-weight-retained stuff.)

But when it comes to extreme densities for planets there is one category which can be expected to routinely have much higher densities (as well as needing modified generation rules from about any published worldgen system out there): very large gas giants. Their mass can compress them to densities above the terrestrial planet norm.

 

[Colin]

One of my goals is to reduce chart creep, but at the same time ensure that the system can actually generate both the planets already in canon, along with some real ones. (At this point, I don't think it can create Mars.)

However, that being said, I don't want to stray too far from the T20 and/or 2300 system/world generations systems. Part of this is compatibility with the earlier works, and a good part of it is time, which I don't have enough of. Starships (esp.) and vehicles have consumed far too much of that time. There's real writing to be done.

I appreciate any suggestions people on this forum may have. I cannot guarantee that I will use them, but I will look at them and give them consideration. My own specialty is geography, in particular human geography, so a view from the science side is welcome.

Colin

 

[Tanuki]

Originally posted by Colin:
My own specialty is geography, in particular human geography, so a view from the science side is welcome.

Cool. My degree is in physical geography, with a minor in biology. It was about as close as I could get to "worldbuilding" in a university setting.

 

[EvilDrGanymede]

Originally posted by Tanuki:
</font><blockquote>quote:</font><hr />Originally posted by Colin:
My own specialty is geography, in particular human geography, so a view from the science side is welcome.

Cool. My degree is in physical geography, with a minor in biology. It was about as close as I could get to "worldbuilding" in a university setting. </font>[/QUOTE]Well, my PhD's in planet-building, so nyah!

(no, really, it is. I spent a good chunk of it making internal structure models of the moons of Jupiter

)

 

[Colin]

I've been doing some work on the world-building section, and have a few questions/comments.

For a planet to have a magnetic field, it must have a molten core (well, a solid core in a molten outer core, I'll leave the mechanics aside)

For a planet to maintain a molten core over time, it needs a massive moon (or be a moon of a gas giant). Tidal effects keep core molten after effects of radioactive heating start to fade.

Planets without a magentic field lose their atmosphere over time to abrasion by solar wind particles.

A massive moon may be required to prevent a Venus-type planet (heavy moon strips away denser atmosphere).

In the long run, habitable planets need a massive moon and a magnetic field.

So the base world could have an atmospheric pressure equal to the surface garvity (ala 2320 world design) but that atmosphere type is modified by other factors, like whether or not a world has a magnetic field, or a massive moon, and how old the world is.

I do want to avoid massive charts, but at the same time I want to avoid massive formulas. This is a game, not a simulator, though I do want it to generate useful results. As realistic as possible, but also fun.

Comments?

Colin

 

[Pompe]

Hmm.

Personally I think you are overstating the importance of a large moon present. I believe most of the internal heat of Earth is radioactive - a smaller part, something like 1/5, is left-over heat from formation. When radioactivity dies down, the moon won't be enough, you'd need an Io-like situation.

But it can be argued that the large moon aids (or allows) plate tectonics. Just how much, well.

And on any planet in a habitable zone, there still is a significant other source of tidal force - the star. The sun has about 40% of the moon - less, but still quite significant. On a world around a dimmer star, like several of those in 2300AD, the star might be more influential in rising tides than the moon and sun are combined on our world.

That a large moon would be needed to strip away atmosphere I've seen in print before, but I don't recall where. One question is however if you really need a moon, or if not just a serious enough impact bombardment (which need not leave a large moon) would be just as useful. I think one could say that a normal Earth-size world probably has more water and more atmosphere than Earth, but that does not mean there are others with less than our own. I could imagine quite some variation. Furthermore, I don't think base pressure should be just related to gravity but to planetary size (volume) as well.

Magnetic field is definitely useful. (More so than a moon, I think). Still, the world could have less magnetic field if say
1) it orbits a less active star, like a K-V.
2) the planet had a stronger magnetic field when it was younger, because the solar wind is likely by far most erosive in the early solar system
3) the planet starts out with a rather dense atmosphere which is layered efficiently
4) it simply hasn't had enough time to lose the atmosphere

When it comes to realism, I'd agree it is desirable, but at the same time, it likely should be compatible in result to the worlds of 2300AD. And several of the tougher issues in planetology are not exactly resolved, so it is in many ways a matter of opinion. (Like how important a moon would be. Stabilizing the axis has been one such thing - but then it might be that planets with non-stable tilt may be good, not bad...)

Still, there is more known about how planets work now than 10-15 years ago. And it would be exciting if such advancements would be incorporated.

 

[Anthony]

I don't really see how a moon would strip away all that much atmosphere; an extra 20 microgees seems unlikely to do that much to the rate at which atmosphere escapes. Critical issues that I remember:

Big enough that the atmosphere doesn't leak away
Small enough that you don't wind up with a subgiant or gas giant.
Water, to bind CO2 out of the atmosphere.
Plate tectonics, to recycle material collected by the oceans.
A planetary magnetic field reduces heat in the upper atmosphere, so allows a smaller world to maintain an atmosphere. However, a sufficiently large world can keep its atmosphere anyway. In any case, any world with plate tectonics is likely to have a magnetic field.
Temperature low enough that the partial pressure of water in the atmosphere remains low enough; if too much water gets into the atmosphere, photodisassociation in the upper atmosphere causes loss of the hydrogen.
Temperature high enough that the oceans remain liquid.

 

[Whipsnade]

Anthony wrote:

"I don't really see how a moon would strip away all that much atmosphere;..."


Mr. Jackson,

It won't. That idea is a cultural echo of a sorts. Please bear with me.

Back in the early to mid 60s, a large moon was thought to be necessary for the formation of a relatively thin atmosphere. Towards the end of that period, Larry Niven managed to insert the idea into nearly every short story he wrote and the idea gained wide currency. By the early 70s, we knew the 'Large Moon Idea' to be wrong, but Niven's hugely popular works had pumped the idea into the sci-fi mainstream and into the heads of many sci-fi readers and so the idea was 'stuck'. Niven and planetary scientists have been dealing with the echoes ever since.

Niven makes reference to this in some of his short story collections printed in the late 70s. He also mentions it in the two anthologies he published in the 90s.

This really isn't Niven's fault. After all, he didn't know his Ringworld would need attitude thrusters until those MIT students told him at a 'con. He got lucky enough to write that correction into his Ringworld follow-ons.


Sincerely,
Larsen

 

[Pompe]

Thank you, Mr. Whipsnade. I don't think that is where I read about it, but it might well have been in an older work. i searched through my more recent planetology-oriented literature (less than ten years old, that is) and found no such reference. In say, "Rare Earth" (2000), the main use for the moon is to stabilize the spin, induce massive short-lived surface heating due to tides and to blow away volatiles by the formation impact.

I'd still say that the presence of a large moon as remnant of Great Planetary Bombardment could be a good way to see that the world has lost a fair deal of volatiles. But there is no need for a remaining moon, nor is the presence of a large moon necessarily indicative of such - it could have been captured in the early system.

 

[Colin]

Hmm, I don't recall that I got that out of Niven, but it may have been hanging out in my brain for awhile. The last book on planetology I read was the aforementioned Rare Earth, but even that's been a couple of years. I plan on raiding the main stacks over in the Science library this weekend for some more info. (The benefits of being staff at a large university).

In any case, planetary science isn't my field, which is why I posted here before writing anything down. I don't plan on doing much to the 2300 world generation system, largely integating them with the current T20 rules, but I would like the system to actually be able to build real worlds. (IE, you can't make Mars with them as they stand).

Thanks for the responses.

Colin

 

[Whipsnade]

Gentlemen,

Larry Niven merely popularized the 'Big Moon Means No Venus-Type Atmosphere' in his early work. You may have first read about it or heard about it other media.

Colin - May I suggest you PM Dr. Constantine Thomas, aka Dr. Evil Ganymede, a regular here at CotI with your questions? He is an actual planetary scientist. He's done a great deal of work concerning Jupiter's moons, IIRC. Perhaps he could point you to a way around your 'Cannot Generate Mars' problem.


Sincerely,
Larsen

 

[salamander]

Originally posted by Evil Dr Ganymede:
(no, really, it is. I spent a good chunk of it making internal structure models of the moons of Jupiter

That has to be one of the coolest things I've heard from someone playing Our Great Game!

Can we pick your brains? Huh, can we?

 

[Murph]

How about something fast and dirty so players and GMs can get rolling fast?

 

[Murph]

Colin, any update on planet design?

 

[Colin]

There will be no planet design system in the initial book. It will have to wait for the "Explorer's Handbook", and that project is really only in its nascent stages. In the interim, the T20 system can be used, though care should be exercised to keep the worlds generated consistent with the 2320AD flavour.

 

[Peter Schutze]

the biggest difference from sci-fi games to recent discoveries is 'hot jupiters'

are we going to allow 'hot jupiters' etc into 2320 ? They are the most common planet discovered so far but thats because of a very biased discovery mechanism (easiest to find big planets close to stars)

They should simplify system generation enormously ! If you get one of them in orbit 1 or 2 they've probably wiped out the "rocky band" planets during their migration inward so thats about half the generating eliminated <smile>

 

[Anders]

the biggest difference from sci-fi games to recent discoveries is 'hot jupiters'

are we going to allow 'hot jupiters' etc into 2320 ?

I'm all for them. They make really cool (hot) environments. Just think about the scenery among their moons as atmosphere billows outwards, providing ample opportunity for starships to hide and possibly even Earth-like moons. OK, those moons would suffer exceedingly long days since they would likely be tidally locked and get a sun-cycle depending on their orbit around the giant, but they would definitely be interesting places. I developed one such world for another setting, and there are plenty of interesting effects.

They should simplify system generation enormously ! If you get one of them in orbit 1 or 2 they've probably wiped out the "rocky band" planets during their migration inward so thats about half the generating eliminated <smile>

Not so fast! Check out "On the possibility of terrestrial planet formation in hot-Jupiter systems" by Martyn J. Fogg and Richard P. Nelson, International Journal of Astrobiology (2006), 5: 199-209 Cambridge University Press. Their simulations show that enough solid material (60-80%) remains from which terrestrial planets can develop even after a migration. On the other hand, a lot of volatile material has been driven into the inner system, making waterworlds likely. Protoplanets tend to start out with big eccentricities but are likely to circularize; I would expect such systems to have more planets in high eccentricity orbits though.

 

[Anders]

If I were to make any recommendations about planet creation it would be:

Add eccentricity as a possibility - most larger planets will have circular orbits, but smaller and a few terrestrial may have appreciable eccentricity. Actually, garden worlds may function even with pretty eccentric orbits (see Darren M. Williams and David Pollard, Earth-like worlds on eccentric orbits: excursions beyond the habitable zone, International Journal of Astrobiology (2002), 1: 61-69 Cambridge University Press). This is probably handled best as a separate roll for each planet whether it suffers unusual eccentricity.

Axial tilt: this can make planets very different. We have a range in the solar system from 0 to 177 degrees. Planets with near 90 degree tilt have warmer equators than poles, and quite bizarre weather (Darren M. Williams has a simulation paper about terrestrial tilted planets too). I would guess tilt can just be calculated as (say) 1d6 x 1d6 x 1d6 degrees to get a nicely skewed distribution.

Rotation rate: important, since it powers the weather together with the sun. Fast rotation means many Hadley cells, and a more east-westerly (and stormy atmosphere), slow rotation creates bigger weather systems and more of a front-style weather. Unfortunately calculating plausible rotation rates appears hard and complex.
http://www.johnbray.org.uk/planetdesigner/science/science.html

I think the old system produced double planets often enough to be plausible - the first system I ever made got a nice double asteroid pair that at the time looked very cool and odd, but now seems to be quite similar to what we see all over the solar system.

Resist the temptation to make gardens easy and common! Pregardens, postgardens, glacier worlds and hothouses cover a lot of territory. Waterworlds should likely be encouraged, especially if it is a high gravity world - it seems likely that many planets have exceedingly deep oceans. Whether they could sustain life is an interesting question.

I like using just formulas (one reason I loved 2300AD was that it was the only game with a cube root formula in it), but many gamers do not. Tables take a lot of space. Maybe just distribute the formulas but make a simple on-line generation system?