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Voyager Alpha - Worldbuilding IMTU

T

thalassogen

SOC-12
More than a week ago I posted this in my T5 Web Apps thread:

thalassogen said:
In the last week I worked primarily on another project...

For my own Traveller campaign I desired a more organic and more detailed star generation process and so I began to devise one of my own. The result is based on current astrophysics as far as I could get access to.

Stellar mass is generated using the Canonical Initial Mass Function. Stellar remnant mass is based on an observed initial-mass-final-mass relation for masses above 0.5 solar masses. Generated stars are aged through the main sequence and approximated/simplified evolutionary tracks based on initial mass. Radius, luminosity, and surface temperature (and thereby spectral and luminosity class) are calculated based on these internal models "for every day of a star's life". After a star's death its remnant's basic properties are also determined.

Stellar mass allows for orbital period calculations (aka year length). Radius provides needed details for Jump Drive operation. Change of luminosity is of interest to me because of changes in systems due to a heating up sun.

Would this alternate system (and that level of detail) be of interest to you?
Click to expand...

To discuss this system, its "scientific" foundation, its game-related usage, and upcoming implementations, I decided to start this thread to separate it from my T5 Web Apps that should firmly be based on Traveller 5 rules as written and not on personal preferences. Some of the results of this project may flow back into T5 one day (especially stellar radius and mass for obvious reasons).
 
I am currently looking for a way to calculate the snow/frost and rock lines of a system. Blackbody calculations based on early star's luminosity do not account for the temperature of the accreting disk itself and give really stupid results. Any hint towards a good treatment of the topic? My search fu is failing me and the next step would be a visit to the astrophysics library of the local university...
 
OK, this one got solved. I had my blackbody calculations wrong - that accounts for the stupid results - and I had to investigate pre-main sequence protostars (T Tauri and family). Their luminosity is much higher than the newly created main sequence star. I account for this by increasing the luminosity accordingly and am getting nice results now.
 
thalassogen said:
My next broad steps are:
- creation of planetary systems
- creation of worlds
- creation of life
Click to expand...

This is really interesting, thanks for this.

There is a program called Accrete, based upon Rand Study which generates worlds from the protoplanetary disk to the final rocky (or gas giant) bodies. It may be a really interesting point to start for the next phase.
 
thalassogen said:
OK, this one got solved. I had my blackbody calculations wrong - that accounts for the stupid results - and I had to investigate pre-main sequence protostars (T Tauri and family). Their luminosity is much higher than the newly created main sequence star. I account for this by increasing the luminosity accordingly and am getting nice results now.
Click to expand...

Here's what I have:

Ice line: the orbital radius at which water molecules will condense into
ice. Inside this radius H2O ice will sublimate into vapor @ 152 K.
AU = sqrt(L)×2.7, solar constant ~ 188 W/m², albedo = 0.36. Terrestrial
planets and planetoids form inside the ice line, gas giants form outside it
(later they may migrate inward). During system formation, the ice line moves
outward as the protostar ignites and heats up.

Dust sublimation boundary / photoevaporation radius: the distance where
rocks (pyroxenes & olivines) and dust grains volatilize @ 800 - 1500 K,
sort of a "ice line" for silicates. AU = sqrt(L)×0.051, solar constant
~ 531 kW/m², albedo = 0.115. Planets cannot accrete inside this zone, but
large ones may migrate into it after accretion and survive intact. AKA 'Rock line',
the untenable orbits in the 2300 ref's manual
 
I don't know if it's of any use, but Tyge Sjöstrand was working on a set of system generation rules back in 2000. He eventually abandoned it but there are links to an HTML version and a PDF version here.
 
It is of use, thanks! Although stellar data is as wrong as most older rpg stuff (giant stars are not a separate class of stars but a life time stage and thereby cannot be more massive than the original main sequence star they developed from), but atmosphere and climate chapters look very interesting to me. Thanks again!
 
At last, multiple star systems are done! http://heldenhaufen.de/Va/Worldbuilding/RandomStarSystem

Sometimes the orbital configuration isn't very stable and this will have to be fixed during the next update, but for now I am satisfied with the result. And maybe I will even keep unstable orbits for very young systems.

Decoding the Orbital Configuration:

( ( D [HSR:9.23AU] <58.95a-13.45AU> [HSR:2.36AU] L2VI ) [HSR:25.88AU] <294.77a-41.47AU> [HSR:7.99AU] M8VI )

- Parentheses ( ... ) surround pairs
- The parts of the pair are listed at the beginning and at the end ( D ... L2VI )
- Values in angle brackets < ... > denote the orbital period and distance of the pair
- Values in normal brackets [ ... ] represent the hill sphere radius for stable prograde orbits around the specific part of the pair

D and L2VI are 13.45 AU distant and orbit their common center of mass in about 59 years. D can have its own planetary system out to 9.23 AU and L2VI out to 2.36 AU. Their common center of mass is orbited by M8VI at a distance of 41.47 AU and in about 295 years. D-L2VI is stable due to their hill sphere radius in relation to M8VI: 25.88 AU is much larger than the separation of D and L2VI. Their planetary systems are also safe from M8VI. And M8VI itself may have a veritable planetary system, maybe even the more interesting one due to the planetary nebula that may have destroyed most habitable worlds in the D-L2VI subsystem.

TODO: Find a more readable notation for multiple star system configurations.
 
All inner limits and sub-group outer limits defined - but how about an upper limit? Any good hints toward a planetary systems outer limit?
 
thalassogen said:
All inner limits and sub-group outer limits defined - but how about an upper limit? Any good hints toward a planetary systems outer limit?
Click to expand...

A star system's outer extent probably won't exceed the the size of the original protoplanetary disc.

Stars can form quite close together in a stellar nursery; I think this is the reason for so many binaries. A nascent star's outer planets can be stripped away by nearby protostars.

Without putting much thought into this, I'd say calculate the Hill radius of the parent protostar(s) in the presence of its siblings. Stable orbits around them should exist with about 40% of that radius. This should define the limit of the cometary halo. Planets will be found much closer in.
 
That's a good idea! As parameters, I used the mass of the Milky Way (180e9 sol), the sun's distance from the center (27e3 ly), and arrived at 3.3 ly, 40% = 1.33 ly. That's what's given in literature. Using Alpha Centauri as the nearest reference point, I get 2.4 ly, 40% = 0.96 ly. Also, the typical limit of the Oort Cloud. That's good enough for the typical system extent for me.

I am looking for the outer limit of "real" planets as rough guideline, too. For that literature sometimes gives 40 AU for our solar system. Therefore I will use: Outer Limit = 40 AU * Mass^0.5 as that guideline I think.
 
Basic Orbital Parameters done, stellar and planetary! Advanced Parameters (eccentricity and inclination) still to come. Planet generation will be next.

The system description string gets more unreadable and includes many control parameters not needed in the final listing. I added {inner=/outer=} limits for each component, extended [HSR:/RL:] by roche lobe radius, and appended planetary orbits [nnnAU, nnnAU, nnnAU] that stay within {inner=/outer=}.
 
thalassogen said:
The system description string gets more unreadable and includes many control parameters not needed in the final listing.
Click to expand...

At this point you may want to think more about separating the data string from the display. For example, the UWP (a very short code) is readable by people who have managed to memorize the columns and values. But is unreadable by most people. In the wiki we solved this problem by having the UWP on the page, but a mouse-over popup which expanded the to a larger set of text for the UWP-illiterate to use and understand.

So concentrate on making the system description string consistent to allow a computer parser to read and expand it for better display. Don't assume a person (or only a person) will be reading it.

The most painful aspect of building a .SEC (sector file) parser was there were so many standard formats...
 
I started generating UWPs and updated the website. Currently only Size is calculated. Next will be Atmosphere, Hydrosphere and Biosphere.
 
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