Creating the Manticore-A system in StarGen

So, I've been playing around again with StarGen, a program by Jim Burrows (based on the ACCRETE program) that creates whole solar systems and habitable planets. There is a web-interface here so you can run it from your browser. It's really cool, and provides a lot of data for the planets made

Anyway, there is an option to output only systems with two habitable worlds for stars with sufficient mass, and I never before realized it, but it turns out many such systems are like Manticore-A's two habitable worlds, Manticore and Sphinx. One example is with stellar mass 1.1 (should be typical for a G0V star), seed 4, and repeat count of 7000. The system called stargen391-1.1 in the output thumbnails looks like it has Manticore and Sphinx. I'm not sure if David did any research or simply designed his planets to meet story requirements, but he hit it pretty dead-on.

One thing he DID overlook is that a high-g world like Sphinx located as it is in the Manticore-A system is going to retain helium--around 25% of the atmosphere. Not surer what effects this might have on people, but life on Sphinx might actually be rather...interesting. This also means that a realy high-g world like San Martin is complete fiction. That high a gravity would most likely hold onto a substantial hydrogen and helium atmosphere; not a gas giant, but a "gas dwarf". In fact, this is the highest-gravity world with a breathable atmosphere that the program created. I know David has a fondness for high-g worlds, but realistically, 1.3 g seems to be the upper limit.

I have no idea how this program calculates the atmosphere of the planets. One major point I would ask is, does this program only produce primordial atmospheres? I doubt that the program is designed to produce atmospheres after they have been modified by life or other chemical modifications that occur on planets. Recall that there was a considerable amount of hydrogen, and ammonia, and methane, in Earth's atmosphere originally, too. The presence of life makes an enormous difference. The atmosphere of Earth today is very different from what was originally formed, and that is undoubtedly true of Manticore and Sphinx as well. The atmosphere of Mars is also very different from when it was first formed.

What atmosphere does it give for the Manticore-analog? I'm curious what it comes up with.

It sounds like a fascinating program.

Oh, it's fascinating, alright. You have to use the command-line version to get them, but the program can create a habitable planet for a star down to .62 solar masses (have to do a repeat count of at least 2 million though). The full details of the program can be found at http://www.eldacur.com/~brons/NerdCorne ... arGen.html

I forgot to add that the "Use atmosphere model" option should be checked, as it provides a breakdown of the atmosphere by percentages and ipp.

For the "Manticore" analog, I went with a "Warm" earth (out of many results) since that seemed to be more like Manticore is in the books--little ice cover. This particular example has a surface pressure of 923 millibars, molecular weight retained of 7.7, which means the gases N, O, CH4, NH3, H2O, Ne, N2, CO... The major components are:

Nitrogen 72.6% 670 mb (ipp: 625)
Oxygen 26.5% 245 mb (ipp: 228)
Argon 0.8% 7 mb (ipp: 7)

61Cygni wrote:Oh, it's fascinating, alright. You have to use the command-line version to get them, but the program can create a habitable planet for a star down to .62 solar masses (have to do a repeat count of at least 2 million though). The full details of the program can be found at http://www.eldacur.com/~brons/NerdCorne ... arGen.html

I forgot to add that the "Use atmosphere model" option should be checked, as it provides a breakdown of the atmosphere by percentages and ipp.

For the "Manticore" analog, I went with a "Warm" earth (out of many results) since that seemed to be more like Manticore is in the books--little ice cover. This particular example has a surface pressure of 923 millibars, molecular weight retained of 7.7, which means the gases N, O, CH4, NH3, H2O, Ne, N2, CO... The major components are:

Nitrogen 72.6% 670 mb (ipp: 625)
Oxygen 26.5% 245 mb (ipp: 228)
Argon 0.8% 7 mb (ipp: 7)

That's very interesting. Apparently the program is assuming the presence of life or some other extreme aberration in the atmosphere. Free oxygen is not stable in that atmosphere; if is present, it means that some unusual chemistry is happening (such as life). Since we have no other examples of atmospheres with free oxygen, it has to be extrapolating from Earth's atmosphere.

If the Sphinx-analog does not have free oxygen, then the program is not making the same assumption. Do you think there is any way to convince the program to produce an oxygen atmosphere there? I'm not sure how it could extrapolate an oxygen atmosphere to a planet like that when we have no examples to model it on.

Fascinating Have you run this for any other of David's worlds? Like Safehold?

SWM wrote:That's very interesting. Apparently the program is assuming the presence of life or some other extreme aberration in the atmosphere. Free oxygen is not stable in that atmosphere; if is present, it means that some unusual chemistry is happening (such as life). Since we have no other examples of atmospheres with free oxygen, it has to be extrapolating from Earth's atmosphere.

If the Sphinx-analog does not have free oxygen, then the program is not making the same assumption. Do you think there is any way to convince the program to produce an oxygen atmosphere there? I'm not sure how it could extrapolate an oxygen atmosphere to a planet like that when we have no examples to model it on.

No, the Sphinx analog has oxygen too, I do think the program is taking into account the presence of a biological oxygen-producing source when it comes up with a habitable planet.

Here are some partial "Sphinx" stats:

Terrestrial: High-G, Cold, Wet, Few clouds, Thick atmosphere (N2, He, O2 - breathable).

(That means its physical stats are a bit greater/lower than Earth's, i.e. higher gravity, cooler average surface temp, more surface area covered by oceans, etc.)

Distance from primary star 2.5E+08 KM 1.652 AU

Mass 1.2E+25Kg 2.082 Earth masses

Surface gravity 1270.0 cm/sec2 1.30 Earth gees

Surface pressure 3991 millibars 3.939 Earth atmospheres

Surface temperature 7.8° Celcius 46.1° Fahrenheit

-6.2° C Earth temperature
-11.1° F Earth temperature
+6.8° C greenhouse effect

Normal temperature range

Night Day

5.8° C - 9.7° C
42.4° F - 49.5° F

Min Max

-6.9° C - 21.8° C
19.7° F - 71.2° F

Molecular weight retained 2.3 and above
He, N, O, CH4, NH3, H2O, Ne, N2...

Nitrogen 72.0% 2875 mb (ipp: 2830)
Helium 24.9% 996 mb (ipp: 980)
Oxygen 2.6% 102 mb (ipp: 100)
Argon 0.5% 18 mb (ipp: 18)

Axial tilt 35°

Planetary albedo 0.22

Hydrosphere percentage 83.6

Cloud cover percentage 37.7

Ice cover percentage 4.7

The program is not perfect, and hasn't been updated in years (the Windows version doesn't seem to like Win7, so I use the CMD to run the command-line version), and doesn't do moons except for a very experimental and limited option, but it's the world-building program I've been looking for, since it comes up with plausible habitable worlds (including Earth clones) for universe-building and provides much hard data on them.

fallsfromtrees wrote:Fascinating Have you run this for any other of David's worlds? Like Safehold?

I haven't read the Safehold books yet, so can't say anything about that, but I did come across a Grayson analog in one of the Stargen runs--an Earth-like and sized world with a higher-than-Earth density. Must have lots of heavy metals.

61Cygni wrote:One thing he DID overlook is that a high-g world like Sphinx located as it is in the Manticore-A system is going to retain helium--around 25% of the atmosphere. Not surer what effects this might have on people, but life on Sphinx might actually be rather...interesting.

As far as I know, 25% helium is pretty much completely harmless on a period of weeks at least. Saturation divers breath it for that long on a single job. Unless under a lot of pressure, like 400 feet of seawater, there really are no physiological issues. However helium is a wonderful conductor of heat, and you get cold faster in a helium atmosphere.

Rooting around on the Stargen website, I found the following:

Keris also has a simple model for calculating which elements are liquids and gases for the temperature and pressure of each planet. It then calculates reasonable abundances of each material. I simplified his model to cover only the major atmospheric gases. The resulting model has very little basis in reality or current science, but produces interesting results.

This explains why so many of the interesting planets have oxygen - its part of the model. Therefore, the results should be used a little sparingly, unless we can get RFC to cough up the values (and program) he used to generate Safehold, so that we can get a feel for atmospheric pressure, etc.

fallsfromtrees wrote:Rooting around on the Stargen website, I found the following:

Keris also has a simple model for calculating which elements are liquids and gases for the temperature and pressure of each planet. It then calculates reasonable abundances of each material. I simplified his model to cover only the major atmospheric gases. The resulting model has very little basis in reality or current science, but produces interesting results.

This explains why so many of the interesting planets have oxygen - its part of the model. Therefore, the results should be used a little sparingly, unless we can get RFC to cough up the values (and program) he used to generate Safehold, so that we can get a feel for atmospheric pressure, etc.

Yeah, that explains all the "Ice" planets with breathable atmospheres, something I found puzzling. However, most of those aren't solid frigid iceballs, but just have no liquid water on the surface, only a portion of which is ice-covered. The temps range to above (sometimes well above) freezing as well, at least at certain times and locations. So one can come up with some kind of alien moss or lichen or some such plant life that lives off ice or sub-surface water to provide the oxygen.

As I said, it's not perfect, but ideal for fictional uses, and I have this little project going on that makes heavy use of the program's results.