Working on Tau Ceti for ArcBuilders

[Dollan]

Hi guys...

I'm working on an upgrade to my existing Tau Ceti add-on. I'm only just writing the ssc file right now, but I was wondering if there would be any interest in a description of the planets at all, or just the information that pertains to the ssc file. In other words, do you guys want to hear about why such and such a planet is the way it is, what might be found there, etc., or shall I just post the ssc file when I get it done?

This is assuming that there is even any interest at all

...John...

[eburacum45]

I would be interested in a description of the changes or improvements, for instance how you have altered the world from the original version and any new techniques you have used in making the textures. Have you been using any technique to eliminate polar pinch, for instance?

[Dollan]

Hey Steve...

Yeah, polar pinch is a real problem with me, but the best method that I've found so far is to transform the map into polar coordinates, and smooth out the pinched regions, or even clone from an unaltered copy to the pinched regions. Depending on how careful I am, I've gotten results that range from barely passable to downright excellent.

As for changes from the original, I'm planning on decreasing the number of planets, reflecting the star's lower mass and its much lower metallicity. There will be two terrestrial worlds in the inner system region, Thoosa and Glaucus (the latter of which is indigenously named Igom). Next out will be an asteroid belt, but with an empty region in the middle, where the double planet Scylla and Charybdis orbits. From a distance, I hope to make it so that the gap looks similar to the old view of Saturn's Encke Gap. Beyond this is the gas giant Phorcys (I've been assuming that the presence of an asteroid belt is indicative of a gas giant in the "next orbit out", as it were. Finally, there will be the thickened Kuiper belt, centered on 55 AU's distance. But the inner region of the belt will be thinner and stretch inward for some distance. I'm not sure how well this will represent the recent discovery of Tau Ceti's thickened Kuiper belt, though....

I'll be making the asteroid belts using Cormoran's wonderful and simple belt maker utility, but it will probably take a few times to tweak the belts enough to get the visual look that I'm hoping for.

...John...

[Dollan]

Here are a couple of screen shots of the inner and outer Messia asteroid belts. From above they look great, but using Cormoran's asteroid generator, I can't give them an inclination less than 15 degrees.



Here is a shot from the plane of the eccliptic (roughly), demonstrating the thickness of the belts. The highlighted orbit, in each image, is that of the double planet Scylla and Charybdis. My intention was to have had the double body as the device to clear out a gap in the belt.



Anyway, thoughts?

...John...

[bdm]

The asteroid belt has a few realism issues.

First, the orbits asteroids have unrealistic eccentricities. Real asteroids have orbits whose eccentricities follow a Rayleigh distribution peaking at about 0.14. This isn't occurring in the asteroids given here. The action of the embedded planet will act to perturb the orbits, so even if the orbits start out circular they won't remain so.

Second, the mechanism by which asteroids get cleared out of orbital zones also creates gaps in the distribution of orbital periods called Kirkwood gaps. These gaps are not evident in the asteroid orbits.

Third, the inner edge and outer edge of the exclusion zone is too far from the neighbouring planets, particularly the outer edge.

I hope you don't mind the criticism, but I'm assuming you want your system to be as realistic as possible.

[Dollan]

Hi bdm...

No, I certainly appreciate and welcome the criticisms! I am trying to make as realitic as possible a system, and these belts are by far the most difficult part of the whole process.

The program that I'm using to make the belts is somewhat limited, although it does serve as a "quick fix". I did try to use your program, but my experience with Excel is virtually nil, and so I was quite lost. A failing on my part.

So what might you reccomend, if I could ask, in the way of general layout? The imbedded planet, as I have it right now, is thus:

Code: Select all

"ScyllaCharybdis" "Tau Ceti"

   {
   Class      "Invisible"
   EllipticalOrbit
      {
      Period      3.4
      SemiMajorAxis   2.35
      MeanLongitude   10
      }
   }

"Scylla" "Tau Ceti/ScyllaCharybdis"

   {
   Class      "Planet"
   Texture      "Scylla.jpg"
   BumpMap      "Scylla-bump.jpg"
   BumpHeight   1.0
   Radius      4758
   # Mass      0.373
   # Density      0.2164
   EllipticalOrbit
      {
      Period      1.069375
      SemiMajorAxis   2013.071
      Eccentricity   0.0036
      Inclination   26.72
      MeanLongitude   0
      }
   RotationPeriod   25.665
   Obliquity      26.72
   Albedo      0.55
   }

"Charybdis" "Tau Ceti/ScyllaCharybdis"
   
   {
   Class      "Planet"
   Texture      "Charybdis.jpg"
   BumpMap      "Charybdis-bump.jpg"
   BumpHeight   1.0
   Radius      3116
   # Mass      0.093 # Earth masses.
   # Density      0.9487
   EllipticalOrbit
      {
          Period      1.069375
      SemiMajorAxis   8073.929
      Eccentricity   0.0036
      Inclination    26.72
      MeanLongitude   180
      }
   RotationPeriod   25.665
   Obliquity      26.72
   Albedo      0.35
   }

They are not large worlds, obviously, but I'm sure that they would have a major effect on the belt?

...John...

[bdm]

Fascinating, your double planet is remarkably like one I have created for my Canopus Sector series of systems. Yours is a little larger (4758 and 3116 versus 4474.2 and 2957.1) and yours orbits closer than mine.

Comparing your planet to mine, you may have made a mistake with your orbital parameters for your double planet. If you were to use the given orbital parameters to derive the density of those worlds, you would find that the densities of your worlds falls below that of water. When I have access to my spreadsheets I can calculate the masses and densities of your worlds.

My larger world:
# Density 4.62
# Mass 0.2902 Earth masses
# Gravity 0.5893 g

My smaller world:
# Density 3.75
# Mass 0.0680 Earth masses
# Gravity 0.3161 g

[Dollan]

Fascinating, your double planet is remarkably like one I have created for my Canopus Sector series of systems. Yours is a little larger (4758 and 3116 versus 4474.2 and 2957.1) and yours orbits closer than mine.

I have a soft spot for set ups such as this. In some later, planned systems I have much less realistic double systems, but I find that sometimes the visual effect that they create far outweighs the problems that they might have with reality. At any rate....

Comparing your planet to mine, you may have made a mistake with your orbital parameters for your double planet. If you were to use the given orbital parameters to derive the density of those worlds, you would find that the densities of your worlds falls below that of water. When I have access to my spreadsheets I can calculate the masses and densities of your worlds.

I'm assuming that these are rather icy bodies, considering their distances from what is an intrinsically dimmer sun, but I couldn't say for certain, not knowing where the snow line falls in the Tau Ceti system. At any rate, I'd love any help that you can give me! I had a devil of a time getting these things to orbit so that one side faces the other all of the time, and if I remember correctly it was Spaceman Spiff that finally came up with the parameters for me.

I have a blast designing these systems, but I'm afraid that I am absolutely horrid when it comes to the hard math to do it properly....

...John...

[Malenfant]

I'm assuming that these are rather icy bodies, considering their distances from what is an intrinsically dimmer sun, but I couldn't say for certain, not knowing where the snow line falls in the Tau Ceti system.

The Frost Line for Tau Ceti would be at 1.94 AU at its current luminosity. When it first formed it would have been closer to 1.3-1.5 AU probably as it was less luminous in the past.

[bdm]

Yes, there are obvious errors in the density, orbital separation and the like.

# Density 0.2164
# Density 0.9487

These are incorrect. To get orbital periods that are in the vicinity of 1 day with the given orbital separations, the densities must be reduced to between 0.1 and 0.2. For ice bodies, this is too low.

For ice bodies, the density must be between 1 and 2. It's reasonable to suppose that the ice bodies will have rocky cores, and this increases the density to greater than 1.

If the densities are 1.5 and the bodies have the same diameters as now, here are representative figures:

Both bodies:
Period: 0.306287 d (7.350894 h)

Body 1:
Density: 1.5
Mass (kg): 6.768E+23
Mass (Earths): 0.1133
Surface Gravity: 0.2035 g
Semimajor axis: 2211.938 km

Body 2:
Density: 1.5
Mass (kg): 1.901E+23
Mass (Earths): 0.0318
Surface Gravity: 0.1332 g
Semimajor axis: 7875.062 km

I can give you another spreadsheet created specially for determining the orbital elements for a binary planet. It's not of release quality, but I can polish it a little so it's clearer what's going on.

[Michael Kilderry]

Weren't there originally no gas giants in the original ArcBuilders Tau Ceti system? Why did you decide to add one in?

[Dollan]

Thanks for the information, bdm, Malenfant. I'll put it all to good use later today, and post a preliminary layout of the system as a whole. And bdm, anything you have that can help with this stuff, would be much appreciated!

Malenfant, how does one determine the snow line for a given star?

Michael... the original 0.1 release of Tau Ceti had, I think, at least two Jovians, and probably three. In this release, I'm making it only one Jovian, with much of the outer system taken up by increased minor bodies.

...John...

[Dollan]

Here is the ssc file for the Tau Ceti System thus far. Please note that I have not yet corrected the errors pointed out by bdm for Scylla and Charybdis.

Code: Select all

"Thoosa" "Tau Ceti"

   {
   Class      "Planet"
   Texture      "Thoosa.jpg"
   Radius      3568.24
   HazeDensity   8.0
   HazeColor   [ 0.72 0.33 -0.01 ]
   Atmosphere
      {
      Height      400
      Lower      [ 0.57 0.32 0.03 ]
      Upper      [ 0.77 0.94 0.05 ]
      Sky      [ 0.86 0.80 0.56 ]
      Sunset       [ 0.83 0.57 0.18 ]
      CloudHeight   60
      CloudSpeed   120
      CloudMap      "Thoosa-clouds.png"
      }
   EllipticalOrbit
      {
      Period      0.09
      SemiMajorAxis   0.21
      Eccentricity   0.00
      Inclination   0.897
      }
   RotationPeriod   32.85
   Obliquity      7.01
   Albedo      0.6
   }

"Glaucus (Igom)" "Tau Ceti"

   {
   Class      "Planet"
   Texture      "Igom.jpg"
   BumpMap      "Igom-bump.jpg"
   BumpHeight   4.5
   SpecularTexture   "Igom-spec.jpg"
   SpecularColor   [ 0.5 0.5 0.55 ]
   SpecularPower   20.0
   Radius      5993.5
   # Mass      
   HazeDensity   0.3
   Atmosphere
      {
      Height       100
      Lower       [ 0.24 0.46 0.75 ]
      Upper       [ 0 0.41 1 ]
      Sky       [ 0.50 0.87 0.97 ]
      Sunset       [ 0.89 0.65 0.51 ]
      CloudHeight    15
      CloudSpeed    45
      CloudMap    "Igom-clouds.png"
      }
   EllipticalOrbit
      {
      Period      0.624
      SemiMajorAxis   0.68
      Eccentricity   0.0167
      Inclination   0.000
      }
   RotationPeriod   29.458
   Obliquity      3.45
   Albedo      0.36
   }

"Labicus (Isik)" "Tau Ceti/Glaucus (Igom)"

   {
   Class      "Moon"
   Texture      "Isik.jpg"
   BumpMap      "Isik-bump.jpg"
   BumpHeight   2.0
   Radius      2816
   EllipticalOrbit
      {
      Period      25.35
      SemiMajorAxis   362450
      Eccentricity   0.0782
      Inclination   26.354
      }
   RotationPeriod   111.457
   Obliquity      3.45
   Albedo      0.12
   }

"ScyllaCharybdis" "Tau Ceti"

   {
   Class      "Invisible"
   EllipticalOrbit
      {
      Period      3.4
      SemiMajorAxis   2.35
      MeanLongitude   10
      }
   }

"Scylla" "Tau Ceti/ScyllaCharybdis"

   {
   Class      "Planet"
   Texture      "Scylla.jpg"
   BumpMap      "Scylla-bump.jpg"
   BumpHeight   1.0
   Radius      4758
   # Mass      0.373
   # Density      0.2164
   EllipticalOrbit
      {
      Period      1.069375
      SemiMajorAxis   2013.071
      Eccentricity   0.0036
      Inclination   26.72
      MeanLongitude   0
      }
   RotationPeriod   25.665
   Obliquity      26.72
   Albedo      0.55
   }

"Charybdis" "Tau Ceti/ScyllaCharybdis"
   
   {
   Class      "Planet"
   Texture      "Charybdis.jpg"
   BumpMap      "Charybdis-bump.jpg"
   BumpHeight   1.0
   Radius      3116
   # Mass      0.093 # Earth masses.
   # Density      0.9487
   EllipticalOrbit
      {
          Period      1.069375
      SemiMajorAxis   8073.929
      Eccentricity   0.0036
      Inclination    26.72
      MeanLongitude   180
      }
   RotationPeriod   25.665
   Obliquity      26.72
   Albedo      0.35
   }

"Phorcys" "Tau Ceti"

   {
   Class      "Planet"
   Texture      "Phorcys.jpg"
   NightTexture   "Phorcys-night.jpg"
   Radius      51395
   # Mass      89.1xEarth (0.28xJove)
   EllipticalOrbit
      {
      Period      15.1845
      SemiMajorAxis   6.132
      Eccentricity   0.012
      Inclination   3.65
      }
   Atmosphere
      {
      Height      100
      Lower       [ 0.99 0.38 0.15 ]
      Upper       [ 0.94 0.94 0.69 ]
              Sky       [ 0.88 0.54 0.03 ]
              Sunset       [ 0.98 0 0.02 ]
      }
   RotationPeriod   13.24
   Obliquity      12.874
   Albedo      0.51
   Rings
      {
      Inner      72100
      Outer      136050
      Texture      "Phorcys-rings.png"
      }
   }

"Xxx" "Tau Ceti/Phorcys"

   {
   Class      "Moon"
   Texture      "Xxx.jpg"
   BumpMap      "Xxx-bump.jpg"
   BumpHeight   1.0
   Radius      2378
   EllipticalOrbit
      {
      Period      4.588
      SemiMajorAxis   523600
      Eccentricity   0.012
      Inclination   3.524
      }
   RotationPeriod   317.76
   Obliquity      0.06
   Albedo      0.34
   }

There are also a couple of other unfinished features, including some planet and/or moon names, as well as the planned asteroid belts and Kuiper belts.

...John...

[Dollan]

Here are a couple of shots for the first planet in the system, Thoosa. My idea behind it is a world, very hot, with a surface continually buffeted by sand storms and high winds. However, its atmosphere is Venus-like in that it is quite thick. But, due to its being a smaller world, its atmosphere is not as thick as Venus', so perhaps solar heating has as much to do with the planetary warming as the atmosphere, if not more so.

At the moment, I'm not too keen on this texture, nor on its accompanying bump map. The image turned out to be a bit low res for my tastes, even though I generally hold myself to 1024x2048. In the end, I may well chuck it and try for something else. And that's not assuming that I would have to if the physics of the planetary environment turn out to be untenable.

Anyway, here are the shots, minus the planetary cloud layer (which I haven't made yet anyway). Oh, I also ramped up the haze layer on this world as well, to a wonderful 8.0! With its decidedly red cast, I rather like the look of it, coupled with the far-reaching, thick atmosphere. Now to just make the clouds to match....





...John...

[Michael Kilderry]

Michael... the original 0.1 release of Tau Ceti had, I think, at least two Jovians, and probably three. In this release, I'm making it only one Jovian, with much of the outer system taken up by increased minor bodies.

...John...

I looked at the old Tau Ceti addon just now, and there are no gas giants, only small rocky worlds, you might be thinking of another addon.

Planet Thoosa looks good so far, but it would be nice if you made the texture look a bit more hi res.

[Dollan]

No gas giants at all, eh? I must have changed something from the old sketches that I have....

At any rate, the resolution problem is indeed what I was thinking of for Thoosa. I might spend today trying to come up with something new.

...John...

[Dollan]

Alright, here is my new take on Thoosa, the nearest planet to Tau Ceti (at some 0.21 AU).

This is the planet as it appears normally, wrapped within its thick cloud layer. Essentially, it is a generic Titan texture, tweaked just a bit to match the atmospheric and haze color that I gave the planet itself.



Here is Thoosa minus the clouds. I lowered the haze density a bit, which was making the planet appear less sharp than what it truly was. However, it is still somewhat muted, even with a bump map. Viewed here is a neat trench running along the hemisphere of the planet. Perhaps the last refuge of volcanism on this planet?



Here is the opposite hemisphere. The reddish haze is very obvous in this view.



Well, that's Thoosa. I'll probably give this planet a rest for the moment, unless anyone has any major recomendations.

...John...

[ajtribick]

As far as I've been able to figure out, the snowline is taken to be where the temperatures reach 170K, though this source indicates that it might need to be colder, at 145K.

Taking the parameters of Tau Ceti given in Celestia, and working backwards to get 1.94 AU, and assuming the 170K limit, I'm guessing Malenfant is using an albedo of 0.1 for the calculation.

[Malenfant]

Taking the parameters of Tau Ceti given in Celestia, and working backwards to get 1.94 AU, and assuming the 170K limit, I'm guessing Malenfant is using an albedo of 0.1 for the calculation.

I didn't - I used the blackbody equation but assumed the frost line was at 175K instead of 170K. Albedo was assumed to be 0.0.

[ajtribick]

Well, I was close