PlutonianEmpire's Worldbuilding Thread

Greetings.

For a number of years now, I've been working on a planet named Belle Hades, orbiting Delta Trianguli. (I'll try not to upstage NuclearVacuum... ).

For a while now, I've had Belle Hades rendered in Celestia as a planet with blue skies, since it is a habitable Earthlike world, smaller than Earth. When I read the "Sky Colors on Alien Worlds" page on Orion's Arm, I figured that the second sun, Delta Trianguli B, would influence the sky colors depending on whether it was first to rise or last to set, considering it is probably a star of spectral class K. In Celestia, I've defined it as a K3V.

The sky color I assumed Delta Tri B would give Belle Hades during sunets/sunrises was lavender (RGB: 181, 126, 220), considering that Delta Tri is a close binary, with the Primary being a G0V, as I render it in Celestia.

However, I do have my doubts whether the sky and sunset colors I have set would be any accurate, so I've come to you for help.

Delta Trianguli
System Type: Close Binary Star
Distance: 35.2 Light years
Orbital Separation: 0.106 AU (15,857,374.2942 km / 9,853,315.5709 miles)
Orbital Period: 10.0201 Earth Days
Age: 1.9 billion Earth years
Habitable Zone: 1.06659 AU (159,560,698 km / 99,146,421 miles)
Number of Planets: 1
Number of Asteroid/Kuiper Fields: 1

Lilith (Delta Trianguli A, Primary):
Spectral Type: G0V
Mass: 1.09x Sol
Luminosity: 1.12x Sol
Diameter: 0.98x Sol
Temperature: 6,030° Kelvin (5,757° C / 10,394° F)
Rotation Period: 4.96 Earth days
Apparent Magnitude: 4.83 - 4.87
Distance from Barycenter: 0.043 AU (6,463,603.6525 km / 4,016,297.1077 miles)
Individual Habitable Zone: 1.0587 AU (158,385,928.72 km / 98,416,453.362 miles)

Hades (Delta Trianguli B, Secondary):
Spectral Type: K3V
Mass: 0.75x Sol
Luminosity: 0.18x Sol
Diameter: 0.74x Sol
Temperature: 4,730° Kelvin (4,457° C / 8,054° F)
Rotation Period: 3.79 Earth days
Apparent Magnitude 6.83 - 6.87 (2.00 magnitudes dimmer than Lilith)
Distance from Barycenter: 0.063 AU (9,393,770.6417 km / 5,837,018.4632 miles)
Individual Habitable Zone: 0.4215 AU (63,054,570.83 km / 39,180,293.852 miles)

Physical Properties:
Diameter: 10,939.2924 km (6,797.3612 miles; 0.8576x Earth)
Mass: 0.6054x Earth
Density: 0.96x Earth (5.2944 g/cm3)
Gravity 0.8233x Earth
Escape Velocity: 9.397 km/s (5.839 mile/s)
Sidereal Rotation Period: 26 hours, 26 minutes, 54 seconds
Day Length: 26 hours, 32 minutes, 49 seconds (based on when the Barycenter reaches zenith)
Axial Tilt: 26.4052°

Orbital Properties:
Orbital Distance: 1.066597 AU (159,560,698.96 km / 99,146,421.74 miles) (Middle of HZ)
Year Length : 296.3975 Earth Days (268.9602 local days)
Eccentricity: 0.0119
Inclination: 1.4662°
Ascending Node: 313.9975°
Argument Of Pericenter: 324.2635°
Mean Anomaly: 177.8046°

(The Inclination, Ascending Node, Argument Of Pericenter, and Mean Anomaly are all relative to the plane of Lilith's and Hades' orbits.)

Atmosphere:
Surface Pressure: 1.059x Earth (107.303 kPa; 31.69 barometric inches).
Composition: 69% Nitrogen, 27% Oxygen, 0.82% Argon, 0.029% Carbon Dioxide, 3% water vapor.

With these charactaristics, what are the best sky and sunset colors for Belle Hades?

Thank you for your time, and it is nice meeting you.

~ PlutonianEmpire

Good question. I've done a look into sky colours: as you go to later spectral types the star's spectrum and Rayleigh scattering act more in opposite directions, so I reckon the sky gets paler.

On the other hand this doesn't really help for what happens at sunset.

Maybe worth looking into writing an implementation of Bruneton and Neyret "Precomputed Atmospheric Scattering" (pdf) - the focus there is on realtime rendering, but it looks like it can be adapted for this task.

Incidentally why use a spoiler tag there?

Ah, thank you.

The spoilers were due to my habit of using them to make my posts appear less of a wall of text/less "too long; didn't read", in an attempt to be more considerate.

I can remove the spoiler tags if you want.

Hi, I changed the thread title, because I didn't want to clutter the subforum with questions about the same planet and system.

Anyways, new situation: Belle Hades has two moons. The way I currently have it set up, the first moon was formed by a collision similar to the one that Earth experienced and got a moon from. The first moon, Tartarus, is about 41% the size of Belle Hades. The second moon, Lethe, is a captured object, is about 24% the size of Belle Hades, and is the inner moon. Each have eccentricities less than 0.016

I tested the original system in a gravity simulation program a few times, and Lethe would either crash into the planet, or would crash into the bigger moon. Increasing Tartarus' orbit a bit fixed the problem, and the system was stable with the following stats:

Lethe:
Diameter: 2,652.4252 KM (1,648.1406 miles)
Mass: 0.005454x Earth
Density: 0.6067x Earth (3.346 g/cm3)
Distance: 98,304.3782 km (61,083.5087 miles)
Orbital Period: 4 days, 12 hours, 43 minutes, 12 seconds

Tartarus:
Diameter: 4,516.5936 km (2,806.4812 miles)
Mass: 0.027646x Earth
Density: 0.62283x Earth (3.424 g/cm3)
Distance: 316,172.3226 km (196,460.3731 miles)
Orbital Period: 25 days, 11 hours, 2 minutes, 24 seconds

My question is, what ways would the planet/moon system reasonably get to this state in the first place? If there isn't, what would be a more realistic way to set up the two large moon system and a way to get to that point?

I'm not sure how a terrestrial planet would be fortunate enough to get two large moons. Ours came from a massive impact but then we had to wait four billion years for it to move far enough away for room for another (though, if I understand right, our Moon is too massive to permit another moon for astronomically long periods of time). You might be able to capture a moon but it's tricky to do.

I'm going to go out on a limb and say terrestrial planets with multiple large moons are going to be very rare.

I did state that Lethe was a captured object. The capture scenario I imagined in my mind would be that Lethe was originally a planet with an eccentric orbit, intersecting Belle Hades', and eventually, Lethe passed through Belle Hades' roche limit, and on its way out, wound up coming up behind Tartarus. The encounter with Tartarus ensured the capture of Lethe, and gave Tartarus a higher orbit, and after additional interactions, settled in their current orbits.

Is this a feasible scenario, or are there any other capture scenarios that might be feasible? Or would it be better to have a single-moon system?

If anyone wants the full info for my version of Delta Tri, the page I have on the system is here:

http://freewebs.com/theplutonianempire/bellehades.htm

All the important numbers are on the first half of the page. The rest is just textual details and images.

Is there anything that you suggest I modify?

Based on recent info detailed in this thread , is the potential habitability of terrestrials surrounding Delta Trianguli influenced in any way by the new info, considering the companion star to be Late-G or Early-K (K3V, as I've detailed it for my version of this system)?

How does one go about calculating the height of a terrestrial world, given the surface pressure, surface gravity, and temperatures? (Or should I look at different factors?)

I think this site will be helpful for you.
http://en.wikipedia.org/wiki/Scale_height

Actually it is, although it is admittedly more info than I anticipated. What I'm looking for is to figure out how to visualize an atmosphere when rendering it in Celestia (eg, how high or low I should set the height values for a given world). I know the gravity and temperature parts, although I do find the molecular mass and pressure portions a bit difficult to figure out.

Right now, I'm working on a circumbinary system surrounding an A0V main-sequence star with an F6V main-sequence companion. (Specifically, I'm adding a fictitious companion to HD 140331.)

My question is, what would be the best way to calculate the habitable zone for this admittedly short-lived system? (An example scenario would be terraforming a large planet or moon in the the system's combined HZ, for an emergency, temporary home after aliens suffer a homeworld demise around a neighboring system, because no other star is closer.) What I've been trying to do is figure out what the bolometric and ultraviolet magnitudes would be, since Celestia uses just visual light when reading the AppMag and AbsMag values in STC files.

When adding up the two stars, do I add the temperatures of the two stars together as well as their luminosities and masses, so I can take the bolometric luminosities into account? Or something else?

Define "best".

You need to decide what kind of tradeoffs between ease of calculation and accuracy you want to make.

Simplest method is to add the total bolometric fluxes and set the distance to each star equal to the distance to the barycentre, which is reasonable provided the planetary orbit is much wider than the binary. Adding in factors such as varying distance to the stars, eclipses, N-body effects on the orbits will require more detailed calculation.

Maybe this would be interesting for you?

Müller and Haghighipour "Calculating the Habitable Zone of Multiple Star Systems"
http://arxiv.org/abs/1401.0601

and the associated interactive website
http://astro.twam.info/hz/

Looks exciting, will check it out; thanks!

Going back to the atmosphere scale heights thing, does the surface pressure of a planet's atmosphere influence or modify the scale heights at all? If so, how would I go about including the surface pressure in my calculations?

I might have interpreted it wrong, but the wiki article provided by sirius_alpha seemed a bit vague on that, at least to me. Right now, i just get my scale heights as

(1.380648813e-23 * mean temperature kelvin) / ((mean molecular mass in kg * 1.66053892173e-27) * surface gravity m/s^2) = scale height in meters.

Any way I can include an arbitrary surface pressure in that?

I just thought of something...

I know that some objects in the Solar System seem to have locked themselves into stable or semi-stable long term orbital resonances. When I was observing a system in an extremely old Celestia addon from a former Celestian which I updated with the latest features of 1.6.1 and newer science and observation data, in Errai (Gamma Cephei), when the outermost planet of star A, with a SMA a bit too far for stability, almost seemed to move in tandem with star B when I increased the timescales.

This had me wondering, since off the top of my head, a similar situation exists with Pluto, in resonance with Neptune, might it be possible for large asteroids or even small planets (or even bigger), to potentially end up locked into orbital resonances involving a companion star or brown dwarf in medium-wide binaries in any range of eccentricities?