First, we’ll begin by looking at the location of Sadwillow’s star in the Outer Dark Sector.
Now I figure star systems will be named after the most populous inhabited planet in the system, if any such exist, or, failing that, after the most massive star in the system. Sadwillow is more or less earthlike and inhabited, so there you go. The first bit of information I have on this system is that it is binary, so that gives us two stars to name. Let’s go with Cynradd for Sadwillow A and Cydymaith for Sadwillow B. According to Google Translate, those are Welsh respectively for Primary and Companion. Why Welsh? Astrographer’s caprice, actually, but maybe we’ll work in an explanation in the history stage.
I did some of the detailing in GURPS Traveller First In some time ago, so I’ll use that data. I’ll make sure to mention anything that didn’t come out of First In.
As I mentioned previously, this is a binary system according to my First In notes. Both stars are of spectral class G7V, main sequence, yellow stars a little cooler and smaller than the Sun. Sadwillow A, sorry, Cynradd has a mass of about 88% of the Sun(0.879Msol), a luminosity of about 60% of the Sun(0.597 Lsol), a radius of about 83% of the Sun(0.829 Rsol) and a temperature of 5600 Kelvins(5600 K). All of this gives it a main-sequence lifespan of 14.7 billion years. It is described as Old Population I and according to First In it is 4 billion years old. A lot of life left in this one. Speaking of life, since this could be considered similar to Earth about 500 million to 700 million years ago, the land macrofauna might be less than impressive.
From this information, First In gives an inner limit for planet presence of 0.18 au and a lifezone, that is the area where habitable planets might exist, of 0.73 au – 1.0 au. The snowline, the radius beyond which gas giants such as Jupiter are more likely to develop is given as 3.9 au and the outer limit, beyond which planets wouldn’t exist of 35.1 au. Before we go any further on that, we need to look at the companion star and its orbit. For now, just take it on faith that Cynradd won’t have any planets beyond 1.68 au.
As mentioned previously, Sadwillow B, or Cydymaith is also G7V, in this case slightly smaller. Cydymaith has a mass of 0.869 Sols, a luminosity of 0.571 Sols, a radius of 0.811 Sols, a temperature, again, of 5600 K, and a lifespan of 15.2 billion years. Since the two stars were born together Cydymaith will also be 4 billion years old. As calculated by First In, the inner limit will be 0.17 au, the lifezone 0.72 – 0.98 au, the snowline 3.8 au and the outer limit 34.8 au. As with the primary, orbital considerations will limit the outermost orbit of Cydymaith to 1.68 au.
These stars have a moderate separation that comes to 8.4 au. With the eccentricity of 0.4, that comes to a minimum separation of 5.04 au and a maximum separation of 11.76 au. First In assumes that stable orbits exist within a third of the minimum separation of each star and three times the maximum separation of both stars. This gives a forbidden region from 1.68 to 35.28 au. This is beyond either star’s ordinary outer limit for planets, but the combined outer limit is based on the square root of the sum of the stars masses, which comes to 52.9 au. That’s still pretty far out there, so I’m just going to assume there aren’t any planets orbiting both stars.
This topic on the SFRPG forum has given me some concern about the Kozai Mechanism. I’m going to assume the companion star is roughly coplanar with with the planetary orbits, so the inclination of its orbit is about zero.
- I Tanllyd(“Fiery”) – 0.36 au, 1,300 miles diameter, 3.5 g/cm^3, low-iron, 0.104 g, no moons.
- II Sadwillow – 0.76 au, 8,700 miles diameter, 5.7 g/cm^3, medium-iron, 1.13 g, 1 large moon(478,500 mile orbit, 800 mile diameter, 3.5 g/cm^3, 0.144 g).
- III Mawr o Aer – 1.16 au, 60,000 miles diameter, 0.7 g/cm^3, gas giant, 0.96 g, 9 inner small moons(2-5 radii), 3 large moons(7, 9, 11 radii), 5 outer small moons(40 to several hundred radii).
- I asteroid belt Haid Cerrig- 0.51 au, very abundant(+2) asteroid belt.
- II Craig – 0.81 au, 4,800 miles diameter, 4.3 g/cm^3, low-iron, 0.47 g, no moons.
A II Sadwillow
- Semimajor axis – 0.76 au(Insolation: 1.034 times Earth)
- Eccentricity – 0.05
- Perihelion – 0.722 au(Insolation: 1.145 times Earth)
- Aphelion – 0.798 au (Insolation: 0.9375 times Earth)
- Orbital period – 0.7066 year, 258d 2h 40m 10.22s(292.8 local days)
- Rotation period – 21.15 hours, 21h 9m 6.733s
- Solar day – 21.22 hours, 21h 13m 27.670s
- Tidal effects: solar=0.993 lunar=0.0825 E=3.1519 (Need to look up what these are supposed to mean. I think it’s game-specific)
This is what I have so far. We know where we are(well… kinda), and we have a pretty good idea about the size of the planet. That pangaea continent is going to seriously heavy with bigness!