Vulcan System Model

A long time ago I made [a post](https://www.reddit.com/r/DaystromInstitute/comments/6l73ez/the_properties_and_details_of_the_bajoran_star/) detailing the Bajoran star system. Here are my thoughts about the Vulcan Star System and the Andorian Star System, which are one and the same.

First of all, we must remember that the Vulcan star is a real star 16 light years away called 40 Eridani, as implied by dialogue in Enterprise and by non-canon word of mouth. This is in fact a ternary system with the main K-type star A, and a double white/red dwarf star.

Why must the Vulcan star and the Andorian star be the same? Consider Weytahn/Paan-Mokar. This dwarf planet from the ENT: Cease Fire is disputed territory between the Andorians and the Vulcans. It is well lit, meaning it must be at least somewhat near a star system, it's not just in interplanetary space.

If it were simply a star system, we would expect that 1) there would be more interesting planets to set up bases on, and 2) one star would belong officially to one of the two powers. The only way I can imagine a dwarf planet could be disputed territory is if the Vulcans and Andorians share a star system, and the dwarf planet orbits both stars. Remember, a base set up by your enemy on Weytahn was compared to a base set up by your enemy on *Pluto*. They had to be in the same system or that analogy would make no sense.

The A/BC component of the 40 Eridani system orbits eachother once approximately every 8,000 years with a distance of approximately 400 astronomical units. The B/C components orbit eachother with a period of 230 years at a distance of 35 au, which is close to the distance between Earth and Pluto.

Now the trouble is, neither B nor C is a very good place to put a habitable planet. B is a white dwarf star, which meant that at one time there must have been a red giant star taking up the habitable zone. C is a M4.5eV red dwarf flare star. Both produce rather a lot of UV, B does so constantly and C does so occasionally. But hey, the Andorians are blue, maybe that means they are reflective in the blue, violet, and ultraviolet, so they can handle the UV. Let's put them around the white dwarf.

This actually makes quite a lot of sense. Andoria's a very cold moon of its gas giant, Andor. Perhaps it's not simply at the cold end of the habitable zone, but really in the freezer! Its heat may mostly come from infrared from the giant planet, and tidal forces producing a huge amount of geothermal energy.

This also means that the position of Weytahn is obvious. It's a dwarf planet of the red dwarf, 40 Eridani C. Still part of the same star system as the Vulcans, but as close to Andoria as Pluto. It even matches the [image of the dwarf planet](https://vignette.wikia.nocookie.net/memoryalpha/images/4/43/Weytahn.jpg/revision/latest?cb=20051205200240&path-prefix=en) with a dim bluish glow on one side and a bright pale orange glow on the other.

But wait a minute. T'pol clearly meant that it was like the *Andorians* had a base too close to the *Vulcans* when she made the Pluto analogy. Perhaps 400 au is still pretty comparable to the distance to Pluto on the scale of interstellar conflict.

It's pretty clear that the Andorians should have more of a right to the system than the Vulcans do in this model, but perhaps the situation is more complicated. We don't know how long the Vulcans and Andorians have been going to space for sure, but I'd wager that Vulcans have been travelling through space for a lot longer. There may have already been Vulcan settlements *in the 40 Eridani C system*. I imagine the Vulcans had a non-interference policy even in the pre-warp days, preventing them from interfering with Andoria, until they invented interplanetary rockets.

So now we know of a few different planetary bodies and we can start to flesh out a system model. Some of these numbers come from observations from the show, some come from real science (Like 40 Eridani's stars and the one known exoplanet) some come from Memory Beta, and I've tried to make sense of it all.

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**40 Eridani A:**

*The parent star of Vulcan, among the closest stars to Earth at only 16 light years.*
Spectral Type: K0.5V
Temperature: 5,300 K
Mass: 0.84 Suns
Radius: 0.81 Suns
Luminosity: 0.457 Suns
Earth-Habitable Distance: 0.676 au.
Color: White-yellow.

**40 Eridani A b / Ket-Cheleb**

*Ket-Cheleb was the first planet to be discovered around 40 Eridani A by humans, in 2018, and by 2019 is the only known planet around the star. (Its name comes from Vulcan I in Memory Beta.) It is incredibly hot, far too hot to sustain life, and has a thick venusian atmosphere. It shines brightly in the dawn and dusk of the Vulcan sky, when it has the decency to show itself at greatest elongation.*
Radius: 1.8 Earths
Mass: 8.47 Earths (real mass of 40 Eridani A b)
Gravity: 2.614 Gee
Density: 8 g/cm^3 (Most of this comes from internal compression, but it's got more iron per volume than Earth does too)
Atmospheric Pressure: 150 atm
Orbit Semi-Major-Axis: 0.22446 au
Orbit Period: 42.378 days
Orbit Eccentricity: 0.04

**40 Eridani A cA / T'khut**

*T'khut is the larger of the two binary worlds making up the Vulcan planetary duo. It has two moons, the minor moon T'Rukhemai (Eye of the Watcher), and the binary companion T'khasi. Its atmosphere is toxic and hot, though somewhat thinner. The planet is volcanic due to interactions between itself, the star, and Vulcan.*
Radius: 1.2881 Earths
Mass: 2.56 Earths
Gravity: 1.543 Gee
Density: 6.60 g/cm^3
Atmospheric Pressure: 0.67 atm
Orbit Semi-Major-Axis: 0.6075 au
Orbit Period: 188.7013 days
Orbit Eccentricity: 0.007
Rotation Period: 74.81 hours.
Angular size from Vulcan: 3.14 degrees.

**40 Eridani A cA I / T'Rukhemai**

*T'khut's minor moon T'Rukhemai is in a ridiculously low orbit, and seems to be a quite dense metal-rich asteroid, either a lucky remnant from the formation of the two planets, or a lucky captured asteroid. Its orbit is perturbed heavily by Vulcan, but not to the point of instability.*
Dimensions: 42km x 35km x 24 km
Density: 6.73 g/cm^3
Orbit Semi-Major-Axis: 23,892 km
Orbit Period: 6.38 hours
Orbit Eccentricity: 0-0.05

**40 Eridani A cB / Vulcan / T'khasi**

*The only habitable planet in the 40 Eridani A system, T'khasi is warmer than Earth, intensely volcanic due to tidal interactions between itself, T'khut, and the star, and covered mostly by deserts. Nonetheless it has some surface water, and plenty of subsurface water as well, and a sentient species of humanoid computers came out of it eventually. Its sun-centric orbit is identical to T'khut's, the orbit numbers below are an approximation for its orbit around T'khut. In reality, the two planets orbit around a common center of mass. Its gravity is higher than Earth's, and it's atmospheric pressure is lower. It can be difficult for humans to keep up, but it's fine for the native Vulcans. The sun is intense on Vulcan, but the air's so thin that even though it's a lot warmer, it can feel comfortable in the shade. The heat mostly comes during the middle of the long day, or anywhere near a volcanically active hotspot. There's no permanent glaciers, but it does get cold enough for frost during the night in the higher latitudes.*
Radius: 1.2 Earths
Mass: 2.0385 Earths
Gravity: 1.416 Gee
Density: 6.5 g/cm^3
Atmosphere Pressure: 0.6 atm
Oxygen Partial Pressure: 0.15 atm
Orbit Semi-Major-Axis: 149,895.3579 km
Orbit Period: 74.81 hours
Orbit Eccentricity: 0.0041
Rotation Period: 74.81 hours

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**40 Eridani B**

*A white dwarf formed from a long dead star, 40 Eridani B is among the less massive white dwarfs, and among the hotter.*
Radius: 0.014 Suns
Mass: 0.573 Suns
Luminosity: 0.013 Suns
Temperature: 16,500 K
Color: Sky-Blue.

**40 Eridani B b / Andor**

*Andor is a large superjupiter orbiting the stellar remnant that was once a red giant star. It is host to several moons, at least including two large earth-mass moons, and has a ring system to boot. Andor's moons were hot water worlds when 40 Eridani B was a red giant, and some Andorian biologists have attributed that hot period to the formation of life on Andor.*
Radius: 11.2 Earths (0.9992 Jupiters)
Mass: 2035.2 Earths (6.4 Jupiters)
Density: 7.87 g/cm^3
Gravity: 16 Gee!
Orbit Semi-Major-Axis: 2.5 au
Orbit Period: 5.221925 years

**40 Eridani B b I / Andoras**

*Andoras is a large water/glacial world orbiting Andor. Its cryotectonic plates move around on a partially exposed surface of water, with geysers and jets occasionally spewing over the surface. It is nearly habitable to Andorians, although its atmospheric pressure is too low and there's only a trace of oxygen.*
Radius: 0.54 Earths
Mass: 0.1366 Earths
Gravity: 0.4684 Gee
Density: 4.78 g/cm^3
Atmosphere Pressure: 0.87 atm
Orbit Semi-Major-Axis: 408,446 km
Orbit Period: 16 hours.

**40 Eridani B b II / Andoria**

*Andoria is a large glacial world orbiting Andor. Its landmasses and seas are both covered by miles of ice for much of its surface, though the equatorial regions are mostly ice free and there are some bare, though snowy, continents and volcanic island chains. Plant life is dark yellow to take advantage of the dim light of 40 Eridani B. Cryovolcanism and volcanism, driven by immense tidal forces from Andoria's parent body, cause hotspots, oases of life in the barren wastes, and popular vacation spots. Andoria's atmospheric pressure is 5.3 atmospheres, mostly nitrogen, argon, and some helium. Oxygen makes up a partial pressure of 0.23 atm, and so they can breathe about as well on Earth. Andor gets only a dim bluish light from its parent star (with enough UV exposure for a serious sunburn if you're not protected), but gets a fair bit of radiant heat from its parent body as well.*
Radius: 0.87 Earths
Mass: 0.5856 Earths
Gravity: 0.774 Gee
Density: 4.9 g/cm^3
Atmosphere Pressure: 5.3
Orbit Semi-Major-Axis: 648,367 km
Orbit Period: 32 Hours.

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**40 Eridani C**

*40 Eridani C is a red dwarf and a flare star, still flashing out bright ultraviolet flares and solar wind with energies that would make the Carrington Event from 1850s Sol blush. Eventually it may calm down, over billions of years of stellar evolution.*
Radius: 0.31 Suns
Mass: 0.2036 Suns
Luminosity: 0.008 Suns
Temperature: 3,100 K
Color: Pale Orange.

**Weytahn / Paan Mokar**

*A dwarf planet (class D Planetoid) around the size of The Moon orbiting 40 Eridani C. Its atmosphere was established by Andorian terraformers, and the dwarf planet is now humanoid habitable. It is also tidally locked to the star, and has an ice cap on one side and is a rocky desert on the oth--oh how fitting.*
Radius: 1821 km
Mass: 0.0135 Earths
Gravity: 0.1652 (Possibly modified with surface gravity plating by terraformers)
Atmosphere Pressure: 0.23-5 atmospheres.
Orbit Semi-Major-Axis: 0.089
Orbit Period: 21.49 days
RotationPeriod: 21.49 days (tidally locked)
Orbit Eccentricity: 0.05