Here’s a bit of additional world-building for the Scorpius Reach setting, mostly done with the current draft of Architect of Worlds.

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St. Basil is the fourth planet of the A component of a binary star system. Its primary star is named Emmelia. Emmelia is a typical Population I star, somewhat more massive, hotter, and brighter than Sol. It possesses a substantial family of planets.

Emmelia

• Mass: 1.06 Sol
• Age: 5.7 billion standard years
• Metallicity: 1.0 standard
• Luminosity: 1.63 Sol
• Effective Temperature: 5940 K
• Spectral Classification: G0V

Mazaka (Companion Star)

• Mass: 0.55 Sol
• Age: 5.7 billion standard years
• Metallicity: 1.0 standard
• Luminosity: 0.06 Sol
• Effective Temperature: 3850 K
• Spectral Classification: M0V
• Orbital Radius: 96.8 AU
• Eccentricity: 0.25 (Forbidden zone at 24.2 AU)
• Orbital Period: 750.6 standard years

Planetary System Summary

Planets and other major bodies in the Emmelia star system are named after people associated with St. Basil the Great.

Orbit	Name	UPP	Notes
0.20 AU	Meletius	Y7A0000-0	Tide-locked world with a hot carbon-dioxide atmosphere. No moons.
0.36 AU	Eustathius	Y8A0000-0	Tide-locked world with a hot carbon-dioxide atmosphere. No moons.
0.62 AU	St. Macrina	Y600000-0	Hot airless world. No moons.
1.28 AU	St. Basil	C645456-8	Primary world in the system, with a thin but breathable oxygen-nitrogen atmosphere tainted by biotoxins, a moderate amount of liquid surface water, and a temperate climate. Colony world. No moons.
1.85 AU	St. Gregory	Large GG	Spectacular ring system. One large moon, many moonlets.
3.83 AU	St. Petros	Medium GG	Moderate ring system. Two large moons, several moonlets.
7.17 AU	St. Naucratius	Small GG	Moderate ring system. One large moon, several moonlets.
11.61 AU	Julianos	YAA0000-0	Dense, bitterly cold hydrogen-helium atmosphere. No moons.

St. Basil

St. Basil is a marginally habitable world. It has a pleasant climate in limited regions of the surface, but the local ecology is somewhat incompatible with human biochemistry and airborne toxins are common.

Orbital and Rotational Parameters

• Orbital Radius: 1.275 AU
• Orbital Eccentricity: 0.08
• Orbital Period: 12260 hours
• Rotation Period: 21.50 hours
• Local Day: 21 hours, 32.5 minutes
• Local Year: 569.13 local days
• Obliquity: 24° (unstable)
• Satellites: None

Mass and Surface Gravity

• Mass: 0.47 Earth
• Density: 0.92 Earth (5.08 g/cc)
• Radius: 5090 km
• Surface Gravity: 0.74 standard

Geophysics

• Geophysical Parameters: Mature plate lithosphere with mobile plate tectonics
• Magnetic Field: Strong
• Hydrographic Coverage: 50%

Atmosphere

• Surface Atmospheric Pressure: 0.69 atm
• Atmospheric Components (by Mass):
  • Nitrogen 75.5%
  • Oxygen 22.3%
  • Carbon Dioxide 0.4%
  • Argon 1.0%
  • Water Vapor 0.3%
• Atmospheric Scale Height: 11.6 km
• Atmospheric Classification: Thin, tainted (low oxygen content, seasonal airborne toxins in regions of plentiful native vegetation)

Climate

• Blackbody Temperature: 279 K
• Bolometric Albedo: 0.27
• Total Greenhouse Effect: 31 K
• Average Surface Temperature: 289 K

Native Life

• Age of Advanced Biosphere: 1.71 billion standard years
• Dominant Life Forms: Sophisticated animals, both aquatic and land-based, including several pre-sentient species
• Biochemical Compatibility: Poor

Human Habitation

• Human Population: 50,000
• Founder Groups: Eosi (100%)
• Government Type: Feudal Technocracy
• Law Level: 6
• Starport Class: C (Routine facilities, repair yard for small ships)
• Base Facilities: Scout base
• Local Tech Level: 18
• Trade Classifications: Non-Industrial

Notes

St. Basil is notable for its proximity to the massive gas giant planet St. Gregory. St. Basil and St. Gregory are in a stable 7:4 orbital resonance. While the gas giant’s influence stabilizes St. Basil’s orbit, it also causes the smaller planet’s rotational axis to undergo wild excursions over million-year timescales.

St. Basil is currently recovering from a mass extinction which apparently took place about two million years ago. The largest native land animals are about the size and sophistication of a domestic cat. The history of life on the planet is full of such incidents – the variability of the planet’s rotational axis means that its climate is also extremely unstable over long periods.

Native life on St. Basil is biochemically incompatible with Earth-derived life – the two can usually obtain no nutritional value from one another, and the very attempt is likely to provoke serious allergic or toxic reactions. Even the native plant life is prone to give off airborne toxins that can lead to serious illness or even death in Earth-derived animal life. The St. Basil colony tends to expand its territory by burning the native ecology to the ground, plowing the resulting carbon under, and then introducing Earth- or Eos-derived life forms. Humans venturing away from the protected colony are advised to wear filter masks and carry supplemental oxygen.

St. Basil was originally colonized in 2403, by founder groups of Chinese and Japanese origin. The original name of the colony was Guang. The Guang colony failed slowly after the Silence, with all human inhabitants deceased by 2600. The planet was rediscovered in 2833 and recolonized from Eos in 2840. St. Basil is currently organized as a semi-autonomous province of the Kingdom of Eos, ruled by a consortium of technical and scientific experts, with support from the Kingdom’s interstellar navy and scout service.

The local economy is more or less self-sufficient at a TL8 level. It is centered around scientific study of the native biosphere, which promises to produce a variety of useful pharmaceuticals. Prospectors have also recently discovered prodromoi remnants on the planet.