The Galen Alpha Planetary System

This is a write up of the Galen Alpha planetary system, the setting for the Tyranny of the Daleks scenario, using the Second Edition of the Doctor Who Roleplaying Game from Cubicle 7.

The Galen Alpha System

Overview

The Galen Alpha system is a rare and remarkable planetary arrangement found at the extreme fringe of the Milky Way. Orbiting a young, luminous G-type star in near-total isolation, the system has evolved with minimal external disturbance for over three billion years. Its architecture reflects both long-term stability and traces of ancient dynamical upheaval, shaped in part by the distant presence of its companion star, Galen Beta. At its heart lies Galentor, a fertile garden world whose biosphere has given rise to the enigmatic Lentargi field.

A view of the outer reaches of the Galen Alpha planetary system

The Star

Galen Alpha is a G1V main-sequence star with a mass of 1.04 times that of Sol and a luminosity 1.18 times greater. At an age of approximately 3.07 billion years, it is younger and slightly more energetic than Earth’s Sun, emitting a steady gold-white light with relatively subdued magnetic activity.

Its rotation period of 24 days and modest starspot cycle contribute to a calm stellar environment. Combined with the system’s isolation, this has allowed Galen Alpha’s planets to evolve without frequent radiation storms, nearby supernovae, or gravitational disruption. Galen Alpha is orbited at a vast distance of 0.542 light years by its faint companion, Galen Beta, forming one of the widest known stable binary systems.

Inner Dust Ring

A dust ring encircles Galen Alpha between approximately 0.15 and 0.28 AU, composed of hot silicates, carbon-rich grains and scattered metallic fragments.  This is the remnant of a population of early superheated planetesimals that failed to accrete.  

The Planets

The Galen Alpha system contains six major planets, arranged in a broadly classical architecture of inner terrestrials and outer gas giants, though with several distinctive features.

Pentaurus (Galen Alpha b)

A small, rocky inner world orbiting at 0.421 AU. Once partially oceanic, Pentaurus lost most of its volatiles early in the system’s history. It is now a dry, ochre-coloured planet marked by salt flats, deep canyon systems, and scattered geothermal regions.  This planet has one moon, Calyx, which probably originated from impact debris.

Galentor (Galen Alpha c)

The system’s primary life-bearing world, orbiting at 0.969 AU, mostly blue and shining from the oceans to be found on its surface. Galentor is a warm, stable garden planet with low axial tilt and shallow seasonal variation. Roughly three quarters of its surface is ocean, with small, widely distributed continents. Its biosphere is rich and extraordinarily interdependent, supporting forests, oceans, and complex life, including mammalian analogues. The Lentargi field is a planetary-scale bioelectromagnetic phenomenon emerging from this biosphere.

Galentor is orbited by Tarack, an Io-like volcanic moon whose intense activity is driven by tidal interactions within the system.

Karvtal (Galen Alpha d)

A cool, stormy terrestrial world at 1.34 AU. Karvtal is slightly larger than Earth, though less massive due to a lower density, with extensive cloud belts, glaciated regions, and active plate tectonics. Liquid water persists underneath the ice in equatorial, subterranean lakes, and microbial or primitive multicellular life is considered plausible. Karvtal possesses a single satellite, Velnara.

The Cyndor Belt (Inner Asteroid Belt)

The innermost of the Galen Alpha system’s two asteroid belts, this is found between 1.8 and 2.6 AU and is a wide, low-density asteroid region.  It is sparser than the asteroid belt in Earth’s Solar system, and has a low metallicity. 

Thandor (Galen Alpha e)

A cold super-Earth at 3.09 AU, with a mass 3.8 times that of Earth’s. Thandor is transitional between a massive terrestrial planet and a mini-Neptune. A thick ice shell overlies deep subsurface oceans, and a hydrogen-rich atmosphere blankets the surface. Its high obliquity drives extreme seasonal cycles. Thandor, uniquely in the Galen Alpha system, does not have a natural satellite.

Volturn (Galen Alpha f)

The inner gas giant, orbiting at 6.51 AU, and smaller and less massive than Jupiter. Volturn is a pale, mostly copper-coloured, storm-banded giant with a relatively low density and a rapid rotation period. Its early formation acted as a gravitational stabiliser, preventing inward planetary migration and contributing significantly to the long-term order of the system.

Volturn has a faint, pale ring system around it, and nine major moons, along with two small shepherd moons for the rings. It also has 43 inner moonlets, which are really piles of rubble between 1 and 50 kilometres across, and up to 400,000 kilometres distant in their orbit from Volturn.  Finally, there are 59 small moons of between 2 and 80 kilometres across at high inclinations and eccentricities with orbits beyond 1 million kilometres from Volturn, all of which are again little more than piles of rubble bound together with a loose covering of regolith.

Luradian (Galen Alpha g)

The outer gas giant, orbiting at 11.4 AU, slightly longer than the orbit of Saturn around Sol. Larger but less dense than Volturn (and indeed Jupiter), Luradian possesses an extensive and spectacular axial ring system, tilted at 52 degrees, and a dynamically complex moon family, including captured objects and active icy moons. Luradian is subtly coloured, with cyan and pink banding of clouds across its surface. 

Luradian has eleven major moons.  Two of the major moons act as shepherd moons for the ring system, along with seven moonlets embedded in the densest part of the ring, which create wakes and transient spokes during magnetospheric storms.  In addition, a captured icy dwarf planet orbits Luradian at the leading L4 point about Luradian.  Finally there are 58 small irregular moonlets in high inclinations and eccentricities beyond the orbit of the furthest major moon, Vaelor.  These moonlets are from 1 to 40 kilometres across, essentially piles of rubble bound by a loose and thin covering of regolith.  

The Outer Halin Belt

The outermost of the system’s two asteroid belts, this lies between 14 and 22 AU and is a thin, widely spaced belt of icy remains.  It was sculpted by early interactions between Galen Alpha and Beta before the latter was flung far out to 0.542 light years.

Far Objects Zone

Between 30 to 80 AU from Galen Alpha, this sparse and widely spaced zone includes a number of dwarf planets, extremely scattered objects and dormant comet nuclei.  It has a very low density but is deeply ancient compared to the rest of the system.  One body, provisionally named Xyr, displays anomalous spectral lines possibly related to the Lentargi field.

Interactions with the Galen Beta System and Interstellar Space

Galen Beta’s distant orbit has had no significant effect on the stability of Galen Alpha’s planets in the present era. However, early interactions likely shaped the outer debris structures and cleared much of the primordial material beyond the gas giants.

The system’s position at the edge of the galactic disk places it in an exceptionally sparse stellar environment. With no nearby stars, nebulae, or supernova remnants, Galen Alpha has evolved in near isolation. This cosmic quiet has preserved its planetary architecture and allowed Galentor’s biosphere to flourish uninterrupted for billions of years.

To Federation astronomers, the Galen Alpha system stands as a rare natural laboratory. A complete, life-bearing planetary system formed and matured at the very edge of the Galaxy, far from the turbulence of its crowded heart.

The inner Galen Alpha planetary system