A write-up of the Galen Beta system from Tyranny of the Daleks. This is for the second edition rules for the Doctor Who Roleplaying Game from Cubicle 7.
Galen Beta is the faint, compact, and ancient-seeming red dwarf companion to Galen Alpha. Although both stars formed together, Beta matured into one of the smallest possible true stars, shining only faintly in the deep interstellar dark far beyond the crowded spiral arms. Its remote orbit, extreme stellar density, and austere planetary system make it one of the strangest known systems in this region of space.
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| Galen Beta, seen at a distance of around 500,000 kilometres and in the distance Lethion at around 1.4 AU, and Galen Alpha about half a light year away |
Spectral type: M9V main-sequence star
Mass: 83.3 x Jupiter or 0.0795 Solar mass
Radius: 1.18 x Jupiter (86,500 kilometres)
Density: 67.2 g/cm3 (Fifty times that of Jupiter)
Luminosity: 5.15 x 10-4 x Sol
Surface temperature: 2500 K
Age: 3.07 billion years
Rotation period: 15.1 days
Distance from Galen Alpha: 0.542 light years (semi-major axis)
Orbital period around Galen Alpha: 5,980,000 years
Surface Gravity: 1.48 km/s2 (roughly 150 times the surface gravity of Earth)
Obliquity: 14.3 degrees to orbital plane
Orbital Eccentricity: 0.345
Orbital Inclination: 12.2 degrees
Galen Beta represents the practical minimum mass at which hydrogen fusion can occur. Its radius barely exceeds that of Jupiter, but its density is fifty times that of the gas giant, reflecting the intense compression of matter in the lowest mass main-sequence stars.
Despite its small size, it is a fully fledged star. Its faint light is a deep ruby red, and its luminosity is only five ten-thousandths that of Earth’s Sun. Even planets in close orbits receive very little energy, creating a cold and unwelcoming system. Most of its radiation is in the infra-red rather than visible light.
Formation
Galen Beta formed from the same primordial cloud that created Galen Alpha, but the environment in this sparse region of the galaxy slowed star formation considerably. The initial material was thin and irregular, producing two protostars with very uneven masses. Galen Beta was deprived of much of its potential accretion by the rapidly growing Galen Alpha, which absorbed most of the available matter from the shared protoplanetary disc.
Beta therefore emerged as a borderline red dwarf that very nearly became a brown dwarf. The early gravitational interactions between the two forming stars sculpted and disrupted the material around them, leaving Galen Alpha with a much richer planetary system and Galen Beta with only a small inner disc of debris from which a handful of close-orbiting planets later condensed.
It is believed that Galen Beta originally formed much closer to Galen Alpha and then following formation, its orbit increased slowly over millions of years to the far range that it has now. This movement affected the development of Galen Alpha’s planetary system.
Because the two stars orbit at great distance, tidal effects after formation have been negligible. Galen Beta’s eccentric orbit through the deep interstellar medium has, however, gently perturbed the outer debris populations of both systems over billions of years.
The Galen Beta Planetary System
Galen Beta possesses a small, compact but scientifically fascinating planetary system consisting of three terrestrial-class planets (one of which is a super-Earth) and one mini-Neptune, all orbiting close to the star. The outermost planet, the gaseous mini-Neptune named Lethion, orbits Galen Beta at a distance of approximately 1.4 AU, roughly the same distance as Mars does Sol. All Beta-worlds are extremely cold due to the star’s minuscule luminosity.
Beyond the planets lies a broad and sparse cold debris belt from roughly 2.2 to 6 AU, a remnant of early disc fragmentation and later sculpting by the distant gravitational influence of Galen Alpha. The belt is extremely cold and sparsely populated. It acts as a long-term reservoir for cometary bodies that occasionally wander inward over multi-million-year cycles.
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| The Galen Beta planetary system, including the two terrestrial planets Eryndra and Kelthar nearest the star, the super-Earth Dravis and the mini-Neptune gas planet Lethion. |
Appearance from Galentor
From Galentor, Galen Beta shines as a faint red star on clear nights, unusually bright for its color but far dimmer than any of the visible planets. It never rivals the brilliance of Earth’s Mars or Jupiter but stands out by hue alone. Under ideal conditions it can even cast the slightest hint of red-shifted illumination on reflective surfaces, though this is subtle and easily missed.
Galen Beta is not a placid ember. Its rotation is slow enough that it is not in the continuously furious category of flare stars, yet fast enough to sustain a vigorous magnetic engine. Observatories detect a steady hum of X-ray flicker and a profusion of starspots that slowly march across the face of the star as it turns. The heavens over a Beta planet are often alive with sudden red-white flares and green auroral curtains that leap when a particle storm hits.
Its slow-motion orbit ensures that its position in Galentor’s sky changes only over geological timescales. To the inhabitants, Beta is a constant ember burning on the edge of the night.
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