This is a write up of Pentaurus, a planet in 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.
Pentaurus, Galen Alpha b
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| Pentarus, first planet in orbit around Galen Alpha (the Athyric Rift is clearly visible in this photo) |
Mass : 0.55 x Earth
Diameter: 10,242 kilometres
Density: 5.84 grams per cubic centimetre
Average temperature: 99.1 degrees Celsius (372 Kelvin) (minimum 1.64 degrees Celsius, maximum 123 degrees Celsius)
Rotational Period: 0.321 days
Orbital Period: 97.6 days
Surface gravity : 0.852 g
Semi-Major Axis of orbit : 0.42 AU
Eccentricity of orbit : 0.0139
Inclination of orbit: 1.10 degrees
Obliquity : 13.8 degrees
Pentaurus is the innermost planet of the Galen Alpha system, a scorched but enduring rocky world whose surface tells a story of lost oceans, planetary stress, and long, slow desiccation. Seen from orbit, Pentaurus presents a striking ochre and rust coloured globe, scarred by vast tectonic ruptures and mineral plains that glow faintly under the light of its parent star.
Appearance from Orbit
From space, Pentaurus is immediately recognisable by a colossal, planet spanning fracture zone that arcs across much of the visible hemisphere. This immense scar, kilometres deep in places, is believed to be the remnant of early global tectonic failure, possibly triggered by rapid internal cooling combined with tidal stresses during the system’s formative era. The fracture is not a single canyon, but a complex network of collapsed crust, rift valleys, and exposed mantle rock.
Surrounding this great rift are wide expanses of smoother terrain, coloured pale tan to deep ochre. These regions are interpreted as ancient seabeds and evaporite plains, where long vanished oceans once deposited thick layers of salts and fine sediments before retreating completely.
Scattered darker regions mark areas of denser basaltic crust or volcanic resurfacing, while lighter patches are consistent with salt flats and mineral precipitates, highly reflective and chemically altered by long exposure to stellar radiation.
Geological Character
Pentaurus is a dense, metal rich terrestrial planet, and its surface reflects a world that has endured enormous internal stress. Although large-scale volcanism has long since declined, geothermal activity remains present in isolated regions, particularly along tectonic boundaries and within deep canyon systems. Here, heat from the mantle still finds pathways to the surface, creating fumaroles, mineral vents, and occasional thermal outbursts.
The great fracture system visible from orbit still experiences minor seismic activity. These slow crustal movements periodically expose fresh rock faces and release trapped gases, contributing to the thin, chemically harsh atmosphere.
Climate and Environment
Pentaurus is hot, dry, and unforgiving. Its proximity to Galen Alpha results in strong solar heating, while its rapid rotation prevents extreme temperature locking between hemispheres. The planet experiences short, intense days and nights, producing strong thermal winds that carry fine mineral dust across the surface.
There is no stable surface water. However, mineral salts and hydrated compounds remain widespread, offering clear evidence of a wetter past. In low lying basins, transient brine films may briefly form under favourable conditions, evaporating quickly and leaving behind fresh crystalline deposits.
The atmosphere is thin and dominated by heavy gases, incapable of sustaining complex life on the surface. Nevertheless, the planet remains of great interest to scientists, as its crust preserves a remarkably clear record of planetary desiccation.
The Athyric Rift (also known as the Athyric Chasm Complex)
The vast canyon network visible across much of Pentaurus’s surface is known collectively as the Athyric Rift. Spanning nearly a quarter of the planet’s circumference, it is one of the largest continuous tectonic fracture systems known in the Galen Alpha system.
Origin and Formation
The Athyric Rift is believed to have formed during Pentaurus’s early cooling phase, when the planet’s dense metallic core contracted faster than its brittle outer crust. This contraction, combined with tidal stresses from Galen Alpha and the formative impact that created Calyx, caused the lithosphere to fail catastrophically along a global fault line.
Rather than forming a single canyon, the failure propagated laterally, producing a braided system of chasms, collapsed plateaus, and exposed mantle shelves. Some sections exceed 12 kilometres in depth, with stepped walls revealing clearly stratified mineral layers from Pentaurus’s oceanic era.
Physical Characteristics
The rift varies dramatically along its length:
- Primary chasm zones form sheer walled trenches hundreds of kilometres wide.
- Fracture fields consist of shattered crust, tilted slabs, and collapsed basins.
- Salt exposed terraces line many interior walls, glowing pale white or pink in orbital imagery.
- Dark thermal scars mark regions where mantle heat still rises close to the surface.
- In several locations, the canyon floor drops below what would once have been Pentaurus’s global sea level, strongly supporting the theory that ancient oceans drained into the Athyric Rift during the planet’s final desiccation phase.
Geothermal Activity
The Athyric Rift remains the most geologically active region on Pentaurus.
Isolated geothermal vents, mineral geysers, and superheated fumaroles dot the canyon floor and lower walls. These vents release sulphur compounds, metal vapours, and trace gases, creating shimmering heat plumes visible from orbit during favourable lighting.
Several of these regions are considered potential refugia for extremophile microbial life, sheltered from radiation and temperature extremes within mineral rich caverns.
Scientific and Exploratory Significance
For offworld researchers, the Athyric Rift is often described as a planetary autopsy laid bare. Its exposed layers provide a continuous geological record spanning more than two billion years. Ancient evaporite deposits preserve chemical signatures of Pentaurus’s lost oceans.
Seismic sensors placed along the rift detect slow, rhythmic crustal adjustments, suggesting the planet is still settling into long term equilibrium. The Rift’s complexity also makes it notoriously dangerous. Sudden rockfalls, ground collapse, and unpredictable thermal releases have claimed several AI probes.
Cultural and Narrative Notes
Among early Galen explorers, the Athyric Rift earned a grim reputation. Survey crews referred to it as “the planet’s open wound”, a phrase that later entered common astrogeological literature.
In some speculative xenohistorical theories, the Rift is believed to have influenced early life evolution on Pentaurus, acting as a final refuge zone as surface conditions deteriorated.
Secondary and Colloquial Names
Different traditions and organisations use alternate names for parts of the system:
The Worldscar – used by early deep space navigators.
The Ochre Divide – a poetic name referencing its colour contrast.
The Saltfall Trenches – used for regions rich in exposed evaporites.
The Calyx Line – a nickname among astronomers linking the rift’s origin to the moon forming impact.
A World of Narrative Significance
Pentaurus is not a dead world but a quietly active one. Its immense rift systems, salt deserts, and geothermal pockets make it an ideal setting for lost research stations, hidden subterranean installations, or ancient experiments abandoned when the planet’s habitability collapsed.
In the context of the Galen system, Pentaurus serves as a cautionary counterpoint to Galentor. Where Galentor flourished, Pentaurus endured. Its surface stands as a planetary fossil, preserving the moment when a world slipped just too close to its star and paid the price.
For travellers, Pentaurus is a place of stark beauty and deep time, a planet that invites exploration not for what lives there now, but for what once did, and what secrets still lie buried beneath its fractured crust.
Calyx
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| Calyx, the moon of Pentaurus |
Mass : 0.0066 x Earth ( 0.536 x Moon )
Diameter: 3,318 kilometres
Density: 2.06 grams per cubic centimetre
Average temperature: 164 degrees Celsius (437 Kelvin) (minimum 136 degrees Celsius, maximum 167 degrees Celsius)
Rotational Period: 5.88 days
Orbital Period: 2.68 days
Surface gravity : 0.0975 g
Semi-Major Axis of orbit : 60,318 kilometres
Eccentricity of orbit : 0.0139
Inclination of orbit: 1.10 degrees
Obliquity : 151 degrees
Pentaurus is orbited by a single natural satellite, Calyx, a small but geologically distinctive moon that plays a subtle role in the planet’s long-term evolution.
Calyx is thought to have formed from debris generated by a major early impact on Pentaurus, an event that likely contributed to both the planet’s rapid loss of volatiles and the initiation of large-scale crustal fracturing that culminated in the Athyric Rift. Its composition supports this origin: Calyx is relatively low in density, with a mixed silicate and volatile-poor mantle, suggesting it accreted from already differentiated planetary material rather than forming independently.
The moon orbits unusually close to Pentaurus, completing a revolution in less than three days. Despite this proximity, its orbit is remarkably regular, with only a slight eccentricity and a low inclination relative to Pentaurus’s equatorial plane. Tidal interactions have long since locked Calyx into synchronous rotation, though its axial orientation is extreme. With an obliquity exceeding 150 degrees, Calyx effectively rotates in a retrograde, upside-down configuration, likely the lasting consequence of chaotic angular momentum transfer during its formation.
Calyx is intensely heated. Its surface temperatures are high even by inner-system standards, driven primarily by tidal stress and residual radiogenic heat rather than direct stellar illumination alone. While it lacks the violent volcanism seen on moons like Tarack elsewhere in the Galen system, Calyx exhibits widespread crustal deformation, extensive fracture fields, and regions of softened, partially molten rock beneath a brittle outer shell. Localised lava effusions and sulphur-rich deposits have been detected along major fault zones, particularly on the hemisphere facing Pentaurus.
The surface itself is pale, scorched, and uneven, marked by smooth plains of reworked impact material interspersed with uplifted ridges and collapsed basins. Few large craters remain intact, as surface renewal processes have erased much of the moon’s early bombardment record.
From Pentaurus’s surface, Calyx appears large and unsettlingly close, moving rapidly across the sky. Its pale, heat-blanched face reflects sunlight weakly, but during certain alignments it can be seen glowing faintly in the infrared, a visible reminder of the immense energies still at work within the inner Galen Alpha system.
Though Calyx is far too hostile to support life, it remains a world of great scientific interest. Its interior retains a thermal memory of Pentaurus’s violent youth, and continued study of the moon has yielded valuable insight into early planetary differentiation, tidal evolution, and the destabilising effects of close-orbit satellites in young stellar systems.
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| Calyx's orbit around Pentaurus |
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