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In My 2300 Universe Discussion of non-canon ideas for use in your 2300 Universe

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Old October 13th, 2008, 02:47 AM
rfmcdpei rfmcdpei is offline
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Default A Survey of Gamma Pavonis

The below system outline and history comes from some postings I made at the 2300noncanon list. It was an interesting exercise in creating a backwater planetary system with a marginal garden world. My thanks to the commenters who helped me flesh out the system.

* * *

1. System History

The Gamma Pavonis system coalesced an estimated 9 100 thousand million years ago, centered around its sun. With a mass eight-tenths that of Sol, a spectral classification of F7 V (on the main sequence of stellar evolution), and a luminosity one-half greater than that of Sol, the physical characteristics of Gamma Pavonis at first appears to be an anomaly, with a luminosity much greater than its mass would seem indicate. However, like Beta Hydri and 82 Eridani, Gamma Pavonis is an old disk star, formed early in the galaxy's history at a time when elements heavier than helium were relatively rare. Gamma Pavonis' low stellar metallicity ensured that the star would consume its hydrogen fuel more quickly and hence more intensely than stars of comparable mass (for example, Tau Ceti). Gamma Pavonis' stellar metallicity, only one-fifth that of Sol, has ensured that the star will experience a considerably shorter lifespan than other, metal-rich, stars its mass; it is expected to go off the main sequence of stellar evolution and become a red giant somewhat like Arcturus in the French Arm.

One consequence of Gamma Pavonis' low metallicity was the failure of Gamma Pavonis' protoplanetary disk to coalesce into more than six planets. Gamma Pavonis I, a world roughly one-quarter larger than Earth but with a density 20% lower, formed close to Gamma Pavonis, in a circular orbit just 0.3 astronomical units away from its primary. At an early stage in the system's history, Gamma Pavonis I was tidally locked with its primary, so one hemisphere permanently faced the star while another hemisphere permanently faced away. Gamma Pavonis IV and V, located in the outer Gamma Pavonis planetary system, quickly evolved into ice giants like Uranus and Neptune in Sol system, while Gamma Pavonis II (separated from Gamma Pavonis I by a sparse asteroid belt) evolved into small planetoid similar to Ceres. None of these worlds had moons of significant size, although Gamma Pavonis IV and V did capture asteroidal and cometary objects within their gravity wells. The nascent planetary system experienced a period of heavy bombardment by cometary and asteroidal objects between 8 300 and 7 900 million years ago, but following this period of heavy bombardment little evolved in most of the planetary system.

Events at Gamma Pavonis III and IV, however, proved more eventful. Manchurian and Japanese studies suggest that unlike the Earth-Moon binary planetary system, where the Moon formed as a result of a Mars-size protoplanetary object's collision with Earth, Gamma Pavonis III and IV formed quiescently enough in the same orbit, each condensing into planetary bodies roughly 8 800 million years ago. Sharing a common orbit 1.69 AU from their primary, with a year of 2.456 Earth years and an orbital eccentricity of 0.02, the two worlds quickly became tidally locked: At its closest, Gamma Pavonis IV was barely 50 thousand kilometres away from the heavier Gamma Pavonis III.

Gamma Pavonis III is 10% denser than Earth, masses 0.15 Earths, is 6600 kilometres in diameter, has a surface gravity of 0.56 Earth, and possesses an escape velocity 54% of Earth's. With an axial tilt of 2 degrees, anchored by the presence of nearby Gamma Pavonis IV, seasonal variation is marginal. III's day is 32h14minutes long, the same as IV's orbital period; one hemisphere of III, the sublunar, always faces IV. Gamma Pavonis IV is smaller and lighter, with only 2.7% of Earth's mass, a surface gravity of 0.274 g, a density of 0.9 Earth, and diameter of 4017 kilometres, orbiting 59 400 kilometers away from II. II and III are shadowed two by two asteroidal bodies, one a carbonaceous chrondite, one a dense nickel-iron body, one located in the Lagrange point ahead of III/IV and the other behind the binary planet.

II. Gamma Pavonis III History

Within the first thousand million years of Gamma Pavonis III's existence, life developed. Japanese drillings on their Northern Continent base suggest that life on Gamma Pavonis III evolved much like life on Earth, with unicellular organisms developing first, eventually colonizing the oceans. Unfortunately for Gamma Pavonis II's biosphere, its homeworld's extreme distance from the considerably dimmer young Gamma Pavonis contributed to the onset of a deep and irreversible planetary ice age no later than 7 700 thousand million years ago. As the planet's surface froze, life retreated to the oceans; as the oceans began freezing, life retreated to geological hot spots on the ocean floor, to volcanic vents, and deeper into the planet's crust.

The low mass of Gamma Pavonis III, worse, contributed to the world's rapid cooling, so that many of the oceanic hot spots began to freeze beginning some 4 000 million years ago as the planet became geologically dead. The failure of scientific exploration to reveal preserved traces of life between 4 000 million and 300 million years ago reflects life's extreme scarcity on Gamma Pavonis III for most of the world's history, trapped in scattered marginal ecologies. Infall of simple organic compounds onto the world's ice-covered surface produced some brief and localized heating, but in general the world remained cold and barren.

300 million years ago, as Gamma Pavonis' energy output grew, Gamma Pavonis III and IV were brought within the system's life zone (the outer boundary of the life zone now lies 1.71 astronomical units from Gamma Pavonis). As the world began to warm and the oceans melt, life began to emerge into a more hospitable environment. As the world's ice melted, it released the organics fallen onto the world's surface over the previous thousands of millions of years, introducing the starved organisms to a bonanza of easily-digestible nutrients. Speciation appears to have proceeded quite rapidly, as the remnant unicellular species from Gamma Pavonis III's early history began to occupy new niches as soon as they became available. The high radiation influx from Gamma Pavonis, rich in ultraviolet light, acted to encourage mutation and speciation. At present, despite its thin carbon dioxide-dominated atmosphere and low temperatures, Gamma Pavonis III is more hospitable to life than at any point since the onset of its ice age.

Unfortunately, life on Gamma Pavonis III is doomed. The star Gamma Pavonis is expected to leave the main sequence and become a red giant star within the next 200 million years, increasing vastly in luminosity and size, consuming Gamma Pavonis I. Long before this, though, the increasing luminosity of Gamma Pavonis will cause the runaway greenhouse heating of Gamma Pavonis III, eventually boiling off all of the world's volatiles into space and exterminating all life.

Last edited by rfmcdpei; October 13th, 2008 at 02:51 AM.. Reason: typos
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