Chiron

Chiron, also called Planet, is the setting of Alpha Centauri and its expansion.

Overview
Planet is about 20% larger than Earth, with an equatorial diameter of 9,370 miles. Planet's larger heavymetal core gives it an average density 11% higher than Earth's. The result is significantly higher surface gravity, 30% greater than that of Earth. The colonists suffered a variety of effects due to this higher gravity. Planet is a bit farther from Alpha Centauri A than Earth is from the Sun, but Alpha Centauri A is brighter than the Sun, and these differences offset, so that Alpha Centauri A is almost exactly as bright from Planet as the Sun is from Earth.

One Planet year is 532 local days long. Since there is no significant seasonal cycle, the colonists rarely used the local year as a measure of time. Instead, they used the "Mission Year," which was equal in length to the Earth year, and used the same system of reckoning. Thus, the Unity arrived in the Alpha Centauri system in Mission Year 2100. One Mission Year was just over 500 local days long; the colonists added one or two local days to each Mission Year as needed, to keep in sync with the Earth year. However, Planet’s days are also only about 18 hours, so sleep cycles must be correspondingly reduced. Its years are slightly longer than Earth’s years., but not enough to make a noticeable difference. The greater difference is Planet’s lack of seasons. With only a slight axial tilt, any seasonal differences are minimal. Neither of Planet’s moons exert as much tidal pull as Earth’s moon, but when they combine, tides will run slightly higher than on Earth. Once every 80 years, as Alpha Centauri B reaches perihelion (its closest approach to Alpha Centauri A), it generates enough heat to increase Planet’s average temperature by 0.3° C. That doesn’t seem like much, but Planet’s climactic system might easily amplify this to uncomfortable levels. In fact, any life native to Planet may have evolved cyclic responses to this event.

The atmosphere consists of 90.9% Nitrogen, 8.5% Oxygen and .01% Carbon Dioxide. The low oxygen content results in fewer forest fires, a higher proportion of anoxic (oxygen-free) environments — encouraging a large anaerobic ecosystem reducing nitrates to break down organic matter — and a plant ecosystem dominated by the need to conserve carbon.

Meteorology and climatology
Planet’s larger size and gravity result in a significantly higher sea level pressure than Earth’s: 1.74 atmospheres (that is, 74% greater air pressure at sea level than on Earth). This brings the partial pressure of Oxygen (15k Pascals) up to acceptable levels, but the high overall pressure combined with such a large quantity of Nitrogen produces deadly Nitrogen narcosis in unprotected humans. Human colonists would have to wear pressure helmets, at the very least. The temperature bands running along the surface of Planet are the most obvious climactic pattern. As on Earth, solar energy warms the equatorial areas, and the weather cools as you migrate towards the poles. Thus, equatorial regions produce more energy, while the poles tend to have more mineral resources.

The rainfall patterns of Planet depend on the wind currents, which always blow from west to east. Since the wind carries moisture with it from the oceans, rain tends to fall on the west side of mountain ranges. You can see this trend when looking at a big continent — green predominates on the western coast, indicating a great deal of rainy or moist terrain, while the east coast remains dry and barren. Rainfall determines the amount of nutrients that may be collected, so often the west coast of a continent proves a better source of nutrients than the east coast. On flat continents or small islands, no elevations exist to trap the rainfall, and so moisture tends to be more evenly distributed. Also, river valleys usually have a reasonable amount of rain, so a river running through a dry area can be a good base location.

The warm tropical seas of Planet are breeding grounds for hurricanes, which are also encouraged by the high gravity and rapid rotation. The dense nitro- gen atmosphere only partly offsets this. The equatorial cloud belts, however, help to regulate the climate by reflecting sunlight.

At over 20% higher insolation than Earth, Planet has very small polar ice caps. The effect of this on the oceanic circulation is profound. Instead of cold oxygen-rich polar water sinking at the poles and being carried in a current along the ocean floor to the equator (as on Earth today), the circulation is driven in reverse, with warm saline oxygen-poor water sinking at the equator and flowing to the poles. As a result, the bottom waters have little oxygen.

Soil composition
Compared to Earth, silicates are much less common in the soils of Planet. As in the tropics on Earth, warm water leaches the silica from clays, leaving a poor alumina-rich soil. (This does not prevent rain forests from growing, but will inhibit agriculture.) The arctic regions have a higher proportion of acidic soils with a high proportion of organic matter (podzols) which is equally hard to farm. The temperate soil zone, which on Earth is favoured with rich alumi- nosilicate clays, is much narrower on Planet, and the soils are more likely to be sandy or lime-rich. Bogs are also common.

Ecology
Although basically similar to Earth life, in that it is based on carbon compounds in water, the organisms of Planet have evolved a biochemistry very different from Earth. The scarcity of carbon in the environment, and of dioxygen in the soil, has forced plants to try to make do without O2 (oxygen), and to economize on the use of carbon in structural parts and as an energy storage material. They do this by using a biochemical reaction unknown on Earth. Planet’s plants seem to have a special enzyme to encourage this reaction, possibly with the aid of sunlight. They use the nitrate obtained this way to store energy as organic nitro-compounds, to reduce carbonates to carbon, and to carry out respiration in anoxic environments.

The prevalence of anoxic (oxygen-free) environments rich in organic material, combined with the presence everywhere on Planet of nitrated compounds, has led to an astonishing variety of underground organisms which live in the absence of oxygen (though they can use oxygen if it is present) and “breathe” nitrate. This ecosystem apparently has symbiotic relations with the plants and with Planet’s animal life. Also note that the prevalence of nitrate in the environment has serious repercussions.

Nitrous oxide is present in only small amounts as it combines with ozone in the stratosphere to break down into N2 and O2 (which prevents the build-up of an ozone layer). When plant material is buried, nitro-hydrocarbons have all they need to “burn,” so they do so slowly underground, leaving nothing behind until all the reducing material (hydrocarbon) or all the oxidizing material (nitrate) has gone. Nitrate nearly always runs out first, leaving a residue of carbon compounds. Provided this does not come into contact with oxygen, it fossilizes to produce ordinary fossil fuels. Since Planet has been hot and hypoxic for a long time, it should be expected to have all the oil, shale and coal anyone could want, depending on the efficiency of the ecosystem. Regardless of any attempt to wipe out the underground nitrate respirers, all efforts to return carbon to the biosphere would encourage Planet life to proliferate.

Conversely, the huge quantities of nitrate in the soil would be heaven to human farmers. However, water would have to be treated in order to remove the nitrates so that it is safe to drink; otherwise humans would suffer from methhemoglobinemia, or “blue baby syndrome,” where the red blood cells are poisoned so they can’t take up oxygen. The best way to treat this water is to pass ozone through it to destroy the nitrate.

Landmarks

 * See Landmarks

Astrophysics
The brightest member of the Alpha Centauri system is Alpha Centauri A, simply called "the sun" by the colonists. It is of the same spectral class as Sol and emits the same comfortable yellow white light. It is somewhat more massive than Sol and significantly brighter.

Alpha Centauri B was named Hercules by the colonists, after the Greek hero who was a great nemesis of the mythical Centaur race. Hercules is a smaller, cooler star, with light more orange in color than that of its partner. Alpha Centauri A and B orbit around their mutual center of mass, somewhere in the space between. Every 80 Earth years, Hercules comes within 11.4 AU of the sun, or somewhat more than the average distance between Sol and Saturn. At their most distant, the two stars are about 35.8 AU apart, or a little less than the average distance between Sol and Pluto.

An observer on Chiron will always see Hercules as the brightest of the "fixed" stars, between 140 and 1,400 times as bright as a full moon on Earth. Even at its most distant, Hercules is more than bright enough to read by at night. At its closest, it has a small but measurable effect on Chiron's climate. The 80-year cycle of Hercules' close approaches gives rise to "grand seasons" on Chiron, affecting the growth and behavior of native life forms.

Alpha Centauri C is much smaller than its two partners. It is a red dwarf star, only a small fraction of Sol's mass and less than one tenthousandth as bright. It is remarkable primarily for its very low mass, and for its nature as a highly active flare star. From hour to hour, Alpha Centauri C experiences constant stellar flares, any one of which may as much as double its normal brightness.

Alpha Centauri C was once called Proxima Centauri, since it is significantly closer to Earth than the A-B

pair. In fact, for many years it was suspected to be an independent wanderer, close to the A-B pair out of sheer happenstance. The Unity expedition was the first to prove otherwise. As it turns out, Proxima does orbit the A-B pair, but at a tremendous distance. It never approaches more closely than 0.25 ly, and takes over half a million Earth years to complete one cycle. From Chiron, Alpha Centauri C is a dim star lost among the galaxy's millions, only visible to the naked eye if the observer knows precisely where to look. As such, it was never given a mythological name of its own, and was called simply "C" or "Proxima" by the colonists.

Other bodies
The presence of Hercules in the Alpha Centauri system is ironically appropriate. Its mythical namesake killed a number of Centaurs during his career. The star Hercules is probably responsible for destabilizing the orbits of several planets which once circled Alpha Centauri A.

As it stands, Alpha Centauri A has only one planet other than Chiron. The planet Eurytion orbits A at a distance of 0.47 AU, somewhat greater than the average distance between Sol and Mercury. Eurytion is quite similar to Mercury in many respects, about half again as massive and slightly denser. Due to the long-term effects of solar tides, Eurytion does not rotate with respect to Alpha Centauri A. Its "day face" is fiercely hot, with temperatures high enough to melt lead in places. On the other hand, the planet's "night face" is bitterly cold, with temperatures falling very close to absolute zero at the point furthest from the sun.

Eurytion is a treasure world, dense and rich in heavy metals, with traces of frozen water and other volatile compounds on its night face. Late in the history of the Chiron colony, the various human factions established outposts there.

Aside from Eurytion and Chiron, there are no planets of significant size circling Alpha Centauri A. Beyond Chiron's orbit there is a broad scatter of asteroids, many of which trace complex paths perturbed by the gravitational pull of Hercules. Hercules and Proxima have planets of their own, but these played almost no part in the history of humanity on Chiron.

Moons
Chiron has two moons, named Nessus and Pholus. Pholus is the inner moon, with about 1/5 the diameter and 1% the mass of Earth ' s moon. Its orbit is almost a perfect circle, with a radius of about 60,000 miles. Its synodic month (the period from one full moon to the next) is 3.7 local days, and there are 144 such months in the course of Chiron's year. Pholus is a battered-looking moon, gray and cratered, which moves visibly against the background stars.

Nessus, the outer moon, has about 1/2 the diameter and 9% the mass of Earth's moon. Its orbit is also nearly circular, with a radius of about 124,000 miles. Its synodic month is 10.6 local days, and there are 50 such months in a local year. Nessus is relatively bright, with several large craters associated with "rays" of reflective dust.

The orbits of Nessus and Pholus fall in the same plane, and the orbital radius of Nessus is almost exactly twice that of Pholus. As a result, the two moons appear to be roughly the same size from the surface of Chiron, each a little smaller than the Moon once appeared in Earth's sky. Each moon partially eclipses Alpha Centauri A from time to time (they are too small to cover the sun's disk entirely). Far more frequent are lunar eclipses, in which one or the other moon moves through Chiron's shadow. Even more frequent are the occasions on which Pholus passes in front of Nessus from the point of view of observers on Chiron.