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. 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.

## 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.
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.