Archive for August, 1998


From: Daniel Boese <>
Subject: Sid Meier's Alpha Centauri
Date: 1998/08/04
Message-ID: <6q7k7h$31f$>
X-Deja-AN: 377902017
Organization: Niagara's Electronic Village
User-Agent: tin/pre-1.4-980226 (UNIX) (IRIX/5.3 (IP22))

(I posted this last Thursday, but my local server lost its newsfeed for a
while. If this shows up twice, my apologies.

 As I'm sure a number of you know, a new science-fiction game is coming
out this fall. "Sid Meier's Alpha Centauri - A Brian Reynolds Design" is a
turn-based strategy game detailing the future history of a colonization
mission to Alpha Centauri, which has an accident along the way; the crew
breaks up into competing factions.

 Brian Reynolds has posted some detailed data about this fictional Alpha
Centauri planetary system to the forums at However,
as they're buried among thousands of other messages, I've collected the
pertinent data, and am posting it here to promote interest in the game and
discussion about the specifics.


   The planet will mostly be referred to in the game as "Planet",
   although its astronomical name is Chiron. Its two moons are Nessus and
   Pholus. For reasons involving stability of orbits in binary systems,
   there is only one other planet, Eurytion, which is more or less like
   Mercury. Alpha Centauri B (the K-class twin star) has one Jovian

   Atmosphere has a much higher Nitrogen (N2) partial pressure than Earth
   (2.02 ratio), w/ Oxygen .71 compared to Earth, CO2 .67 ratio, argon
   1.06 ratio and total air pressure 1.74 atmospheres. So it's fine for
   earth plants (and the abundant nitrates in the soil help a great
   deal), but nitrogen narcosis problems prevent direct breathability by
   The much higher nitrogen partial pressure (and resulting lower oxygen
   partial pressure) will tend to make things like forest fires
   considerably less likely.



   Solar                constants   Sun       Alpha A   Ratio
   Mass                 kg          1.99E+30  2.15E+30  1.08
   Luminosity           W           3.89E+26  5.63E+26  1.45
   Radius               m           6.96E+08  7.59E+08  1.09

   Planetary           constants    Earth     Planet/   Ratio

   Mass                 kg          5.98E+24  1.10E+25  1.84
   Equat. radius        m           6.38E+06  7.54E+06  1.18
   Dist. from star      m           1.50E+11  1.60E+11  1.07
   Axial tilt           degrees     23.45     2.00      0.09
   Surface area         m^2         5.10E+14  7.18E+14  1.41
   Standard gravity     m/(s^2)     9.81      12.85     1.31
   Escape velocity      m/s         11184     13947     1.25
   Density              kg/(m^3)    5519      6150      1.11
   Size of sun          degrees     0.27      0.27      1.02
   Year                 our days    365.3     388.6     1.06
   Year                 local days  365.3     532.0     1.46
   Day                  hours       24.00     17.53     0.73
   Mountain height      m           10626     8112      0.76
   Horizon distance     m           5051      5493      1.09
   Ocean tide (sun)     m           0.12      0.12      0.94
   Ocean tide (moon 1)  m           0.27      0.18      0.67
   Ocean tide (moon 2)  m                     0.11
   Ocean tide (both)    m           0.39      0.41      1.05
   Orbital Circumfrnce  m           9.42E+11  1.01E+12  1.07
   Orbital Speed        m/s         29861     29942     1.00


   Total pressure       Pa          101325    176020    1.74
   Nitrogen             Pa          79125     >160000   2.02
   Oxygen               Pa          21228     <15000    0.71
   Argon                Pa          942       1000      1.06
   Carbon dioxide       Pa          30        <20       0.67

   Nitrogen                         78.09%    90.90%    1.16
   Oxygen                           20.95%    8.52%     0.41
   Argon                            0.93%     0.57%     0.61
   Carbon dioxide                   0.03%     0.01%     0.4

   Surface density      kg/(m^3)    1.22      2.06      1.68
   "Flammability"       mmol K J-1  7.17      2.87      0.40

   Effective temp.      K           253       261       1.03
   Greenhouse effect    K           +36       +32       0.90
   Surface temp.        K           288       293       1.01
   Surface temp.        C           15.4      19.7      1.28
   Solar constant       W/(m^2)     1383      1750      1.27

   Moon #1 (Nessus)                 The Moon  Nessus    Ratio

   Mass                 kg          7.35E+22  6.50E+21  0.09
   Radius               m           1.74E+06  8.00E+05  0.46
   Dist. from planet    m           3.84E+08  2.00E+08  0.52
   Surface area         m^2         3.80E+13  8.04E+12  0.21
   Mean gravity         m/(s^2)     1.62      0.68      0.42
   Density              kg/(m^3)    3342      3031      0.91
   Synodic month        our days    29.5      7.7       0.26
   Synodic month        local days  29.5      10.6      0.36
   Syn. months/yr                   12.4      50.2      4.05
   Angular radius       degrees     0.26      0.23      0.88

   Moon #2 (Pholus)                 The Moon  Pholus    Ratio

   Mass                 kg          7.35E+22  5.20E+20  0.01
   Radius               m           1.74E+06  3.50E+05  0.20
   Dist. from planet    m           3.84E+08  1.00E+08  0.26
   Surface area         m^2         3.80E+13  1.54E+12  0.04
   Mean gravity         m/(s^2)     1.62      0.28      0.17
   Density              kg/(m^3)    3342      2895      0.87
   Synodic month        our days    29.5      2.7       0.09
   Synodic month        local days  29.5      3.7       0.13
   Syn. months/yr                   12.39     143.76    11.60
   Angular radius       degrees     0.26      0.20      0.77

   Eurytion (Mercurian planet)      Earth     Eurytion  Ratio

   Mass                 kg          5.98E+24  5.16E+23  0.09
   Equat. radius        m           6.38E+06  2.82E+06  0.44
   Dist. from star      m           1.50E+11  7.06E+10  0.47
   Surface area         m^2         5.10E+14  9.98E+13  0.20
   Standard gravity     m/(s^2)     9.81      4.33      0.44
   Escape velocity      m/s         11184     4942      0.44
   Density              kg/(m^3)    5519      5503      1.00
   Size of sun          degrees     0.27      0.62      2.31
   Year                 our days    365.3     113.8     0.31
   Year                 local days  365.3     SYNCHRONOUS
   Horizon distance     m           5051      3357      0.66
   Surf. temperature    K           288       438       1.52
   Surf. temperature    C           15.4      165.3     10.71
   Solar constant       W/(m^2)     1383      8999      6.51


   Preliminary report on the Chironian biosphere

   Introduction - the astrophysical background

   Alpha Centauri A ("Alpha Prime") is a G2V main sequence star, similar
   in spectral class to the Sun, but about a billion years older. Chiron
   (or "Planet" as most of the colonists refer to it) is a 1.8 Earth mass
   planet orbiting at 1.08 AU from Alpha Prime, receiving 23% more
   sunlight than Earth does at the present.

   Like the Sun, Alpha Prime was once about 30%-40% dimmer than its
   present luminosity. Stars grow continually more luminous over their
   lifetime on the main sequence - this was a matter of some concern to
   astronomers in the past (Hart 1978) who reasoned that if the Sun had
   been much less luminous than it is today, then the Earth should have
   been locked in a permanent ice age. But the geological record shows
   that Earth was not significantly cooler than it is today. This was
   known as the Faint Young Sun Paradox.

   It was Walker and Kasting who pointed out (1981) that if the Earth had
   had a much greater amount of CO2 in the atmosphere, then the CO2
   greenhouse effect could account for the difference. CO2 is emitted
   into the atmosphere from volcanoes and weathered out of the atmosphere
   by the reaction

   CaSiO3 + CO2 ---> CaCO3 + SiO2
   calcium  carbon   lime    silica
   silicate dioxide

   The carbonate rocks are eventually subducted into the mantle by
   continental drift, broken down into silicate rocks and CO2, and the
   cycle begins again. The crucial feature of this cycle is that the
   weathering reaction is temperature dependent: the higher the
   temperature, the faster CO2 is removed from the atmosphere. So the
   carbonate-silicate cycle acts as a planetary thermostat, keeping
   temperatures constant even while stars vary over geological time.

   On Earth, the consequence was that life evolved in an atmosphere of up
   to 1000 millibars CO2 or even more. The first photosynthesising
   organisms using atmospheric CO2 may have evolved up to four billion
   years ago and have dominated the biosphere ever since. But on Chiron,
   the temperature was already too high to support a dense CO2
   atmosphere, and carbon was a much less available element in the warm
   early seas. This has led to a very different evolutionary path.

   Chiron today - atmospheric composition

   The atmosphere consists of >160 kPa N2, <15 kPa O2 and <20 Pa CO2. The
   low oxygen content results in fewer forest fires, a higher proportion
   of anoxic environments - encouraging a large anaerobic ecosystem
   reducing nitrates to break down organic matter, about which more later
   (see report on "xenofungus") - and a plant ecosystem dominated by the
   need to conserve carbon.

   Meteorology and Climatology

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

   Because the planet spins faster, the winds follow the lines of
   latitude more strictly than on Earth. Moreover, the meridional
   circulation splits into five cells, as opposed to Earth's three
   (Hadley, Ferrel, and Rossby). Compare this to the bands on a giant,
   rapidly rotating planet like Jupiter or Saturn.


   At over 20% higher insolation than Earth, Chiron 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
   on Earth in the Cretaceous period). As a result, the bottom waters are
   highly anoxic (note: such seas are called euxinic after the Black

   Soil Composition

   Compared to Earth, silicates are much less common in the soils of
   Chiron. 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
   aluminosilicate clays, is much narrower here on Chiron, and the soils
   are more likely to be sandy or lime-rich. Bogs are also common.


   Although basically similar to Earth life, in that it is based on
   carbon compounds in water, the organisms of Chiron have evolved a
   biochemistry very different Earth. The scarcity of carbon in the
   environment, and of dioxygen in the soil, has forced plants to try to
   make do without O2, and 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

   N2 + H2O + 5/2O2 --> 2H+ + 2NO3- ( -7 kcal mol-1 )

   as can be seen, this reaction is exothermic, but (thankfully) is
   unknown on Earth. Chironian 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 (see report on "gun-cotton trees"); to reduce
   carbonates to carbon; and to carry out respiration in anoxic

   The prevalence of anoxic environments rich in organic material,
   combined with the presence everywhere on Chiron of nitrated compounds
   has led to an astonishing variety of underground organisms (see report
   on "xenofungus") which live in the absence of oxygen (though they can
   use oxygen if it is present) and "breathe" nitrate:

   (CH2O) + NO3 ---> H2O + CO2 + 1/2N2O + 1/4O2

   This ecosystem apparently has symbiotic relations with the plants and
   with Chironian animal life (see report on "mind worms"). The
   prevalence of nitrate in the environment has serious repercussions
   (see below).

   The nitrous oxide is present in only small amounts as it combines with
   ozone in the stratosphere to break down into N2 and O2

   N2O + O3 ---> 2NO + O2 ; 2NO ---> N2 + O2

   This process prevents the build-up of an ozone layer.

   Fossil Fuels

   When plant material is buried, nitro-hydrocarbons have all they need
   to "burn", so they will do so slowly underground, leaving nothing
   behind until all the reducing material (hydrocarbon) or all the
   oxidizing material (nitrate) has gone. We expect the nitrate to run
   out first in all cases, leaving a residue of carbon compounds.
   Provided this does not come into contact with oxygen, it will
   fossilize to produce ordinary fossil fuels. Since Chiron has been hot
   and hypoxic for a long time, it should have all the oil, shale, and
   coal the colonists could want.

   This will be a focus of the colonists' terraforming efforts to
   increase the CO2 (and hence oxygen) as they transplant Earth
   vegetation to Chiron. They will also want to blast chalk limestone
   deposits (which are also abundant on Chiron) to liberate the CO2.

   Regardless of any attempt to wipe out the underground nitrate
   respirers, all our efforts to return carbon to the biosphere will
   encourage Chironian life to proliferate. Conversely, the huge
   quantities of nitrate in the soil will be heaven to human farmers.

   But the water will have to be treated in order to remove the nitrates
   so that it is safe to drink; otherwise the colonists may suffer from
   methaemoglobinaemia, or "blue baby syndrome", where the red blood
   cells are poisoned so they can't take up oxygen. The way to do it is
   to pass ozone through the water to destroy the nitrate.

   Planetologist Del Cotter. UNS Unity, February 24, 2100AD.


Alpha Centauri (c)1998 Electronic Arts. Electronic Arts and the Electronic
Arts logo are trademarks or registered trademarks of Electronic Arts in
the U.S. and/or other countries. All rights reserved. Alpha Centauri and
Firaxis Games are trademarks of Firaxis Games, Inc.

Daniel Boese                            
"I want be accused of and found guilty of morticide. Is that wrong?"