From: Daniel Boese <dboese@nev.npiec.on.ca>
Subject: Sid Meier's Alpha Centauri
Date: 1998/08/04
Message-ID: <6q7k7h$31f$1@brain.npiec.on.ca>
X-Deja-AN: 377902017
Organization: Niagara's Electronic Village
Followup-To: rec.arts.sf.science
User-Agent: tin/pre-1.4-980226 (UNIX) (IRIX/5.3 (IP22))
Newsgroups: rec.arts.sf.science,rec.arts.sf.misc
(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 www.alphacentauri.com. 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
planet.
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
humans.
The much higher nitrogen partial pressure (and resulting lower oxygen
partial pressure) will tend to make things like forest fires
considerably less likely.
-----
PLANETS OF ALPHA CENTAURI A
===========================
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
Chiron
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
Atmosphere
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
sunlight.
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.
Oceanography
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
Sea).
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.
Ecology
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
environments.
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
light
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 dboese@nev.npiec.on.ca
"I want be accused of and found guilty of morticide. Is that wrong?"
DataPacRat's Warren
Why should I believe that?
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