Preliminary Report on the Alpha Centauri System The "star" Alpha Centauri, as it appears in Earth’s sky, is actually a grouping of three stars: Alpha Centauri A, ("Alpha Prime") a G2V class main sequence yellow star slightly larger and older than our Sun; Alpha Centauri B ("Hercules"), a K5V orange star which orbits the primary with an aphelion of 35 astronomical units and a perihelion 11 A.U.; and Proxima Centauri, an M5 red dwarf a full light year distant. It is not so much a trinary system as a binary with a third star (Proxima) at a distance. At perihelion, or nearest approach to Alpha Prime, Hercules’ elliptical orbit brings it to about the distance of Saturn from our Sun. The orbital dynamics of a binary star system drastically limit the number of stable orbits available for planet formation. Thus we did not expect to find, and in fact did not find, planets further away from the primary than about 1.5 astronomical units (Earth is one astronomical unit away from our Sun). Two planets make up Alpha Prime’s inner system: Eurytion, a small Mercurylike world, and Chiron. A large Jovian planet, Prometheus, orbits close in to Hercules. Our target destination, Chiron, or "Planet", is a terrestrial world somewhat larger than our Earth. Under a gravitational force of 12.85 m/s2 (compared to Earth’s 9.81), colonists will feel 1.31 times heavier than on Earth, which will be uncomfortable at first but should not cause drastic longterm health problems. Chiron is somewhat farther from Alpha Prime than Earth is from our Sun (1.07 A.U.), but the higher luminosity of Alpha Prime more than offsets this. Moreover, since Alpha Prime is somewhat larger than the Sun, its size in Chiron’s sky will be indistinguishable from our Sun. Chiron’s higher gravity results in a thick, dense atmosphere, so we can expect to find larger and more numerous flying creatures than on Earth. The massive preponderance of nitrogen in the atmosphere (over 90%, compared with Earth’s 78%) has several significant implications. First, the dangers of nitrogen narcosis with prevent humans and terrestrial animals from breathing the unfiltered air. Secondly, the low oxygen partial pressure will tend to suppress fires. Chiron’s two moons, tiny inner Pholus and the somewhat larger Nessus, are each much smaller than Earth’s moon, but they orbit much closer in, so the overall tidal effect is comparable to Earth’s.
Chironian Calendar Chiron’s year is slightly longer than Earth’s, but it rotates considerable faster, finishing a day in slightly under 18 hours. Since there is no further point in retaining hour, minute, and second time measurements calibrated for Earth time, the following calendar will be used on Planet: The hour, the minute, and the second will each be shortened by approximately 2.68%, in order to accomodate a Chironian day of precisely 18 hours. The 532 days in a year shall be divided into 53 ten day long "decurns", which corresponds both to the approximate length of Earth’s week and the approximate length of Chiron’s lunar month (measuring by the cycles of the larger moon, Nessus). The two "leftover" days shall be used as special holidays. The first day of the year shall be "Planetfall Day", on which we celebrate our arrival on Planet. The middle (27th) decurn of the year shall also be a time of celebration, and shall end on "Earth Day", the second extra day, on which we remember Earth, our lost home planet.
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 m2 5.10E+14 7.18E+14 1.41 Standard gravity m s2 9.81 12.85 1.31 Escape velocity m s1 11184 13947 1.25 Density kg m3 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 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 m3 1.22 2.06 1.68 "Flammability" mmol K J1 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 m2 1383 1750 1.27 Outer Moon (Nessus) The Moon Nessus 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 m2 3.80E+13 8.04E+12 0.21 Mean gravity m s2 1.62 0.68 0.42 Density kg m3 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 Inner Moon (Pholus) The Moon Pholus 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 m2 3.80E+13 1.54E+12 0.04 Mean gravity m s2 1.62 0.28 0.17 Density kg m3 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 m2 5.10E+14 9.98E+13 0.20 Standard gravity m s2 9.81 4.33 0.44 Escape velocity m s1 11184 4942 0.44 Density kg m3 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 m2 1383 8999 6.51 
