ALPHA CENTAURI SYSTEM

        The Alpha Centauri system is a triple star system. The two main stars are Alpha Centauri A and Alpha Centauri B, while the third star is Alpha Centauri C or Proxima Centauri. The two main stars are in close orbit around their common centre of gravity, while Proxima Centauri is a dim red dwarf star that orbits some distance from the two other stars. In fact, it is not absolutely certain that Proxima Centauri is part of the system, although it seems likely since its proper motion is the same as that of the main stars. At a distance of one tenth of a light year from the main stars, Proxima Centauri takes hundreds of thousands of years to complete one orbit. It has no bearing in terms of gravity or other influences in the solar systems of the two main stars. In fact, Proxima Centauri is not even visible with the naked eye from the surface of Kent.
        The larger star is Alpha Centauri A, a G2-class star that is the near double of Earth's sun in terms of size, luminosity, energy output and most important, stability. It is slightly larger in terms of radius (1.2 times the sun's radius) and mass (1.09 times the sun's mass), so its brightness is somewhat larger, 1.54 times that of the sun. The second star, Alpha Centauri B, is a class K1 star, an orange dwarf, that is somewhat dimmer and cooler than the first star. It's mass is 0.90 that of Earth's sun and its diameter is 0.80 that of the sun. As a result, it is somewhat dimmer and cooler, with only 0.44 times the brightness of the sun. It is also stable. The two stars orbit around a common centre of gravity, the barycentre, and complete one orbit in a span of eighty years. The orbits of the two stars around the barycentre is elliptical. On average, the two stars are separated by 2.9 billion kilometres, roughly the distance that Uranus is from the sun. However, because of the elliptical nature of their orbits, the stars can come as close as 1.7 billion kilometres and be separated by a distance as great as 5.3 billion kilometres. Because the two stars formed from the same cloud of gas and dust that began to contract and spin six billion or more years ago, the planetary systems of both stars are within the same plane as the orbits of the two stars. With two stars that close to each other, planets can only form and have stable orbits only if they fall within one quarter of the minimum distance between the stars. In the Alpha Centauri system, all the planets are within 425 million kilometres of the stars. Planets that would have formed outside of that range would have had unstable orbits and over time, would have either been ejected from the system altogether or had their orbits adjusted to the point that they fall within the limit. This distance is sufficient to allow class-M planets to form and have stable orbits.
        Alpha Centauri A has four planets, and they are given in the table below. All the planets are Earth-sized or smaller. A Alpha Centauri II is the largest planet, while the other three are more Mars-sized or Mercury-sized worlds. The system contains no gas-giant stars, and the number of satellites is very limited, with only Ishtak having one small satellite.

	Name	Distance (km)	Diameter (km)	Rotation	Revolution	Satellites	Classification
I	Utsnob	88,600,000	9984	12.2 days	153.2 days	0	Class J
II	Kent	144,325,000	12619	24.72 hours	337.6 days	0	Class M
III	Vurghu	221,526,000	5938	22.67 hours	1.67 years	0	Class R
IV	Ishtak	377,624,000	4492	2.25 days	2.89 years	1	Class U

The second star, Alpha Centauri B, has just three planets, all Earth-sized worlds or smaller, and they orbit relatively close to the planet. The details are given in the chart below

	Name	Distance (km)	Diameter (km)	Rotation	Revolution	Satellites	Classification
I	Donggon	43,465,000	6232	146.4 days	97.6 days	0	Class V
II	Kensis Babis	79,325,000	11932	31.2 hours	284.2 days	1	Class O
III	Tsapsats	111,530,000	10212	121.5 days	402.2 days	1	Class K

The planets are poor in mineral resources, especially rare earth elements and other elements with higher atomic numbers, reflecting the greater age of the two stars. Both stars have asteroid and comet belts beyond the outermost planet, and the perturbations of these asteroids and comets by the other star in the system causes those small bodies to travel inwards to the planets. As a consequence, Kent experiences a "serious impact event" on average once every ten million years. Extensive evidence suggests that evolution of life on Kent was a start-and-stop proposition, with a large number of extinction events causing significant alteration in the course of evolution. The asteroids are comparatively richer in heavier elements than the planets themselves, and have become important sources of these materials for the Federation. Alpha Centauri C orbits the other two stars from a distance of 13,000 AU (or 1.95 trillion kilometres), and it is a young and dim red dwarf. It does have some planets, but the whole system is too far away from the primary stars to be much of a factor. The two central stars have an overall Oort cloud about 5000 to 6000 AU from the two stars.

Alpha Centauri star system
The double-star Alpha Centauri system showing the distances to scale
A number of small asteroids have been captured by the two stars, and have orbits that are circular and very close to the star. In the case of Alpha Centauri A, one such asteroid orbits at a distance of eleven million kilometres. In the beginning, mankind assumed that these small asteroids were planets and numbered them and the three main worlds accordingly. Thus, Kent was actually A Alpha Centauri VIII in this system. However, since the Kentyans themselves do not count those small bodies as planets (the largest being only twenty-seven kilometres in diameter), the Earth-derived nomenclature was eventually dropped and now, everybody agrees that Alpha Centauri A has only four "real" planets.