Pythos is a multiple-star system consisting of a red dwarf and white dwarf in close orbit, with an orange subgiant as a distant companion. (Most modern astronomers believe that 50% or more of all star systems are multiples.)
The dwarf pair orbit around their center of mass, circling that point with a separation of 1.5 SU (about the distance from our Sun to Mars) in a period of 300 days. The red dwarf is an extremely faint star with a solar mass of 0.2 and a solar diameter of 0.6 (therefore it is only 20% as massive as Earth's sun, and only 60% as large). The white dwarf is a dim star with a solar mass of 4.8 (almost five times as heavy as our Sun) squeezed into a volume of only 0.02 solar radii (so it's only a bit more than twice the size of the Earth).
The subgiant and the dwarf pair follow overlapping elliptical orbits around their center of mass, completing one loop every 1,470 years. The subgiant is a brilliant star, roughly 13 times more luminous than our Sun. The maximum separation between the subgiant and the dwarf pair (called apastron) is 540 SU, while their closest approach (periastron) is just 60 SU. For comparison, Neptune orbits our Sun at a distance of about 30 SU. The Libra fleet will be visiting Pythos at a point somewhere near periastron.
A single gas giant orbits (circumprimary) the orange subgiant at a distance of approximately 50 SU. At this distance, the orange star appears to be twice as bright as the Sun, but only about one-twelfth its size. The gas giant planet has a mass of approximately 25 times that of the Earth, and a diameter of roughly 5 times that of the Earth. It's rotation period is 23.5 hours, and it revolves once around the orange subgiant every 458 years. It is a blue, Neptune-like world, made up of 85% hydrogen.
Pythos is a terrestrial (Earth-sized) moon of the gas giant, orbiting at a mean distance of 425,000 miles (about 10% farther out than our Moon), completes a revolution every 8.4 days. It rotates at a 3:2 ratio, once every 12.6 days. The planet is geothermally active, venting large amounts of hydrogen sulfide gas, which then breaks down due to heat and solar radiation, producing oxygen, liquid water, and monatomic sulfur. The volcanic regions of the planet are covered with sulfur (brimstone) plains.
Viewed from Pythos' surface, the gas giant rises and sets just as the orange sun does. From planet-rise to planet-rise will take twice the rotational period, or 25.2 days. Only half of the planet's surface ever experiences an eclipse, but when it does, the eclipse occurs every two rotations at the exact same time. As an example, for a point at which the planet and the sun rose at the same time, the planet would be one-fourth of the way up when the sun reached its zenith, and the planet would be overhead at sunset. The next sunrise would be concurrent with 'planet-set', and the planet would not be visible for the following 'day'. After that, once again the planet would rise as it eclipsed the sun, and the process would repeat. (Keep in mind that a 'day' on Pythos equals 12.6 Colonial Standard days.)
The gas giant has a second moon which trails along in an orbit 'behind' Pythos due to the effects of the larger moon's gravity. This moon has been code-named "Duckling".
The Shell Nebula
This trinary star system is a cataclysmic variable system, with the white dwarf undergoing a 'dwarf nova' event every 11 to 17 days, and experiencing a 'superoutburst' approximately twice per orbital cycle, every 150 days. The nova phenomenom are caused by the ejection of matter from the red dwarf, which creates an accretion disk around the white dwarf, and thermonuclear detonations on the surface of the dense star as matter reaches its surface. The white dwarf is essentially consuming its close companion, with disastrous results.
The origin of the superoutbursts is still in question, but they reach a luminosity of nearly 200 (about twice as bright as our Sun), and have created a multilayered shell nebula around the system. This nebula extends outward approximately 2.4 LY from the systems' center of mass. These shells are not precisely concentric, having been cast off at slightly irregular intervals. The presence of the orange subgiant creates a hole effect in the shell, as the matter ejected toward the companion star is captured by the subgiant's gravity