I found this somewhere, but it might be outdated information:
"LV-426 (Acheron) is a satellite orbiting the ringed planet Calpamos in the binary star system Zeta Reticuli, 37 light-years from Sol. It is notable for being home to a colony of Xenomorphs, one of the most dangerous parasitic lifeforms in our galaxy. However, they must rely on the chance visit of other alien species like humans or Space Jockeys. (now known as Ossians) No native species are found here.
The Xenomorph eggs are located in a large room in or beneath a crashed Ossian derelict space vessel. Characteristics of LV-426 (Acheron) Although this satellite is only 2,213 miles in diameter, the gravity of LV-426 (Acheron) is about .86 of Earth's, this hints at a very dense metal core, also from the way people are able to walk on its surface after terraforming for extended periods of time, it seems there is a slight magnetic field. There is a temperature difference (though only slight) which is enough to create the almost constant gales here.
Calpamos and its 3 moons, are only just outside Zeta 2's habitable zone. LV-426 formed from a disc of gas and dust that orbited around Calpamos when this whole system was young, a lot of this material clumped together to form the 3 satellites of which LV-426 is the middle one. The inner moon is called Rosto, similar in size and composition to Europa that orbits our Jupiter. The outer moon is called Varda and is an innert lump of rock very much comparitable to Earth's moon. Varda barely has an atmosphere and there is no detectable water.
The ring system surrounding Calpamos may have been formed from the collision of 2 smaller moons several million years ago, or most likely the residue left over from the original disc of dust and gas that never condensed together. The atmosphere of LV 426, is described by Ash as 'almost primordial', and consists mostly of nitrogen, but also methane, carbon dioxide, ammonia and smaller amounts of other trace elements. The temperature is deep cold, well below the line, circa - 111 centigrade."