FAQ for
Serenity (2005)

Even though the film had 'disappointing' Box Office Records; the DVD sales of the show and film have been overwhelming. So another film, whether it's a sequel or prequel, is now in talks. http://www.worstpreviews.com/headline.php?id=6068&count=25

SERENITY takes place approximately two months after the last "Firefly" episode, 'Objects In Space.'

The events between the final episode of "Firefly" and the beginning of SERENITY, including Inara and Shepherd Book leaving the ship, are chronicled in a three-part comic book series written by Joss Whedon, called 'Those Left Behind.'

Using material compiled by Josh Awtry, the system seems to be a trinary star system, with two other stars orbiting a central one. The Core and Border Worlds orbit the central sun. The second sun, which orbits the central sun in an 80-year orbit, and it's planets comprise the Rim and the Frontier. The third sun orbits the central sun in a 730-year orbit and has no planets listed (although it may at some point be revealed to have its own planetary system). Malcolm Reynolds states (in "Our Mrs. Reynolds") that there are over seventy "little earths" spinning about, all told.

As stated in the commentary and by the clue of the blue sky, the battle is near a planet and inside an ion cloud which has an atmosphere, and therefore sound.