Guermessa is the second moon of Tatooine. In the Tatooine sky, it appears about a quarter the size of Ghomrassen, but this is actually an optical illusion caused by the fact that Guermessa is farther away from the desert planet than Ghomrassen.

Much like its slightly larger sister moon, Guermessa is a gray, cratered, rocky moon without a liquid iron core. This means that it does not possess its own magnetic field and thus is fully exposed to the solar winds of both Tatoo I and Tatoo II. As would be expected in such a case as this, the moon's surface shows a high concentration of Helium-3 atoms (He-3). There is evidence that in the past, before the rise of the Empire, and even before the time of the Old Republic, there was intensive mining conducted on Guermessa to harvest He-3.

Radiometric dating suggests that it was carried out during the era of the Rakatan Infinite Empire and Republic scholars believed that this was perhaps the cause of the rebellion of the Kumumgah against the Rakatan which led to the devastation Tatooine's ecosystem. The Kumumgah, though technologically advanced, preferred to live in harmony with nature and saw the potential destruction of their moons as a horrid prospect, not only to the moons but to Tatooine itself. They defied their masters and sought to remove the mining installation on Guermessa, but in the end, the Rakatan responded to the Kumumgah's disobedience with the ruin of their homeworld.