Arrakis is a desert planet with no natural precipitation, and is the only known source of the spice melange, which extends life and makes interstellar travel possible (and is therefore the most essential and valuable commodity in the universe). The planet has no surface water bodies, and giant sandworms (Shai-Hulud) and their immature forms of sandtrout and sandplankton are among the few fauna on the planet. Open canals called qanats are used "for carrying irrigation water under controlled conditions" through the desert. As indicated by large salt flats, Arrakis once had lakes and oceans.
