Beginning in the early 1970s, the term "space music" was applied to some of the output of such artists as Vangelis, Jean-Michel Jarre, Klaus Schulze and Tangerine Dream, due to the transcendent cosmic feelings of space evoked by the sound of the music and enhanced by the use of the emerging new instrument, the synthesizer, and also in part to the "outer space" themes that are apparent in some of their works. These space music explorations diverged from traditional pop-song formats into longer less structured compositions. Following their early influence on the development of space music, Tangerine Dream later produced increasingly rock-influenced works that are not generally described as space music.